Louisiana State University LSU Digital Commons
LSU Historical Dissertations and Theses Graduate School
1980 Genetic Study of Heat Tolerance; Size of Stigma, Style and Ovary in the Tomato, Lycopersicon Esculentum. Hanna Yacoub Hanna Louisiana State University and Agricultural & Mechanical College
Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses
Recommended Citation Hanna, Hanna Yacoub, "Genetic Study of Heat Tolerance; Size of Stigma, Style and Ovary in the Tomato, Lycopersicon Esculentum." (1980). LSU Historical Dissertations and Theses. 3484. https://digitalcommons.lsu.edu/gradschool_disstheses/3484
This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact [email protected]. INFORMATION TO USERS
This was produced from a copy of a document sent to us for microfilming. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the material submitted.
The following explanation of techniques is provided to help you understand markings or notations which may appear on this reproduction.
1.The sign or “ target” for pages apparently lacking from the document photographed is “Missing Page(s)”. If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting through an image and duplicating adjacent pages to assure you of complete continuity.
2. When an image on the film is obliterated with a round black mark it is an indication that the film inspector noticed either blurred copy because of movement during exposure, or duplicate copy. Unless we meant to delete copyrighted materials that should not have been filmed, you will find a good image of the page in the adjacent frame.
3. When a map, drawing or chart, etc., is part of the material being photo graphed the photographer has followed a definite method in “sectioning” the material. It is customary to begin filming at the upper left hand corner of a large sheet and to continue from left to right in equal sections with small overlaps. If necessary, sectioning is continued again—beginning below the first row and continuing on until complete.
4. For any illustrations that cannot be reproduced satisfactorily by xerography, photographic prints can be purchased at additional cost and tipped into your xerographic copy. Requests can be made to our Dissertations Customer Services Department.
5. Some pages in any document may have indistinct print. In all cases we have filmed the best available copy.
University Microfilms International 300 N. ZEEB ROAD, ANN ARBOR, Ml 48106 18 BEDFORD ROW, LONDON WC1R 4EJ, ENGLAND 80217^6
HANNA, HANNA YACOUB
GENETIC STUDY OF HEAT TOLERANCE; SIZE OF STIGMA, STYLE AND OVARY IN THE TOMATO, LYCOFERSICON ESCULENTUM
The Louisiana State University and Agricultural and Mechanical Col.
. . . ., PH.D. 1980 University Microfilms International 300 N. Zeeb Road, Ann Arbor, MI 48106 18 Bedford Row, London WC1R 4EJ, England PLEASE NOTE:
In all cases this material has been filmed in the best possible way from the available copy. Problems encountered with this document have been identified here with a check mark .
1. Glossy photographs ^
2. Colored illu stratio n s ______
3. Photographs with dark background ^
4. Illustrations are poor copy ______
5. °rint shows through as thereis text on both sides of page ______
6. Indistinct, broken or small print on several pages ______throughout
7. Tightly bound copy with print lost in spine ______
8. Computer printout pages with indistinct print ______
9. Page(s) ______lacking when material received, and not available from school or author ______
10. Page(s) ______seem to be missing in numbering only as text follows ______
11. Poor carbon copy ______
12. Not original copy, several pages with blurred type ______
13. Appendix pages are poor copy ______
14. Original copy with light type ______
15. Curling and wrinkled pages ______
16. Other
Universiiv M iard T iim s International
200 \ Z=== PQ. ANN AH3QP Ml JS-0 6 ‘313! 761-4700 GENETIC STUDY OF HEAT TOLERANCE; SIZE OF STIGMA, STYLE AND OVARY IN THE TOMATO, LYCOPERSICON ESCULENTUM
A Dissertation
Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfilment of the requirements For the degree of Doctor of Philosophy
in
The Department of Horticulture
by Hanna Yacoub Hanna B.S., The High Agricultural Institute, El Minya, Egypt, 1963 M.S., Assiut University, Egypt, 1972 May 1900 ACKNOWLEDGMENTS
I wish to express my appreciation to Dr. Teme P. Hernandez for directing this research study. His guidance, encouragement, and sincere interest have been most helpful. I am also very grate ful to Dr. Donald W. Newsom, Head of The Department of Horticulture for his assistance v/hich not only enabled me to complete this work, but also to regain sight in one of my eyes by miracle surgery conducted by Dr. Herbert E. Kaufman, one of the finest corneal surgeons in the world and Head of The Department of
Opthalmology at L.S.fJ. Special thanks are extended to Dr.
Merlin T. Henderson, Dr. Kenneth L. Koonce for their valuable help in the statistical analysis of the data, to Dr. James F.
Fontenot, Dr. Roysell J. Constantin for helping me in many ways. TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS...... ii
TABLE OF CONTENTS...... H i
LIST OF TABLES...... iv
LIST OF FIGURES...... viii
ABSTRACT...... ix
INTRODUCTION...... 1
LITERATURE REVIEW...... 3
MATERIALS AND METHODS...... 19
EXPERIMENTAL RESULTS...... 31
Test 1 - Germplasm Experiment ...... 31
Test 2 - Dial lei Experiment ...... 49
Test 3 - Study of Morphological Abnormalities of Flowers, Fruit Set and Inheritance of Stigma and Style Diameter and Ovary - Shape...... 62
DISCUSSION...... 84
SUMMARY...... 92
LITERATURE CITED...... 96
AUTOBIOGRAPHY...... 101
in* ♦ • LIST OF TABLES
Table Page
1. Weekly minimum, maximum and average temperature (C) during a 13 week period in Summer 1978 and Spring 1979 ...... 39
2. A comparison of mean percentage fruit set of six tomato cultivars in two seasons ...... 40
3. Statistical comparison of each of six tomato cultivars between seasons for mean percentage fruit se t...... 40
4. Mean percentage normal flowers for tomato cultivars in two seasons ...... 41
5. Mean percentage flower drop for each of six tomato cultivars in two seasons ...... 41
6. Statistical comparison of each of six tomato cu lti vars between seasons for mean percentage flower drop...... 42
7. Mean percentage dormant ovaries for each of six tomato cultivars in two seasons ...... 42
8. Statistical comparison of each of six tomato cu lti vars between seasons for percentage dormant ovaries ...... 43
9. Mean fruit weight for each of six tomato cultivars in two seasons ...... 43
10. Statistical comparison of each of six tomato cultivars between seasons for mean fru it weight ...... 44
11. Mean number of seed per fruit for each of six tomato cultivars in two seasons ...... 44
12. Statistical comparison of each of six tomato cultivars between seasons for mean number of seeds per fr u it ...... 45
13. Simple correlation coeffecient between fru it weight and seed number within each of six tomato culti.vars for two seasons ...... 45 iv Table Page 14. Mean weight of 100 seeds for each of six tomato cultivars in two seasons ...... 46
15. Statistical comparison of each of six tomato cultivars between seasons for mean weight of 100 seeds ...... 46
16. Percentage of seed germination for each of six tomato cultivars intwo seasons ...... 47
17. Statistical comparison of each of six tomato c u lti vars between seasons for percentage of seed germi nation ...... 47
18. Percentage of normal pollen grains for each of six tomato cultivars intwo seasons ...... 48
19. Statistical comparison of each of six tomato c u lti vars between seasons for percentage of normal pollen ...... 48
20. Mean percentage of fruit set of F^ tomato hybrids in a dial lei test of seven parents ...... 53
21. Analysis of variance of 21 F, hybrids for percen tage of fruit set 54
22. General and specific combining ab ility of seven tomato parents in a dial!el test for percentage of fruit s e t...... 55
23. Mean percentage of flower drop of F, tomato hybrids in a dial lei test of seven parents...... 56
24. Analysis of variance of 21 F. hybrids for per centage flower drop 7 57
25. General and specific combining ab ility of seven tomato parents in a diallei test for percentage flower drop ...... 58
26. Mean percentage dormant ovaries of F, tomato hybrids in a dial lei test of seven parents ...... 59
27. Analysis of variance of 21 F. hybrids for dormant ovaries ...... 7...... 60
v Table Page 28. General and specific combining ability for seven tomato parents in a dial lei test for percentage of dormant ovaries ...... 61
29. Mean percentage of normal flowers, standard error and coefficient of variability of parents, F., F9 and backcross generations of L401 X Chico III in Summer of 1978 ...... 72
30. Mean percentage of normal flowers produced by L401 and Chico IIItomato cultivars in Spring (1979) ...... 73 r 31. Mean percentage fruit set of parents and progenies of the cross L401 X Chico III in the Summer of 1978 ...... i ...... 74
32. Frequency distribution of plants, mean, variance and coefficient of variability for stigma diameter in parents and progenies in the cross: L401 X Chico I I I ...... 75
33. Comparative stigma diameter (mm) for observed and theoretical means, mean difference, potency, skewness and minimum number of genes in the cross: L401 X Chico I I I ...... 76
34. Genetic and total variance of stigma diameter and heritability in the generation of the cross: L401 X Chico III...... 7...... 77
35. Frequency distribution of plants, mean, variance and coefficient of variability for style diameter in parents and progenies in the cross: L401 X Chico I I I ...... 78
36. Comparative style diameter (mm) for observed and theo retical means, mean difference, potency, skewness and minimum number of genes in the cross: L401 X . Chico I I I ...... 79
37. Genetic and total variance of style diameter and heritability in the F„ generation of the cross: L401 X Chico I I I 7...... 80
38. Frequency distribution of plants, mean, variance and coefficient of variability for ovary shape index in parents and progenies in the cross: L401 X Chico I I I ...... 81 vi Table Page
39. Comparative ovary shape index data'for observed and theoretical means, mean difference, potency, skewness and minimum number of genes in the cross: L401 X Chico I I I ...... 82
40. Genetic and total variance of ovary shape and heri tability in the F„ qeneration of the cross: L401 X Chico I I I ...... f ...... 83 LIST OF FIGURES
Figure Page
1. Daily maximum, minimum and mean temperature for July 1-28, 1978 ...... 32
2. Normal flowers produced by 'Chico III' (left) and ' L401' (right) in the summer season ...... 63
3. Abnormal flowers produced by ' L401' in the summer season ...... ■...... 64
4. ' L4011 (left) and 'Chico III' (right) tomato flowers showing the stigma, style and ovary after removing the calyx and corolla...... 67
v m* *■ m ABSTRACT
Genetic studies were conducted on heat tolerance, size of
stigma, style and ovary in the tomato, Lycopersicon esculentum
Mill, in a series of experiments.
Several cultivars were compared under summer and spring grow
ing conditions for fruit set, flower drop, dormant or undeveloped
ovaries, fruit weight, seed number per fru it, mean weight of 100
.seeds, percentage of seed germination and non-aborted or normal
pollen grains. In the Summer of 1978 the average minimum temperature
was 24°C and maximum was 34.6°C. In Spring 1979 the average
minimum temperature was 15.6°C and the maximum was 25.3°C.
'BL6807* set the highest percentage of fruits (50.5%) in the summer;
whereas, 1L401* had the lowest fru it set of 1.1%. 1BL6807'
had the smallest number of flowers to drop or absciss in the
summer and 1CL9-0-0-1 ’ had the lowest percentage of dormant
or undeveloped ovaries. 1B16807' had the statistically highest
percentage of stained pollen grains in the summer indicating
good viable pollen. In general the cultivars had less pollen
in the summer than in the spring; however, differences occurred
among cultivars in the summer. The mean fru it weight of the
cultivars during the summer was generally lower than in the spring
with the exception of ' BL6807', 'Saladette', and 1S69161 which were the same. The same was true for mean seed weight and seed
number except 'CL9-0-0-r and 'Chico III1 which had no significant difference in seed number between seasons. There was a highly significant positive correlation between fru it weight and seed number for the cultivars in both seasons. The percentage germination of the seeds produced in the summer season was lower than those produced in the spring with the exception of 'Saladette' which showed no difference. ' L401' had very low fruit set in the summer having many flowers with sp lit antheridial cones and elongated styles. This test showed that 1BL6807' was the most heat tolerant cultivar and 1L401’ was the most heat sensitive. 'Saladette1,
' S6916' and ’CL9-0-0-11 cultivars also showed heat tolerance by the fairly high percentage of fruit set. 'Chico III' did not show an appreciable amount of heat tolerance because i t had only
11% fruit set which was significantly lower than other cultivars except ' L4011.
In a dial lei test 'S6916' transmitted good fruit setting ability to its progenies having less flower drop and fewer dormant ovaries.
'BL6807' was the next best parent for transmitting fruit setting ability and less flower drop, however, it transmitted the character for dormant ovaries to its progenies. *L401 - had the lowest general combining ability value for fruit set indicating that this tomato cultivar consistently transmitted less fruit setting ability to its progenies at high temperature. Additive gene effect for fruit set, flower drop and dormant ovaries, was more important than non-additive effects. The ability to produce normal flowers and to set a relatively
high percentage of fruits in the cross 1L401* X 'Chico III*
appeared to be under a heritable mechanism with some dominance.
This cross also showed that stigma diameter, style diameter and
ovary shape are under a heritable mechanism showing a partial
dominance of the small stigma diameter, style diameter and some
dominance of the 'Chico III' ovary shape. Heritabilities were
40.2-49.4% for stigma diameter, 72.8-74.4% for style diameter and
72.8-80.7% for ovary shape. INTRODUCTION
The tomato,' Lycopersicon esculentum, Mill, is one of the
most popular vegetable crops in this country. In 1977 Rick
(42) reported that there were 198,818 hectares, valued at 914.1
million dollars, grown commercially in the United States. The
average per capita consumption in 1977 was 25.5 kg. To continue
meeting the increasing demand for this crop it will be necessary
to expand the production into areas where present day cultivars
cannot be grown economically because of biological stress effects,
especially from high night and day temperatures. Tomato pro
duction in the United States can be divided into seven seasonal
periods, grouping some of the major states in each season as
follows: {1J winter - Florida; (2) early spring - Florida,
Texas and California; (3) late spring - Louisiana, South Carolina,
Georgia and California; (4) early summer - 13 states including
California, New Jersey, Alabama, Tennessee, Arkansas, and Maryland;
(5) late summer - Michigan, New York, Ohio, Pennsylvania and
11 other states; (6) early fall - California; (7) late fall -
Florida and Texas. The characteristic of the inability of present
tomato cultivars to set fruit under adverse weather conditions
such as high night and day temperatures has been the greatest
limiting factor in extending the seasonal harvests especially
in the south and other sub-tropical and tropical areas of the world. New cultivars having the ability to set and mature
1 2
fruit of good horticultural quality under these stress periods would enable the tomato industry for the fresh and processing markets to develop,enabling shifts in production into new areas of the United
States and the world.
This study was conducted to evaluate factors affecting fruit set under adverse environmental conditions, to study the general and specific combining ability of heat tolerant cultivars and to evaluate the inheritance of this character and others. LITERATURE REVIEW
The tomato, Lycopersicon esculentum, Mill., is one of the most important vegetable crops in the United States and in the world. To continue meeting the increasing demand for this crop it will be necessary to expand the production into areas where present day cultivars cannot be grown economically because of biological stress effects, .especially from high night and day temperatures.
Smith (48) found in 1932 that blossom drop in tomato was greatly increased by hot dry winds and low humidity as well as by low moisture. Few flowers that had elongated stylesin hot dry weather developed normally and set fruit.
Nightingale (37) reported in 1933 that respiration in tomato plants exceeded carbon dioxide assimilation at 35°C.
The concentration of carbohydrates was decreased followed by breaking down of complex proteins to simpler forms of organic nitrogen which accelerated growth for a few days, but death of the plants finally resulted.
In further studies Smith (49) indicated that extremely high temperature caused the styles to elongate abnormally and exceptionally early. This condition resulted in destruction of the stigmatic surface before pollination was effected. These flowers therefore failed to become fertilized and soon abscissed.
Smith and Cochran (50) studied the germination of tomato pollen
3 4 grains as well as the rate of pollen tube growth and found that germination was best at 29.4°C. The maximum rate of pollen- tube growth occurred at 21.1°C.
The rate of stem elongation and the setting of fruit of tomato plants was studied by Went (57) in 1944. He .found that the optimum temperature for vegetative growth and fruit develop ment was 26.5°C during the day and 20°C during the night. One year later Went (58) showed that at night temperature above
18°C, translocation of sugar limited the growth of a tomato plant as a whole including stem, root, and fruit growth.
Mullison and Mullison (36) reported that under conditions of high night temperatures many tomato flowers normally failed to set fruit. When flowers were sprayed with certain growth regulators, higher total yield and larger fruit size were obtained than the controls. Of the tomato cultivars studied, whether or not the plants were treated, the determinate type was superior to the indeterminate for fruit production during the tropical hot season. The relation between sugar translocation in tomato plants and temperature was also studied by Went and Hull
(59). According to their study the amount of sugar translocated gradually increased as the temperature was lowered.
Leopold and Frances (30) working with excised tomato flowers demonstrated that the capacity for fruit set is dependent upon the temperature and this dependency is inherent in the ovary 5 itself. The optimum temperature range was found to be 18-22°C.
It was demonstrated that abscissed flowers are capable of setting fruits and that non abscissed,undeveloped ovaries are like-wise capable of setting fruit and developing when supplied with nutritive material.
Moore and Thomas (35) reported that high temperature alone was not the only factor associated with the poor fruit set on the first two clusters. Their results strongly suggest that the combined effect of high light intensity and high temperature or solar radiation were associated with poor fruit set. The failure to set fruit in tomato was hot due to a lack of pollen or to any mechanical factor that might prevent pollen from reaching the stigmatic surface. Under these test conditions a growth substance applied to the flower clusters and/or reducing the the light intensity by 50% appeared to be a practical aid to growers in obtaining late summer or early fall tomatoes.
Bohning, Kendall and Li nek (4) found that the optimum temperature for carbohydrate translocation occurred at approxi mately 24°C.
Johnson and Hall (26) indicated that low carbohydrates were not the main reason for the failure of fruit set in
'Pearson' tomato plants. Sucrose or urea sprays did not induce fruit set in the 'Marglobe' plants. Their results suggested that either the pollen was not viable or that fertilization was not successfully completed. 6
According to Osborne and Went (38) high day and night
temperatures of 30°C caused infertile flowers to be differen
tiated, irrespective of photoperiod of 8 or 16 hours and under
these conditions a spray of 2-naphthoxya.cetic acid (2NA) was
ineffective for inducing fruit set. Under lower temperature
percentage fruit set was generally'somewhat higher in 2NA
treated blossoms, while at very low temperature there was an t indication that 2NA may have induced a higher fruit set than would occur naturally. Under all conditions studied 2NA pre
vented the abscission of sprayed blossoms even when fru it form
ation did not occur.
In 1954 Johnson and Hall (27) reported that two responses correlated with high temperatures were found to be associated with parthenocarpy. The firs t was a tendency for many cultivars to exhibit style exsertion, hence pollen failed to be effective.
The second response was the loss of pollen viability at temperatures above 32.2°C. If either condition was present fertilization was either reduced or did not occur and any fruits that developed were partially or entirely seedless. A high degree of seed lessness was observed in conjunction with high temperature condition.
Johnson and Hall (28) reported that 'Marglobe' and 'Rutgers' plants grown at high temperature and high light intensity grew slowly but did not fruit. 'Marglobe' and 'Rutgers' plants in the field did not respond to sprays of parachlorophenoxyacetic 7
acid (CPA) during unfavorable light-temperature. period; whereas
in summer, cultivars and selections sprayed with CPA nearly
doubled their fruit production. Dormancy of fruits of the
S-616 cultivar could have been attributed primarily to high light
conditions.
A good correlation was found by Verkerk (54) between size
of the fruit and the number of seeds per fruit, but the greater
the number of seeds the lower was the mean weight per seed.
They further reported that when poor conditions for tomato
growing exist, the emphasis should be on good tomato pollination.
Liverman and Johnson (33) found that fruit growth and develop ment were arrested or dormant in the 'Marglobe' cultivar grown in
the field under the high light and temperature of summer.
The condition of "summer dormancy" in tomatoes amounts to a
very marked reduction of growth of both vegetative and repro
ductive structure.
Howlett (19) emphasized that both night and day air tempera
tures are important factors affecting fruit set. He showed
that day temperatures ranging from 25°C to 29.4°C decidedly
reduced fruit numbers in Ohio WR-7 tomato cultivar. Night air
temperatures were particularly important in influencing the
number of flowers reaching anthesis, the fertility of male
gametes, ease of distribution of the pollen, and the various
processes associated with fertilization and development of the
embryo and endosperm. 8
Schaible (46) showed that substantial levels of heat tolerance were identified in two cultivars, 'Narcarlang' and 'Porter' which set fru it abundantly at night temperatures of 22.8°C and 26.7°C.
'Rutgers', 'Improved Garden State', 'Ace', and 'Sioux' set very few fruits at the same night temperatures. . Fruit size in.general decreased as night temperatures were increased. Fruit seediness of each cultivar was related to the degree of heat tolerance.
Calvert (6) in a review of literature on the subject "pollen viability, germination and growth in the tomato" reported that under conditions of mild carbohydrate deficiency pollen grains developed which were morphologically perfect and stained satis factorily failed to germinate either on the stigma of flowers or on agar media.
Iwahori and Takahashi (25) reported'that flower buds nine to five days before anthesis and flowers one to three days after anthesis were highly susceptible to high temperature (40°C). High temperature treatment adversely affected both pistil and stamen in the flower buds nine days before anthesis while it affected mainly the stamen in the bud stage five days before anthesis. CPA spray improved setting o.f flowers treated under high temperature after anthesis, but did not increase the setting of flowers treated in the bud stages.
A highly positive correlation was found between the number of seeds per fru it and fru it weight.
Davis, Smith, Schweers and Scheuerman (11) found that there can be important fru it set in the absence of successful pollination and 9 the number of seeds produced is a quantitative index of floral fe rtility .
According to Dempsey and Boynton (12) number of seeds per fru it was significantly correlated with fru it weight in the c u lti vars, 'Pearson* and 'San Marzano*. Each additional seed increased fruit weight by about one gram. They also indicated that fruits can be set with a few grains of pollen and develop with only a few seeds.
Hussey (20) found that temperature did not affect the amount of respiratory loss in young tomato seedlings durinq the night at a temperature range of 15-25°C.
Iwahori (22) found that both macro-micro spore mother cells in meiosis stages (nine to eight days before anthesis) were easily affected by a high temperature treatment. The injuries from high temperature decreased in the advanced stages of flower bud develop ment. In one to three days before anthesis no morphological dis turbance by the treatment was observed in the pollen or ovules.
Iwahori (23) indicated that almost all ovules which were treated with high temperature 18 hours after pollination aborted and in his opinion this strongly suggested that the elongation of pollen tubes was affected and fertilization did not take place.
The endosperm was more susceptible to high temperature than the proembryo and the cell contents of the endosperm easily became empty or deeply stained and degenerated. However, the endosperm 10
and proembryo treated at the same advanced stages showed resistance
to high temperature. When ovules were treated five days after
pollination, there were hardly any abnormalities.
Iwahori (24) studied the effect of high temperature on auxin
level in the tomato. He found that the treatment with high temp
erature resulted in the disappearance of the first rise of auxin
level. According to him these data suggest that the first rise
of auxin level may be the trigger for fru it development. He
showed that almost all auxin activity was detected only in the
seeds. Accordingly, in the treated ovary of tomato flower, ferti
lization will not take place, and this would result in the failure
of auxin production which is assumed to act as a trigger for
fru it development.
Saito and Ito (45) found that the higher night temperature and/or
the lower light intensity retarded the morphological development
of flowers. These flowers were smaller having smaller sepals,
petals, ovaries and especially smaller anthers and heavy flower
drop.
Abdalla and Verkerk (1) reported that stem growth of tomatoes was twice as fast at 35°C day and 25°C night compared with normal
temperature of 22°C. The plants produced thin stems and many
trusses with weak flowers. In many cases styles were as long as or
even longer than the stamen tube. Flower shedding was markedly
increased and only half the number of fruits developed at the first IX
two trusses. Pollen germination in vitro is best at 27°C, but
tube growth of pollen from high temperature was slower than
from normal temperature. Pollen from dehisced flowers gave practi
cally no germination and tube growth. Counts of pollen on the stigma
showed only very limited amounts present at high temperatures, but
at normal temperatures pollen was plentiful.
Coyne (10) was interested in the effect of high and low soil moisture on style elongation in tomato flowers. According to his data 'Narcarlang' and 'Polar Circle' cultivars showed a significant
increase in length under soil moisture stress. Under high soil moisture the stigmas of 'Narcarlang' were almost level with the
tip of the anther cone, but protruded over 2 mm under the low
soil moisture treatment.
Rick and Dempsey (43) showed that stigma level did not com pletely account for the high fruitfulness of numerous Fg segregates
that had stigmas at levels as low as the lower parent.
Lipton (32) grew tomatoes in Tucson, Arizona in a closed
humid greenhouse and compared them with those grown in a normal vented one. The plants in the humid greenhouse lacked vigor in the spring, were prone to high temperature injury in the summer, and had poor fru it set in both seasons. Elongation of plants in the humid house during early growth exceeded those in the normal house only when relative humidity was near 100%. High humidity reduced fru it quality in the summer but not in the spring, inducing 12 uneven fruit coloration, cracking and surface dullness. These defects reduced yields of marketable fru it by approximately 56%.
Charles and Harris (8) reported that at 26.7°C the high level of the stigma in the antheridial cone of the tomato flower was the main factor in reducing fruit set, but low stigma receptivity was also a factor in some selections.
Imanishi and Hiura (21) found that there was a positive cor- i relation between fruit weight and seed content within a cultivar and hence environmental conditions positively affected the two characters. Furthermore, i t was also inferred that there were cultivar differences, namely, genotypic defferences among the degrees of the association expressed by correlation and the directions of the association expressed by regression. Their data suggested that the direct improvement of fruit weight by tomato breeding has been accompanied with the indirect increase of seed content.
Stoner and Otto (53) proposed a screening method to select for high temperature fruit setting ability in the tomato on the basis of fru it set under high summer temperatures in the greenhouse.
Under their screening method 'Chico III' set the highest percentage of fruits.
Rudich, Zamski, and Regev (44) indicated that high temperature conditions (39 ± 2°C day and 22 ± 2°C night) caused deficient fruit set in tomatoes. Fruit set of 12 cultivars from divergent sources ranged from 0% to 22% while that of 'Saladette' was 13 between 56% and 60%. The impaired fru it set of 'Roma VF' was found to be associated with low pollen viability, style elongation, and lack of formation of the endothecium, which is essential to stamen and anther opening. In 'Saladette' damage was slight or non existent, and the endothecium formed normally under high temperature conditions. The pronounced differences in cultivar response to high temperature permit the breeding of tolerant cultivars and the study of the nature of the primary physiological processes that impede fruit set.
Levy, Rabinowitch and Kedar (31) studied fru it setting ability among seven tomato cultivars under high temperature conditions.
They found that fruit set varied from 77.3% in the heat tolerant cv. Hot set, 62% in cv. Gamad to 16.3% in the most sensitive cv. Hosen-Eilon. The characters contributing to low fru it set were bud drop, splitting of the antheridial cone, style exsertion and reduction of the quantity and/or functionality of the gametes.
Using the above characters as criteria for selecting, fruit set of an F^ line, phenotypically similar to the sensitive parent, was improved to 63.1%. Improved fru it set of 87.6% was also obtained in an Fj hybrid between 'Hotset' and 'Gamad'.
Shelby, Greenleaf and Peterson (47) concluded that open pollination at high temperature was insufficient for maximum fruit set in both heat tolerant and heat sensitive cultivars and, further, that the pollination effectiveness of the la tte r was more impaired at high 14 temperature than that of heat tolerant tomatoes.
Stevens and Rudich (51) reported that in both the U.S. and
Israel, 'Saladette' tomato cultivar has been used as a source of genes for high temperature fruit set in breeding programs and the results have been very promising. They added that the screening of segregating populations in greenhouses during summer months permits vigorous evaluation for high temperature fru it set.
Using this procedure i t has been possible to develop improved lines which set fruit from virtually every flower when other culti vars are dropping all of their flowers.
Stoner (52) in his article titled "Breeding Vegetables Tolerant to Environmental Stress" supports the approach of Leeper at Texas
A&M University to breed tomatoes for high temperature tolerance.
In his opinion, the most successful way is to rely on planting in an area and at a time of the year when high temperatures are common and then continually selecting those lines or parents that produce fruits. He mentioned that the great progress in breeding for heat tolerance has been made when segregating germplasm was grown and evaluated in an area where stress occurred naturally.
Villareal et a l. (56) reported on their method of screening for heat tolerance in the genus Lycopersicon and found that less than
1% or 38 out of 4,050 accessions of a world collection of the garden tomato (Lycopersicon esculentum Mill.) and related Lycopersicon species displayed a high level of heat tolerance based on fruit 15
setting ability at high temperature. Thirty of these heat-tolerant
accessions belonged to Lycopersicon esculentum, seven to L_.
pimpinellifolium and one was a cross between L_. esculentum and
U pimpinellifolium.
Kuo et al. (29) in an article titled "Tomato Fruit Set at
High Temperature" indicated that poor fru it set at high temperature,
usually above 30°C, is not due to a single factor but to many
and diverse characters. Each of a number of physiological phenomena
may account for some reduction in fruit set. In their opinion,
the damaging effect of high temperature on several heat-tolerant
cultivars was consistently less on some physiological or morpho
logical characters analyzed than those in heat sensitive cultivars.
Villareal and Lai (55) conducted four experiments to clarify
environmental influence on heat-tolerance expression. Their findings
from these experiments suggested that the heat-tolerant genes may
be easily influenced by environmental conditions. In their opinion, heat-tolerant selections should be tested in as many
locations and seasons as possible before any recommendations are made.
El Ahmadi and Stevens (13) studied the high temperature responses of several heat-tolerant tomatoes, Lycopersicon esculentum H ill., using cvs. Saladette, PI262934, BL6807, S6916, CIAS161, and
VF36, grown at 38°C day and 27°C night temperatures. They
found that flower production was reduced in all cultivars except 16
1BL68071,• 'Saladette', and 'VF36' and these lacked stigma exsertion in the flowers. Pollen production was reduced in all cultivars, and there was a lack of pollen dehiscence. 'Saladette' suffered the least reduction in vitro pollen germination, but had the greatest loss in seed set at high temperatures. In their opinion, seed set is probably the most reliable method to measure gamete viability. They also found that 'CIAS16r and rS69161 had the least reduction in pollen viability using seed set as a criterion and ' P1262934' ovules suffered the least damage due to high temperature. Pollen viability was greatly reduced in 'PI-
262934' but ovule viability was less severely affected. In
'BL6807' ovule viability was more severely reduced than pollen viability.
Genetics of Heat Tolerance
Schaible (46) indicated that heat tolerance demonstrated by
'Porter' and 'Narcarlang' tomato cultivars is governed by a quantitative inheritance system, and is not tightly linked with genes which control undesirable traits such as small fruit size, poor color, and poor flavor. Shelby, Greenleaf, and Peterson (47) showed that heat fe rtility in a cross 'AU165' X ‘FloradeV was partially dominant. In their opinion, the high variances in this cross, particularly in the population, suggest that heat tolerance is subject to considerable environmental influence. They obtained relatively high broad sense heritability for heat tolerance coupled 17 with low narrow sense {additive genetic effect) heritability in this cross. They attributed these results to the effect of few genes involved.
Villareal and Lai (55) noted a continuous distribution of fruit setting score among the parents and different generations which suggested a fairly complex inheritance of heat tolerance. They found that while it was relatively easy to identify both extremes
(i.e., no fruit to light fruit vs. heavy fruit set), it was difficult to classify the intermediates. The heat-tolerant parents showed a preponderance of higher scores, whereas the non-heat-tolerant parents exhibited a preponderance of lower scores. Heritability values were generally low, ranging from 5 to 19%, which indicates that the greater proportion of variability was due to environmental causes. The low heritability of heat-tolerance is compatible with the observation that characters with the lowest heritabilities are those more closely connected with reproductive fitness, whereas, those characters with the highest heritabilities are those that are least important to reproduction.
El Ahmadi and Stevens- (14) conducted a complete diallel test using 5 cultivars with excellent high temperature tolerance and one California cultivar lacking stigma exsertion. They found that the cultivars differed genetically for number of flowers per cluster, percent fruit set, number of seeds per fruit and stigma exsertion. Recessive genes were found to be associated with greater 18 flower number at normal and high temperatures and heritability for this character was high. They also found that percentage fruit set was under the control of a largely additive gene system with a moderate heritability at high temperature. Non-all elic gene interaction was involved in seed set and dominance components exceeded additive effects at both temperatures. Heritability for seed set was low at high temperature. Stigma exsertion at high t temperature was controlled by partially dominant genes with a high dial 1 el additive component and heritability. They suggested that a scheme of selection for specific combining ability would be useful to combine the strength of the high temperature tolerant lines with needed characters from a successful cultivar.
Ovary Shape
Hanna, Abu-Baker and Imam (17) in their study on the inheritance of ovary shape in Cucumis melo found that the elongated slender ovaries showed partial dominance over the parent which had a higher ovary shape index. MATERIALS AND METHODS
The response of various components of the reproductive process
to high temperature in tomatoes was studied in three tests.
Eight tomato cultivars namely 'Saladette', 'BL6807', 'S6916',
1P1262934', 'Chico I I I ', ' CL9-0-0-11 , ' L401' and 'Floradel'
were used in this study. The first four cultivars were described
by El Ahmadi and Stevens (13) in their study of heat tolerance.
Information regarding some of the characteristics of the cultivars
is as follows:
'Sal adette*
A cultivar of determinate, compact growth habit with moderately
seeded red fruits that are 4.4-5.7 cm in diameter. It was bred
by Paul W. Leeper for production in the lower Rio Grande Valley
of Texas.
■BL6807'
A selection bred at Beaver Lodge, Alberta, Canada. Plants
are small, open and determinate in growth habit. It has compound
inflorescense and produces fruits 3.4-4.5 cm in diameter. This
selection gave the highest fruit set when tested with other lines
at a constant temperature of 26.7°C by Charles and Harris (8).
'Chico III'
A processing determinate cultivar that produces pear shaped
fruits. The fruit weighs approximately 45-63 grams. This cultivar
was developed by the Texas Experiment Station and it*shows some
heat tolerance. 19 20
'S6916'
According to Charles and Harris (8), ' S69161 is 'Narcarlang' and was the same material that Schaible (46) used in his studies.
It is determinate in growth habit, branches and produces flower clusters rather profusely. The fruits are pink because of the colorless skin, relatively heavily seeded and about 3.4-4.5 cm in diameter. 'Narcarlang' was found to set fruit abundantly at
26.7°C night temperature by Schaible (46).
■CL9-0-Q-r
A cultivar obtained from AVRDC breeding program in Taiwan.
It is a determinate cultivar that produces a small to medium size fruit (30-45 grams in weight) and it shows heat tolerance.
■L40r
Early determinate cultivar developed by the L.S.U. Experiment
Station breeding program. It is heat susceptible, produces red fruits that weigh 110-127 grams.
'Floradel'
Indeterminate cultivar released by Florida Experiment Station.
It is a recommended cultivar for Louisiana and shows no heat tolerance. It produces fairly large fruits weighing approximately
140 grams.
'P1262934'
This is the cultivar 'MalintkaloV of the U.S.S.R. obtained from the North Central Regional Plant Introduction Station at 21
Ames, Iowa. Lorenze of Oklahoma reported in the Northeastern
Regional Plant Introduction Station report of February 1973 that it has the capacity to set fruits at high temperature. The plants are determinate, medium size with red fruits and 4.2-4.9 cm in diameter.
Test 1 - Germplasm Experiment
In the firs t experiment six tomato cultivars namely: 'Saladette',
‘BL6807’ , 'Chico I I I ', 'S6916', 1CL9-0-0-1' and 1L4011 were grown in the Summer of 1978 and Spring of 1979. Each tomato cultivar was compared in both seasons for the following characters:
1. Percentage of fru it set
2. Percentage of flower drop
3. Percentage of dormant or undeveloped ovaries
4. Fruit weight in grams
5. Seed number per fru it
6. Average weight of 100 seeds
7. Percentage of germinated seeds, and
8. Percentage of non-aborted or normal pollen grains
The seeds of each cultivar were planted in the greenhouse in commercial jiffy-mix media. Approximately two weeks after germination or when the firs t true leaf had developed, the tomato seedlings were potted in 2h inch peat pots. The seedlings were allowed to grow for three or more weeks before transplanting to the field.
They were transplanted in the first week of June for the summer 22 planting and the second week of March for the spring planting.
A randomized complete block design with four replications and seven plants per plot was used in both summer and spring tests. Each plot was 122 cm wide and 4.2 m long and plants within each plot were spaced 61 cm apart.
The plants were left to grow without pruning or staking.
Normal cultural practices were followed and the soil was fertilized before transplanting with 90 kg each of N, p2°5s and K2° per *iec'tare* Six clusters of flowers on each plant were tagged using different color tags to facilitate detection. The tagging process continued for three weeks in each season. Only the three base flowers on each cluster were used and the rest were removed. The tagging process was done only when the three base flowers were opened. Fruit set, flower drop, and dormant ovaries were recorded at least a week after the opening of each flower and the percentage of fru it set, flower drop, and dormant ovaries were calculated for each plant on approximately 18 flowers per plant.
Pollen grains were collected from ten flowers on each tomato cultivar at random in the first week of July in the summer and the third week of April in the spring. Two slides with pollen were prepared from each cultivar using the technique followed by Alexander (2) for staining pollen grains to differ entiate between aborted and non-aborted pollen and the per centage of non-aborted (normal) pollen was calculated. 23
Ten mature fruits were harvested at random from each cultivar
in each season. The fru it itself was considered the experimental
unit and weighed to the nearest gram and seeds were removed from
each fruit and counted. The average number of seeds per tomato
for each cultivar and also the simple correlation coefficient of
fru it weight and seed number were calculated. Seeds were dried
in room temperature for several days. Four sets of 100 seeds of
each cultivar were weighed in grams and the average weight of 100
seeds was recorded.
In the seed germination test 400 seeds of each tomato cu lti
var grown in the summer and spring were divided into four repli
cations of 100 seeds each and planted equally spaced in wet paper
towels and placed in an incubator according to the rules of testing
seeds described in the Journal of Seed Technology (3). The early
germinated seeds in each cultivar were counted on the sixth day
after planting. The late germinated seeds were counted on the
eleventh day after planting. The percentage of the total germinated
seeds for each cultivar in each season was calculated.
A computer analysis program was used to determine various
statistical constants and measurements for this study.
Test 2 - Dial!el Experiment
Seven tomato cultivars, 'L401', 'Chico I I I 1, 'Floradel',
'PI262934', 'S69161, 'Saladette', and 'BL6807', were used as parents
in a partial dial lei cross. All possible crosses excluding the 24 reciprocals were made between these tomato cultivars in the green house. Seed of the 21 crosses generated by this dial lei test were planted in the greenhouse in the second week of May 1978 using the same procedures as in the first study. The data for fruit set, flower drop and dormant ovaries were recorded and the percentage of each of these categories was calculated. The maximum and minimum daily temperatures during the month of July was recorded on a hygro-thermograph. Plot means were calculated for all traits and analysis of variance was performed on data for each character.
Analysis of combining ability was performed according to Griffing's
Model 1, Method 4 (16). In Griffing's Model 1 all effects are fixed and the experimental material is the population about which inferences are made. Method 4 includes one set of F^'s but neither parents nor reciprocal Fj's were used. In this case there are
P(P—1)/2 different F^ mean values. Estimates of variance components were calculated for each source of the combining ability analysis of variance with appropriate algebraic manipulation of terms com prising the expected mean squares. The components in their general terms are presented as follows: 0 EG.* Variance component for general combining ability = p_-|- ■ O 5* V * Variance component for specific combining ability = p(p_ 3 ) where is the general combining ability (GCA) effect of the i— parent, S.. is the specific combining ability (SCA) effect for the ^ 3 cross between the i— and j— parent. 25
Test 3 - Study of Morphological Abnormalities of Flowers, Fruit Set and Inheritance of Stigma and Style Diameter and Ovary Shape
,L40I' a large round fruited type was crossed with 'Chico III'
to study the above characters. The parents were selfed and crosses
were made in the greenhouse during 1977 and 1978 to produce F^,
F2 and first backcross generation seeds. The seeds of the parents
and each generation were planted in the greenhouse using the same
procedure as the first experiment. Seedlings were transplanted
in the field during the summer in the first week of June 1978
using a complete randomized block design with four replications.
Also the two parents were grown in Spring 1979 to compare the
flower morphology of these two cultivars in the summer and spring
seasons. In the spring the plants were seeded in the greenhouse
in February and transplanted to the field in the middle of March.
Six flower clusters on each plant were tagged using only the three
base flowers of each cluster for this study. At the time of tagging
the morphological characters of each flower such as the elongated
style and the splitting of the antheridial cone were recorded.
Fruit set, flower drop and dormant ovaries were recorded on the six clusters of each plant at least one week after anthesis on parents and other filial generations in the summer.
In the middle of the flowering season and after the tagging process was over, one flower from each tomato plant, usually the firs t flower on the seventh cluster was removed just before, anthesis.
The calyx and corolla of each flower were removed and the stigma 26 diameter, style diameter, ovary length and ovary diameter were measured using an ocular micrometer divided into 0.05 mm scale under a dissecting microscope. Ovary shape index was determined by dividing ovary diameter by ovary length and multiplied by 100.
Flowers with no sign of style elongation or antheridial cone sp lit were classified as normal flowers and the others were classi fied as abnormal.
In studies on the mode of inheritance of stigma diameter, style diameter and ovary shape, several procedures were followed to determine the type of dominance, nature of gene action, number of effective genes and degree of heritability.
1. Dominance
The nature of dominance was evaluated by comparing the expected arithmetic mean with observed mean for the F2» backcross (BC) to 'L4011 and 'Chico I I I '. The formula used for the calculation of the theoretical arithmetic mean for different populations were those mentioned by Powers and Lyon (40) and Powers et a l . (41).
Population Arithmetic Mean
F1 F1+ V 2 F2 (Pj + P2 + 2 ^ / 4
BC/L401 (Pj + Fx)/2
BC/Chico III (P2 + F1)/2
Where: = observed mean of the female parent
P2 = observed mean of the male parent
Fj = observed mean of the F^ population 27
The difference between the observed and the arithmetic means
for each population was statistically tested applying the "t"
tpsttest Ofot significance<;ianifiranrp ac as follow.;- follows, t t - standard°-b-se rv e d erroiTof mean - arithmetic observed mean mean. The agreement between the observed and the arithmetic means
of a given population indicates absence of dominance. Cases where
the observed mean of a given population lies between its arithmetic
mean and the observed mean of one of the parents would indicate t its partial dominance. Complete dominance is expected when the
observed mean of the is not significantly different from the
mean of one of the parents. Heterosis is encountered when the
observed mean exceeds that of the higher parent or lower than
the lower parent.
Another measure of the degree of dominance was made by deter mining the relative potency of gene sets. This measure is based on the ratio between the genetic value of the F^ heterozygote to
the genetic value of either parent. The formula used for determining
potency was: F^ - M.P./^fPg + P^)
Where: M.P. is the average of the two parents
P^ is the parent with smaller value
P? is the parent with larger value, Wigan (59) and Mather (34).
A value of 1 indicates dominance and a value of 0 indicates no dominance. Skewness was calculated by the computer. A (t) test of significance was applied to the measure of skewness as follows: t= sk V 6n(n-l)/(n-2)(n+l)(n+3) 28
A positive skewness indicates an excess in the number of items smaller than the mean; whereas, the negative skewness indicates an excess of items larger than the mean.
2. Nature of gene action:
The nature of gene action was determined by comparing the expected means of the F^, F2> backcross to'L40r and backcross to
'Chico IIP populations on the basis of arithmetic gene action with the observed mean of each population. The expected arithmetic mean of each population was calculated according to Powers et a l. (41).
Arithmetic gene action assumed that the effects of individual genes upon the genotype are additive.
3. Number of genes controlling the difference between parents:
Two formulas were used to obtain estimates of the number of effective factors as follows:
(A) Castle-Wright formula; Castle (7) N - ■"8(s2F2-s2'r1r° 2 Where: N = minimum number of genes
D = the difference between the two parental means 2 s F^ = variance of F^ generation 2 s F2 = Variance of F2 generation
The formula assumes the following:
a - equal effect of genes involved
b - additive gene action
c - absence of dominance
d -maximum range exists between parents
e - one parent contributes only genes with plus effects and the other parent only genes with minus effects 29
(B) The Wright formula; Burton (5)
N = 0.25(0.75-h+h2)D2 S2f2-S2f j
Where: h = P2"P1 n = minimum number of genes in which the parents differed
P^ = mean of one parent
P2 = mean of the other parent
Fj = mean of the generation o s F^ ~ variance of the F^ generation 2 s F2 = variance of the F2 generation
The assumptions on which this formula is based are:
a - no linkage between pertinent genes
b - one parent supplies positive factors and the other parent supplies negative factors
c - all genes are equal in their contribution
d - the degree of dominance of all dominant factors is the same
e - no interaction exists between pertinent non-all elic genes
4. Heretability:
Heretability i.e. the measure of relative magnitude of genetic and non-genetic variance is calculated as the ratio of heritable variance to the total variance. Heritable variance includes the dominance, epistatic and additive genetic variances; and the total variance includes these plus environmental variance, Here tability was calculated as follows: Where: VF2 - variance of the Fg
VE = environmental variance
Two estimates of the environmental variance*(VE) were used in the present investigation. These were:
First estimate = Fj variance, VF^; Burton (5) t Second estimate = Arithmetic mean of the two parental variances Frey et al. (15) EXPERIMENTAL RESULTS
The responses of various components of the reproductive organs
of the tomato to the effect of high temperatures were studied in
three tests.
Test 1 - Germplasm Experiment
In this test six tomato cultivars were grown in the Summer
of 1978 (high temperatures) and Spring of 1979 (normal temperatures)
and several characters were studied.
In Table 1 is shown the weekly minimum, maximum and mean temper
ature during a 13 week period in Summer 1978 and Spring 1979. The minimum temperature in the Summer of 1978 ranged from 22.6°C to
25.3°C and the maximum temperature ranged from 32.4°C to 36.1°C.
The mean temperature ranged from 27.7°C to 30.5°C. For the Spring
of 1979 the minimum weekly temperature ranged from 8.3°C to 19.6°C
and the maximum ranged from 20.0°C to 30.3°C. The weekly average -
for this period ranged from 14.2°C to 24.8°C.
In Figure 1 is shown the minimum, maximum and mean daily temper
atures for the first four weeks in July of 1978 when all data for
the summer season were recorded. The daily minimum, maximum and mean range of temperature during this period was 21.1-26.7°C,
27.8-36.7°C and 24.4-31.7°C, respectively.
Fruit Set
Data in Table 2 show the mean fruit set expressed as a per
centage of the total number of flowers studied. In the spring season
fru it set ranged from 93.3% in 'Saladette* to 78.1% in ,L401* and 31 38 MAXIMUM 36 34
MEAN
3 0 -
MINIMUM 26 24 22 20
2 4 6 8 10 12 14 16 18 20 22 24 26 28 DAYS OF JULY
Figure 1. Daily maximum, minimum and mean temperature for July 1-28, 1978. 33
this was the only significant difference.
In the summer season fru it set percentage was lower for all cultivars, however 'BL68071 gave the highest percentage (50.5) differing significantly from any other cultivar. 'CL9-0-0-11»1S6916* and 'Saladette' set relatively high percentage of fruits (33.6, 29.5 and 28.6 respectively) with no significant difference among them. t 'Chico III' set 11% and 'L401' was the most severely affected cultivar with a fru it set of 1.2%.
A thorough investigation of the morophological structure of the flowers of 1L4011 during the summer of 1978 and the spring of
1979 seasons revealed that 53.1% of the total flowers formed in the summer had elongated style and/or split antheridial cone (abnormal), while 46.9% were of normal structure. In the spring 89.2% of the flowers were normal and 10.8% had elongated styles and/or split antheridial cones. 'Chico III' had 99.6% and 98.8% normal flowers in the spring and the summer seasons, respectively as shown in Table 4. The elongation of style and the split of antheridial cone expose the stigma and style to hot sun and dry wind causing damage to them before pollination; therefore, reducing fruit set.
When percentage fru it set for each tomato cultivar was compared in both seasons, highly significant differences existed (Table 3); however, some cultivars were more severely affected than others.
'BL68071 was the most tolerant while 1L4011 was the most severely injured. Other cultivars with relatively good fru it set in summer of 1978 were 'CL9-0-0-T, 'S6916' and 'Saladette'. 34
Flower Drop
In comparing the six tomato cultivars for flower drop the data showed highly significant differences occurred among them in both the
Summer of 1978 and Spring of 1979 as shown in Table 5. 'L40r had
22.8% of its flowers to drop in the spring and 36.1% in the summer.
'Chico I I I 1 dropped 8.5% of its flowers in the spring and 42,9% in the summer. 1BL6807* had the lowest flower drop percentage in both seasons and 'Saladette' ranked second to the lowest.
Highly significant differences on percentage flower drop occurred for each cultivar between seasons with the exception of 'BL6807' as shown in Table 6.
In general these data show that high temperature had a large effect on increasing the number of dropped flowers in the summer, however different cultivars responded differently.
Dormant or Undeveloped Ovaries
The tomato cultivar 'L401' had the highest amount of dormant ovaries (6%) in the spring and 62.8% in the summer and 'Saladette' had the second highest percentage with 5.9% and 54.1% for the spring and summer, respectively. 'CL9-0-0-V had the lowest percentage of dormant ovaries in both seasons as shown in Table 7,
Each tomato cultivar showed large differences between spring and summer seasons in the percentage of dormant ovaries Table 8.
In general all cultivars had a small percentage of dormant ovaries in the spring but much larger in the summer. 'L40T had a large number of dormant ovaries and was not significantly different from 'Saladette'. These dormant ovaries did not develop and could 35
not be considered tomato fruits.
In general, data shown in Tables 2 to 8, indicate that fruit setting ability, flower drop, and dormant ovaries expressed as per centages are characteristic of the tomato cultivars and the high temperature had a great effect on reducing the number fruit set.
'BL6807', 'CL9-0-0-V, ' S69161 and 'Saladette' set the highest per centage of fru its under hot summer conditions in this experiment whereas 1L401' was seriously affected and to some extent 'Chico II I'.
Fruit Weight
As shown in Table 9 mean fruit weight of six tomato cultivars ranged from 22.2 to 127.4 grams in the spring season and from 16.1 to 109.5 grams in the summer and differences among cultivars in both seasons were highly significant. 'L4011 produced the largest fru its; whereas, 'S6916' had the smallest fruits. 'Saladette' ranked second in fruit size in the summer and third in the spring. There were no differences in fru it size between 'Saladette1 and 'Chico III' in the spring but they were significantly different in the summer. In comparing the fru it weight of each cultivar between seasons (Table 10) a highly significant difference existed between the spring and the summer seasons for the cultivars 'L40V, 'Chico III' and 'CL9-0-0-1,
The average fruit weight was approximately the same in both seasons for 'Saladette', 'BL6807' and 'S6916'. These data suggest that high temperature reduced fru it size in certain tomato cultivars while others showed no differences. 'Saladette', 'BL6807' and 'S6916* performed equally well at high and cooler temperatures. 36
Seed number
As shown in Table 11 mean seed number per fru it varied sig
nificantly among tomato cultivars in both the spring and summer
seasons. 'L401' had the highest average seed number per fruit in
both seasons. 'Chico I I I 1 had the lowest mean number of seeds per
fru it in the spring and 'BL6807* had the lowest number in the summer.
Data in Table 12 show a comparison of each cultivar for mean seed
number per fruit under the two different seasons and significant
differences were found between the two seasons for all tomato cultivars with the exception of 1CL9-0-0-11 and ‘Chico I I I 1 which showed no
differences.
The simple correlation coefficient between fru it weight and
seed number for each of the six tomato cultivars was highly signifi
cant in the spring and the summer seasons with the exception of 1L401' which was only significant as shown in Table 13.
Seed Weight
The mean weight in grams of 100 seeds varied significantly among tomato cultivars in both seasons with 'Saladette' having the heaviest seeds in both seasons and '56916* had the lightest or smallest seeds as shown in Table 14.
A comparison of each cultivar between the two seasons revealed a highly significant difference 1n the mean weight of 100 seeds for
'L401' and 'Chico III*. The seed weight between seasons for 'Saladette1,
'CL9-0-0-T, 'BL6807' and 'S6916' was significantly different at the
5% level of probability as shown in Table 15. 37
In general the mean weight of TOO seeds of each cultivar was
lighter in the summer than in the spring with 'L40V and 'Chico III'
showing the greatest reduction as shown in Table 14.
Percentage of Germinated Seeds
As shown in Table 16 germination of seeds from the tomato cultivars grown in the spring season was higher than those from the same cultivars in the summer season. 'S69161, ' CL9-0-0-11 and
'Chico III1 gave statistically the highest percentage seed germin ation and 'BL6807' gave the lowest. In the summer seed germination from cultivars 'S6916', 'CL9-0-0-11 and 'Saladette1 were comparable and 1BL68071 had the lowest seed germination.
Data in Table 17 show a comparison of each cultivar for seed germination between seasons. 'Saladette' gave comparable percentage of seed germination in both seasons. 'S6916' was significantly different and the other cultivars were different at a highly signifi cant level.
Stained Pollen Grains
Data in Table 18 show the percentage of stained pollen grains from flowers of six tomato cultivars grown in summer of 1978 and spring of 1979 seasons. All cultivars had a high percentage of normal or stained pollen grains ranging from 89,1# for 'Saladette' to a high of 96.6# for ' BL68071 in the spring. In the summer 'BL6807' had the highest percentage (94#) of stained pollen and 'L401', S6916' and 'Chico III' had a comparable percentage of stained pollen of
87.6, 86.7 and 86.3#,respectively. The cultivars 'CL9-0-0-1* and
'Saladette' had the lowest percentages of stained pollen of 73.9 and 38
51.4%, respectively in the summer.
As shown in Table 19 only 'BL6807' and ' L401' showed no significant differences in the percentage of stained pollen between seasons. All other cultivars had highly significant differences. Table 1. Weekly minimum, maximum, and mean temperature (C) during a 13 week period in Summer 1978 and Spring 1979.
Summer 1978 Spring 1979
Minimum Maximum Mean Minimum Maximum Average Date temperature temperature temperature Date temperature temperature temperature
6/5-6/11 22.9 32.4 27.7 2/26-3/4 10.2 20.4 15.2 6/12-6/18 22.6 33.0 27.8 3/5-3/11 8.3 20.0 14.2 6/19-6/25 24.3 35.6 29.9 3/12-3/18 11.6 • ^ 21.9 16.8 6/26-7/2 24.1 36.1 30.1 3/19-3/25 12.8 23.5 18.1 7/3-7/9 25.3 • 35.5 30.5 3/26-4/1 17.1 26.1 21.6 7/10-7/16 25.2 35.7 30.4 4/2-4/S 13.8 24.3 19.1 7/17-7/23 23.9 33.6 28.7 4/9-4/15 17.7 27.7 22.7 7/24-7/30 23.9 34.1 29.0 4/16-4/22 19.0 26.2 22.6 7/31-8/6 24.2 36.1 30.2 4/23-4/29 17.6 26.3 22.0 8/7-8/13 23.6 33.5 28.5 4/30-5/6 19.6 26.8 23.2 8/14-8/20 24.1 35.7 29.8 5/7-5/13 19.4 30.3 24.8 8/21-8/27 24.2 35.0 29.6 5/14-5/20 19.4 28.8 24.1 8/28-9/3 23.5 33.6 23.6 5/21-5/27 16.0 27.1 21.6
CO VO 40
Table 2. A comparison of mean percentage fru it set of six tomato cultivars in two seasons.
Spring (1979) Summer (1978)
Cultivar % fruit set* Cultivar % fruit set*
Saladette 93.3 a 8L6807 50.5 a
BL6807 92.9 ab CL9-0-0-1 33.6 b
Chico III 86.2 ab S6916 29.5 b
S6916 83.3 ab Saladette 28.6 b
CL9-0-0-1 82.5 ab Chico III 11.0 c
L401 78.1 b L401 1.2 d
* Percentages within season followed by different letters are significantly different. Duncan's multiple range test, 5% level.
Table 3. Statistical comparison of each of six tomato cultivars between seasons for mean percentage fruit set.
Spring (1979) Summer (1978) Seasonal differences
Saladette Saladette **
BL6807 BL6807 **
Chico III Chico III
S6916 S6916 **
CL9-0-0-1 CL9-0-0-1 **
L401 L401 **
** Significant at 1% level 1
41
Table 4. Mean percentage normal flowers for tomato cultivars in two seasons.
Tomato cultivar Spring (1979)* Summer (1978)**
Chico III 99.6 98.8
L401 89.2 46.9
* Significnat at 5% level
** Significant at 1% level
Table 5. Mean percentage flower drop for each of six tomato cultivars in two seasons.
Spring (1979) Summer (1978)
Cultivar % flower drop* Cultivar % flower drop*
L401 22.8 a CL9-0-0-1 43.9 a
S6916 12.7 b Chico III 42.9 a
Chico III 8.5 be L401 36.1 a
CL9-0-0-1 7.9 bed S6916 26.7 b
Saladette 7.5 cd Saladette 17.3 c
BL6807 1.9 d BL6807 5.2 d
* Percentage within season followed by different letters are significantly different. Duncan's multiple range test, 5% level. 42
Table 6. Statistical comparison of each of six tomato cultivars between seasons for mean percentage flower drop.
Spring (1979) Summer (1978) Seasonal differences
L401 L401 +*
S6916 S6916
Chico III Chico III **
CL9-0-0-1 CL9-0-0rl **
Saladette Saladette **
BL6807 BL6807 n.s *
** Significant at 1% level n.s. Not significant
Table 7. Mean percentage dormant ovaries for each of six tomato cultivars in two seasons.
Spring (1979) Summer (1978)
Cultivar % dormant ovaries* Cultivar % dormant ovaries
L401 6.0 a L401 62.8 a
Saladette 5.9 a Saladette 54.1 ab
Chico III 5.4 a Chico III 46.1 be
BL6807 5.3 a BL6807 44.3 c
S6916 4.0 a S6916 43.8 c
CL9-0-0-1 2.7 a CL9-0-0-1 22.5 d
* Percentages within season followed by different letters are significantly different. Duncan's multiple range test, 5 % level. 43
Table 8. Statistical comparison of each of six tomato cultivars between seasons for percentage dormant ovaries.
Spring (1979) Summer (1978) Seasonal differences
L401 L4Q1 **
Saladette Saladette **
Chico III Chico III **
BL6807 BL6807 **
S6916 S6916 **
CL9-0-0-1 CL9-0-0-1 **
** Significant at 1% level
Table 9. Mean fru it weight for each of six tomato cultivars in two seasons.
Spring (1979) Summer (1978) Mean fruit Mean fru it Cul tivar weight, grams* Cultivar weight, grams*
L401 127.4 a L401 109.5 a
Chico III 63.3 b Saladette 53.9 b
Saladette 59.3 b Chico III 44.8 c
CL9-0-0-1 45.4 c CL9-0-0-1 29.8 d
BL6807 27.0 d BL6807 20.9 e
S6916 22.2 d S6916 16.1 e
* Percentages within seasons followed by different letters are significantly different. Duncan's multiple range test, 5% l e v e l . 44
Table 10. Statistical comparison of each of six tomato cultivars between seasons for mean fruit weight.
Spring (1979) Summer (1978) Seasonal differences
L4Q1 L401 **
Chico III Chico Iir **
Saladette Saladette n.s.
CL9-0-Q-1 CL9-G-Q-1 **■
BL68Q7 BL6807 n.s.
S69I6 $691$ n.s.
** Significant a t 1% Tevel n.s. Nat significant
Table 11. Mean number of seed per fru it for each of six tomato cultivars in two seasons.
Spring (1979) Summer (1978) Mean Mean no. seed no. seed Cultivar per fruit* Cultivar per fruit*
L40I 90.9 a L401 73.0 a
S6916 89.9s a CL9-0-0-1 67.7 a
BL68Q7 81.7 a S6916 60.5 ab
Saladette 78.6 a Chico III 52.2 b
CL9-Q-Q-1 58.1 b SaTadette 48.5 b
Chico III 50.4 b BL6807 24.2 c
* Percentages within seasons followed by different letters are significantly different. Duncan's multiple range test, 5% level. 45
Table 12. Statistical comparison of each of six tomato cultivars between seasons for mean number of seeds per fruit.
Spring (1979) Summer (1978) Seasonal differences
L401 L401 *
S6916 S6916 **
BL6807 BL6807 **
Saladette Saladette **
CL9-0-0-1 CL9-0-0-1 n.s.
Chico III Chico III n.s.
* Significant at 5% level
** Significant at 1% level n.s. Not significant
Table 13. Simple correlation coefficient between fru it weight and seed number within each of six tomato cultivars for two seasons.
Spring (1979) Summer (1978) Correlation Correlation Cultivar coefficient Cultivar coefficient
BL6807 0.65** BL6807 0.67**
Chico III 0.71** Chico III 0.46**
CL9-0-0-1 0.78** CL9-0-0-1 0.49**
L401 0.57** L401 0.36*
Saladette 0.81** Saladette 0.44**
S6916 0.68** S6916 0.72**
* Significant at 5% level
** Significant at 1% level 46
Table 14. Mean weight of 100 seeds for each of six tomato cultivars in two seasons.
Spring (1979) Summer (1978) Mean weight Mean weight Cultivar grams* Cultivar grams*
Saladette 0.41 a Saladette 0.38 a
L401 0.39 b Chico III 0.29 b
Chico III 0.35 c L401 0.28 b
CL9-0-0-1 0.29 d CL9-0-0-1 0.27 b
BL6807 0.25 e BL6807 0.23 c
S6916 0.21 f S6916 0.19 d
* Percentages within seasons followed by different letters are significantly different. Duncan's multiple range test, 5% level.
Table 15. Statistical comparison of each of six tomato cultivars between seasons for mean weight of 100 seeds.
Cultivar Cultivar (Spring 1979) (Summer 1978) Seasonal difference
Saladette Saladette ■k
L401 L401 **
Chico III Chico III **
CL9-0-0-1 CL9-0-0-1 •k
BL6807 BL6807 *
S69I6 S6916 *
* Significant at 5% level
** Significant at 1% level 47
Table 16. Percentage of seed germination for each of six tomato cultivars in two seasons.
Spring (1979) Summer (1978) Mean % Mean % Cultivar germination* Cultivar germination*
S6916 100.0 a S6916 96.0 a
CL9-0-0-1 99.5 a CL9-0-0-1 93.0 a
Chico III 97.5 a Saladette 92.5 a
L401 94.3 b Chico III 82.5 b
Saladette 93.8 b L401 70.8 c
BL6807 65.0 c BL6807 52.8 d
* Percentages within seasons followed by different letters are significantly different. Duncan's multiple range test, 5% level
Table 17. Statistical comparison of each of six tomato cultivars between seasons for percentage of seed germination.
Spring (1979) Summer (1978) Seasonal differences
S6916 S6916 *
CL9-0-0-1 CL9-0-0-1 **
Chico III Chico III **
L401 L401 **
Saladette Saladette n.s.
BL6807 BL6807 **
* Significant at 5% level
** Significant at 1% level n.s. Not significant 48
Table 18. Percentage of normal pollen grains for each of six tomato cultivars in two seasons.
Spring (1979) Summer (1978) Mean (%) Mean (%) Cultivar stained pollen* Cultivar stained pollen*
BL6807 96.6 a BL6807 94.0 a
Chico III 96.5 a L401 87.6 b
S6916 94.2 ab S6916 86.7 b
L401 92.1 b Chico III 86.3 b
CL9-0-0-1 90.8 b CL9-0-0-1 73.9 c
Saladette 89.1 b Saladette 51.4 d
* Percentages within seasons followed by different letters are significantly different. Duncan's multiple range test, 5% level.
Table 19. Statistical comparison of each of six tomato cultivars between seasons for percentage of normal pollen.
Spring (1979) Summer (1978) Seasonal differences
BL6807 BL6807 n.s.
Chico III Chico III **
S6916 S6916 **
L401 L401 n.s.
CL9-0-0-1 CL9-0-0-1 **
Saladette Saladette **
** Significant at 1% level n.s. Not significant 49
Test 2 - Diallel Experiment
The performance of 21 F^ hybrids from seven tomato parents crossed in all possible combinations excluding the reciprocals were evaluated for fruit set, flower drop and dormant ovaries during a period of four weeks in July 1978.
Data in Table 20 show that the mean percentage fruit set for the 21 hybrids ranged from 18.1% in the cross
1L401' X 'Saladette' to 67*2% in the cross 'Chico III* X
1S6916'. As shown in Table 21 for analysis of variance for percentage fru it set the F^ value for genotypes (hybrids) was significant. These genotypes were investigated by analysis for combining ability, in which variation of Fj hybrids was partitioned into general combining ability (GCA) and specific combining ability (SCA). The evaluation of variance components revealed that the variances for general combining ability for fruit set were 36 times larger than the components for specific effects. These additive gene effects for fruit set under hot weather conditions were more important than their non-additive effects.
The greatest relative general effect for fruit set was observed for the tomato parent ' S69IS' as shown in Tables 20 and
22 indicating that this parent has good general combining ability therefore is expected to do well in most hybrid combinations.
’B16807' had the next highest positive value for general combining 50 ability. 'L401' had the lowest value indicating that this tomato cultivar consistently depressed fruit set in the Fj but 1S69161 transmitted substantial fruit set to its progeny followed by 'BL6807' as shown in Tables 20 and 22.
Flower Drop
Mean percentage flower drop of the 21 Fj hybrids is presented in
Table 23. The cross 1S69161 and ‘BL68071 gave the lowest flower drop of 3.1% whereas the cross 1L401r and 'FloradeV gave the highest flower drop of 62.7%.
Cross variance showed highly significant differences as shown in Table 24 indicating that the 21 F^ hybrids differed significantly for flower drop. Mean squares for both general and specific combining ability were highly significant (Table 24). The GCA/SCA variance component ratio was 13:1 indicating that additive genetic effects were considerably more important than non-additive genetic effects for flower drop. Significant SCA effects suggest that non-additive gene effects also contributed to the variation expressed for this character.
Data in Table 25 show the general and the specific combining ability values for the seven parents and the 21 crosses. 'BL6807' was the parent that gave the lowest percentage of flower drop in its progenies.
It has the greatest negative value for the GCA of 18.48 while 'FloradeV consistently transmitted substantial amounts of flower drop ability to its progeny (Table 25). 'FloradeV gave the highest possitive general combining ability for flower drop (19.39%). 'S6916' which gave the highest general combining ability for fruit set, ranked second to ' BL6807' in the lowest GCA for flower drop (-10.60). These data 51
show the importance of 'BL6807' and *S69161 tomato cultivars for
low flower drop or abscission which is a very undesirable character
in tomato production under summer conditions.
Dormant Ovaries
Data in Table 26 show mean percentage of dormant ovaries for
each of 21 F^ hybrids. The percentage dormant ovaries ranged from
9.05£ in the cross 'Floradel' X *P12629341 to 67.8% in the cross
1L401 X ' BL6807'. Progenies from the breeding parent ' S69161 had
the lowest percentage of dormant ovaries followed by ‘Floradel*.
*BL6807' had a large number of dormant ovaries in its progenies.
The analysis of variance among the 21 F^ hybrids- and the GCA and
SCA showed a highly significant F ratio as shown in Table 27;
however, the ratio of the general combining ability to the specific was almost 12:1. This is a good indication that the additive gene effect controlling the dormancy of ovaries is more important than
the other types of gene action i.e. dominance and epistatic effect.
The GCA for each tomato parent and the SCA for each specific cross are shown in Table 28. The lowest general combining ability for this character was found in 1S6916r. This parent was most effective in transmitting the characters associated with low number of dormant ovaries. 1S69161 had a GCA of -18.22 which was followed by 'Floradel' with -15.75 and the ' PI262934' with -1.06. ' BL6S07' gave the highest GCA for dormant ovaries (16.86) and it was followed
by 'Chico I I I ’ with 6.18 then 'Saladette' with 6.04 and ' L401' with
6 . 00. 52
In general 1S69161 transmitted good fruit setting ability to its progenies while it depressed flower drop and dormant ovaries.
1BL68071 was the next best parent for transmitting fruit setting ability and less flower drop, however, it transmitted the character for dormant ovaries to its progenies. Table 20. Mean percentage of fruit set of tomato hybrids in a dial!el test of seven parents.
Parent Chico III Floradel PI262934 S6916 Saladette BL6807
L401 20.1 18.7 19.3 63.1 18.1 25.9
Chico III 36.1 23.2 67.2 24.6 34.9
Floradel 34.1 55.7 30.0 33.4
PI262934 59.2 30.6 36.8
S6916 57.9 65.8
Saladette 37.4
BL6807 54
Table 21. Analysis of variance of 21 F, hybrids for percentage fru it set.
Source df t MS F
Hybrids 20 . 7125.67 31.00**
Blocks 3 78.80 0.34 g X b 60 345.24 1.50
Error 442 229.83
GCA 6 872.51 81.39**
SCA 14 23.91 2.23*
Error 442 10.72
GCA:SCA ratio = 81.39:2.23 = 36:1 *Significant at 5% level
**Significant at 1% level Table 22. General and specific combining ability of seven tomato parents in a dial lei test for percentage of fruit set.
Parent Chico III Floradel PI262934 S6916 Saladette BL6807 GCA
L4Q1 -1.40 -3.12 -1.55 9.17 -1.86 -1.24 -12.19
Chico III 6.14 -5.83 4.99 -3.54 -0.36 -4.06
Floradel 4.64 -6.91 1.50 -2.24 -3.66
PI262934 -2.45 3.03 2.16 -4.63
S6916 -2.80 -1.97 28.51
Saladette 3.67 -5.55
BL6807 1.58 •
SE(Gi) ±1.36
SE(Si j ) ±2.67 Table 23. Mean percentage of flower drop of tomato hybrids in a diallel test of seven parents.
Parent Chico III Floradel PI262934 S6916 Saladette BL6807
L401 27.5 62.7 49.0 15.9 34.4 6.4
Chico III 37.7 22.1 18.4 29.7 18.8
Floradel 56.9 30.7 42.9 31.6
PI262934 27.8 31.0 6.6
S6916 17.6 3.1
Saladette 6.6
BL6807 57
Table 24. Analysis of variance of 21 F, hybrids for percentage flower drop.
Source df MS F
Hybrids 20 6652.23 30.92**
Blocks 3 207.08 0.96 g X b 60 483.14 2.25
Error 442 215.17
GCA 6 750.13 74.71**
SCA 14 59.41 5.91**
Error 442 10.04
GCA:SCA ratio = 74.71:5.91 = 13:1
**Significant at 1% level Table 25. General and specific combining ability of seven tomato parents in a dial1 el test for percentage flower drop.
Parent Chico III Floradel PI262934 S6916 Saladette BL6807 GCA
L401 -4.04 9.57 9.60 -7.50 1.25 -8.87 6.22
Chico III -7.08 -8.96 3.31 4.89 11.90 -2.13
Floradel 4.28 -5.92 -3.47 2.60 19.42
PI262934 4.89 -1.68 -8.13 5.72
S6916 0.84 4.35 -10.25
Saladette -1.85 -0.50
BL6807 -18.47
SE(Gi) ±1.31
SE(Sij) ±2.59 Table 26. Mean percentage dormant ovaries of F. tomato hybrids in a diallel test of seven parents.
Parent Chico III Floradel PI262934 S6916 Saladette BL6807
L401 52.4 18.6 31.9 20.9 47.4 67.8
Chico III 26.2 54.7 14.5 45.7 46.4
Floradel 9.0 13.6 27.1 35.6
PI262934 13.0 38.4 56.6
S6916 24.6 31.1
Saladette 55.9
8L6807 60
Table 27. Analysis of variance of 21 hybrids for dormant ovaries.
Source df MS F
Hybrids 20 6372.46 32.87**
Blocks 3 283.93 1.46 g x b 60 497.75 2.57
Error 442 193.88
GCA 6; 815.99 90.16**
SCA 14 69.03 7.62**
Error 442 9.05
GCA:SCA ratio - 90.16:7.62 = 12:1
**Signifleant at 1% level Table 28. General and specific combining ability for seven tomato parents in a diallel test for percentage of dormant ovaries.
Parent Chico III Floradel PI262934 S6916 Saladette BL6807 GCA
L401 5.43 -6.47 -7.91 -1.70 0.57 10.09 6.00
Chico III 0.96 14.77 -8.28 -1.34 -11.53 6.18
Floradel -8.96 12.84 1.99 -0.35 -15.76
PI262934 -2.47 -1.37 5.95 -1.06
S6916 1.97 -2.34 -18.27
Saladette -1.81 6.04
BL6807 16.86
SE(Gi) ±1,25
SE(SiO) ±2.46 62
Test 3 - Study of Morphological Abnormalities of Flowers, Fruit Set and Inheritance of Stigma and Style Diameter and Ovary Shape
The cross *L401 X 'Chico III' and the subsequent generations, were used to study the following:
1. Morphology of flowers of plants of parents and progenies
for normal versus abnormal flowers (flowers with split
antheridial cone and stylar exsertion).
2. Percentage fruit set of parents and progenies.
3. Stigma diameter inheritance.
4. Style diameter inheritance.
5. Ovary shape inheritance.
The two characters of normal flowers and fruit set are associ ated with heat tolerance, and the three characters of stigma and style diameter and ovary shape relate to the success of the field and hand pollination of cultivars and shape of fruit produced.
Normal Flowers
As shown in Table 29 the mean percentage of normal flowers produced in the summer by '1401' was 46.9% ± 3.78 by 'Chico III* it was 98.8% ± 0.58. The population had a mean of 91.4% + 1.55.
The progenies from the F£, backcross to 11401' and backcross to
'Chico III' had mean values of 81.2 ± 1.22, 72.1% ± 1.75 and
90.4% ± 1.41, respectively. The coefficient of variability was higher for 'L4011 and its backcrosses. In Figures 2 and 3 are shown the normal and abnormal flowers, respectively. . 63
Figure 2. Normal flowers produced by ‘Chico III' (left) and 1L4011 (right) in the summer season. 64
Figure 3. Abnormal flowers produced by ‘L40X' in the summer season. 65
The mean of the two parents differed significantly at the one percent level of probability. A comparison between the F^ generation mean and each of the two parental means showed that highly significant differences existed in both cases; however the mean of 91.4% was closer to the 'Chico III' mean of 98.8%. The means for normal flowers for the Fg generation and the backcross to 'Chico I I I 1 were also high.
The backcross to the 1L401' parent had a comparatively low percentage of normal flowers. These data suggest that the ability of the two parents to produce normal flowers in the summer is under a heritable mechanism showing a partial dominance of 'Chico II I'.
Data in Table 30 show the mean percentage of normal flowers produced by 'L4011 and 'Chico I I I 1 in the spring. 'Chico III* produced 99.6% normal flowers, whereas 1L401' produced 89.2%, The two parents differed significantly;however,the margin was not as great as in the summer (Table 29).
Fruit Set
Data in Table 31 show a summary of the mean percentage of fruit set of the parents, F^, Fg and backcross generations of a cross
'L4011 X Chico III' in the Summer of 1978. The mean percentage fru it set for ' L401' was 1.1% and for 'Chico III' i t was 8.1% and they were highly significantly different. The Fj generation had 10.6% fruit set and the Fg generation dropped to 4,6%. The backcross to ‘L401* and to 'Chico III* gave 2.8% and 15.2% fru it set, respectively.
These data indicate in general that fruit setting ability is under 66 genetic control with some dominance of the relatively high fruiting ability of Chico III. In this study the variation due to environ mental effects was large and Chico III is not considered a very heat tolerant parent as found in this study.
Inheritance of Stigma and Style Diameter and Ovary Shape
The. mode of inheritance of stigma and style diameter (Figure 4) and ovary shape was studied in the cross 'L40I1 X'Chico III'.
t Stigma Diameter
In Table 32 is shown' the distribution of plants of the parents and progenies for the cross 'L401' X 'Chico III'into classes for stigma diameter. There are 11 classes and each class represents an increment in stigma diameter of .07 mm. Also shown in this table are the means, variance and coefficients of variability of the parents and progenies. The stigma diameter of flowers of'L401'ranged from
0.80 to 1.20 mm with a mean of 1.00 ± 0.02 mm, whereas'Chico III' ranged from 0.45 to 0.70 mm with a mean of 0.55 ± 0.01 mm. In the F^ stigma diameter ranged from 0.50 to 0.85 mm with a mean of
0.65 ± 0.02 mm. The plants in the Fg generation showed a frequency distribution of flower stigma diameter from 0.45 to 1.10 mm having a mean of 0.67 ± 0.01. Plant distribution for stigma diameter in the backcross to 1401' ranged from 0.50 to 1.15 mm with a mean of
0.75 ± 0.01, whereas stigma diameter of the plants in the backcross to 'Chico III'ranged from 0.40 to 0.90 mm with a mean of 0.59 ± 0.01.
Data in Table 33 indicate that the stigma means of the two parents were significantly different at the 1% level of probability. Figure 4. 0.401' (left) and 'Chico III' (right) tomato f 1owers showing the stigma, style and ovary after removing the calyx and corolla. 68
The difference between the observed and the expected arithmetic means of the population was highly significant indicating the
presence of some dominance. This was supported by the data from
the Fg and backcross to '1.401'. The observed F^ mean differed
significantly from the means of both parents, however, it was skewed towards the mean of the smaller parent. Potency ratio was -0.52 indicating partial dominance of the smaller stigma.
A highly significant positive skewness for the Fg and the backcross to'Chico III1 parent or small stigma diameter was found. These data support the partial dominance of the smaller stigma. The minimum number of genes controlling this character as determined by Castle-Wright formula (7) was 2.97 and by Wright formula (5) it was 3.38, therefore indicating a minimum of three pairs of genes controlling stigma diameter.
Data in Table 34 indicate that heritability of stigma diameter ranged from 40.2% to 49.4% depending on the method used indicating that the environment has a considerable effect on the expression of this character.
Style Diameter
In Table 35 is shown the distribution of plants of the parents and progenies for the cross'L401'X'Chico III'into classes for style diameter. There are II classes and each class represents an increment in style diameter of 0.07 mm. Also shown in this Table are the means, variance and coefficient of variability of the 69 parents and progenies. The style diameter of flowers of 'L4011 ranged from .80 to 1.10 mm with a mean of 0.89 ± 0.02 mm, whereas
'Chico III'ranged from 0.25 to 0.35 mm with a mean of 0.31 ± 0.01 mm. In the F^, style diameter ranged from 0.40 to 0.65 mm with a mean of 0.48 + 0.01 mm. The plants in the Fg generation showed a frequency distribution of flower style diameter from 0.25 to 1.00 mm having a mean of 0.49 ± 0.01. Plant distribution for style diameter in the backcross to 'L401' ranged from 0.35 to 0.95 mm with a mean of 0.57 ± 0.01, whereas style diameter of the plants in the backcross to 'Chico III'ranged from 0.25 to 0.65 mm with a mean of 0.39 ± 0.01.
Data in Table 36 indicate that the style diameter means of the two parents were significantly different at the 1% level of probability.
The difference between the observed and the expected arithmetic means of the F^ population was highly significant indicating the presence of some dominance. The mean differed significantly from the means of the two parents, however it was closer to the smaller parent indicating the partial dominance of the smaller parent style. This also was confirmed with a potency ratio of
-0.39
Fg, backcross to'L401'and backcross to'Chico III1 populations were positively and significantly skewed which is again in support of the partial dominance of the parent with smaller style diameter.
The minimum number of genes controlling this character as determined by Castle-Wright formula (7) was 2.94 and by Wright (5) 70
it was 3.17 therefore indicating a minimum of three pairs of
genes controlling style diameter.
Data in Table 37 indicate that heritability of style diameter
ranged from 72.8% to 74.4/5 depending on the method used. Such a
high value of heritability would indicate a rather small environ
mental effect on this character.
Ovary Shape The frequency distribution for ovary shape index of plants of the
parents, F^, Fg and backcross generations is shown in Table 38.
There were 11 classes for ovary shape index having increments of
7 units per class. Ovary shape index in'L4011 ranged from 100-140 with a mean of 123.9 + 1.8 whereas that in'Chico III' ranged from
68-92 with a mean of 79.0 ± 1.3. In the F^ plants, ovary shape
index ranged from 81-110 with a mean of 96.9 ± 1.3. Ovary shape
index in the Fg ranged from 55-133 with a mean of 94.6 ± 1.1. The data indicate the greatest variation in the Fg generation.
As shown in Table 39 the means of the two parents were signi
ficantly different at the 1 % level. There were significant differences
between the observed and the theoretical means for the Fp Fg and
the two backcrosses. The observed F^ mean for ovary shape index differed significantly from the means of the two parents and it was closer to the smaller parent. Potency ratio was -0.20. These data indicate that the elongated slender ovary shows weak partial dominance and this was supported by the skewness values of the Fg 71 and the backcross to'Chico III'populations. The minimum number of genes controlling this character, as determined by the two formulas (5), (15) was 1.35 and 1,38 or one pair of genes.
As shown in Table 40 the two estimates of heritability ranged from 72.8% to 80.7%. Such a high value of heritability indicate a rather small environmental effect on this character. Table 29. Mean percentage of normal flowers, standard error and coefficient of variability of parents, F^, F,, and backcross generations of the cross L401 X Chico III in Summer of 1978.
Generation No. plants Mean % normal flowers Standard Error CV {%)
L401 27 46.9 3.78 41.98
Chico III 24 98.8 0.58 2.88
28 91.4 1.55 8.99 Fi 234 81.2 1.22 32.90 F2 BC/L401 113 72.1 1.75 25.77
BC/Chico III 102 90.4 1.41 15.71
Mean Difference Comparisons
L4Q1 vs. Chico III **
L401 vs. F1 **
Chico III vs. Fx **
** Significant at 1% level 73
Table 30. Mean percentage of normal flowers produced by L401 and Chico III tomato cultivars in Spring (1979).
Tomato cultivar Mean*
L401 89.2'
Chico III 99.6
* Significant at 5% level 74
Table 31- Mean percentage fruit set of parents and progenies of the cross L401 X Chico III in the Summer of 1978.
Generation 0 Plants Mean % fru it set
L401 27 1.1
Chico III 24 8.1
28 10.6 Fi 4.6 F2 234 BC/L401 113 2.8
BC/Chico III 102 15.2
Mean Difference Comparisons
L401 vs. Chico III **
L401 vs. Fx **
Chico III vs. Fj n.s.
** Significant at 1% level n.s. Not significant Table 32. Frequency distribution of plants, mean, variance and coefficient of variability for stigma diameter in parents and progenies in the cross: L401 X Chico III.
Class ranges in mm
.40- .48- .56- .64- .72- .80- .88- .96- 1.04- 1.12- 1.20- Generation .47 .55 .63 .71 .79 .87 .95 1.03 1.11 1.19 1.27 N X Variance CV (3)
L401 2 10 4 9 1 1 27 1.00+0.02 0.0101 10.07
Chico III 3 14 6 2 25 0.55±Q.01 0.0039 11.50
6 7 8 4 3 28 0.65±0.02 0.0088 14.42 F1 6 38 41 54 31 12 9 3 5 199 0.67±0.01 0.0174 19.65 F2
BC/L401 7 12 26 13 27 12 - 2 1 100 0.75±0.01 0.0162 17.05
BC/Chico III 6 47 13 26 3 4 1 . 100 0.59±0.01 0.0082 15.68 Table 33. Comparative stigma diameter (mm) for observed and theoretical means, mean difference, potency, skewness and minimum number of genes in the cross: L401 X Chico III.
Generation L401 Chico III BC/L401 BC/Chico III F1 F2
No. of observed plants 27 25 28 199 100 100
Observed mean (mm) 1.00a 0.55a ' ' 0.65 0.67 0.75 0.59
Arithmetic mean (mm) 0.77 0.71 0.83 0.60
Mean difference observed vs. arithmetic (mm) 0.12** 0.04** 0.08** 0.0ln‘S*
Potency -0.52
Skewness 0.93** 0.43** 0.69**
Minimum no. of genes (Cast!e-Wright formula) - 2.97
Minimum no. of genes (Wright formula) =3.38
a Means of parents are significantly different at the 1% level of probability ** Significant at 1% level n.s. Not significant 77
Table 34. Genetic and total variance of stigma diameter and heritability in the F9 generation of the cross: L401 X Chico III.
Method of Genetic Total Heritability calculation variance variance %
Formula - Burton (5) 0.0086 0.0174 49.4
Formula - Frey et a l . (15) 0.0070 0.0174 40.2 Table 35. Frequency distribution of plants, mean, variance and coefficient of variability for style diameter in parents and progenies in the cross: L401 X Chico III.
Class ranges in mm
.25- .33- .41- .49- .57- .65- .73- .81- .89- .97- 1.04- Generation .32 .40 .48 .55 .64 .72 .80 .88 .96 1.03 1.11 N X Variance CV {%)
L401 11 2 7 .4 3 27 0.89±0.02 0.0092 10.79
Chico III 17 8 25 0.31±0.01 0.0013 11.86
6 8 11 1 2 28 F1 0.43±0.01 0.0050 14.63 52 199 p2 19 24 52 19 20 9 2 1 1 0.49±0.01 0.0195 28.23 BC/L401 11 9 38 11 19 8 1 3 100 0.57+0.01 0.0160 22.24
BC/Chico III 24 44 11 16 4 1 100 0.39±0.01 0.0082 23.16 Table 36. Comparative style diameter {mm)for observed and theoretical means, mean difference, potency, skewness and minimum number of genes in the cross: L401 X Chico III.
Generation L401 Chico III BC/L401 BC/Chico III F1 F2
No. of observed plants 27 25 28 199 100 100
Observed mean (mm) 0.89a 0.31a 0.48 0.49 0.57 0.39
Arithmetic mean (mm) 0.60 0.54 0.69 0.40
Mean difference observed vs. arithmetic (mm) 0.12** 0.05** 0-12n'S- 0.01n' s*
Potency -0.39
Skewness 0.74** 0.77** 0.78**
Minimum no. of genes (Castle Wright formula) = 2.94
Minimum no. of genes (Wright formula) =3.17 a Means of the two parents are significantly different at the 1% level of probability
** Significant at 118 level n.s. Not significant 80
Table 37. Genetic and total variance of style diameter and heritability in the generation of the cross: L401 X Chico III. c
Genetic Total Method of calculation variance variance Heritability %
Formula - Burton (5) 0.0145 0.0195 74.4
Formula - Frey et a l . (15) 0.0142 0.0195 72.8 Table 38. Frequency distribution of plants, mean, variance and coefficient of variability for ovary shape index in parents and progenies in the cross: L401 X Chico III.
Class ranges for indexes of ovary shape X 100)
55- 63- 71- 79- 87- 95- 103- 111- 119- 127- 135- Generation 62 70 78 86 94 102 HO 118 126 134 141 N X Variance CV {%)
L40I 1 1 5 9 8 3 27 123.9*1.8 85.82 7.48
Chico III 2 13 6 4 25 79.0±1.3 40.37 8.05
2 F1 9 13 4 28 96.9±1.3 44.69 6.90 4 14 F2 9 35 28 46 34 18 10 1 199 94.6*1.1 231.66 16.09 BC/L401 7 18 38 15 16 5 1 100 101.4*1.1 112.82 10.47
BC/Chico 3 16 22 21 16 17 3 2 100 83.4*1.3 158.18 15.09 Table 39. Comparative ovary shape index data for observed and theoretical means, mean difference, potency, skewness and minimum number of genes in the cross: L401 X Chico III.
Generation L401 Chico III BC/L401 BC/Chico III F1 F2
No. of observed plants 27 25 28 199 100 100
Observed mean 123.9a 79.0a 96.9 94.6 101.4 83.4
Arithmetic mean 101.4 99.2' . 110.4 87.9
Mean difference observed vs. arithmetic 4.5** 4.6** 9.0** 4.5**
Potency -0.20
Skewness -0.25n*s‘ 0.50** 032n.s.
Minimum no. of genes (Castle-Wright formula) = 1.35
Minimum no. of genes (Wright formula) = 1.38
a Means of the two parents are significantly different at the 1% level of probability
** Significant at 1% level n.s. Not significant 83
Table 40. Genetic and total variance of ovary shape and heritability in the F„ generation of the cross: L401 X Chico III. *
Method of Genetic Total Heritability calculation variance variance %
Formula - Burton (5) 186.97 231.66 80.7
Formula - Frey et a l . (15) 168.57 231.66 72.8 DISCUSSION
The results of the present investigations indicate that fru it set in the six tomato cultivars studied ranged from 1.2% in tomato cultivar L401 to 50.5% in BL6807 under hot summer conditions. Under spring conditions fruit set ranged from 93.3% in 'Saladette'to 78.1% in'L401'. The results show that'BL6807',
'CL9-0-0-1', 'S6916'and'Saladette’were the most heat tolerant culti vars. 'Saladette' and'BL6807' had the lowest percentage of flower drop while 'CL9-0-0-1* had the lowest percentage of dormant ovaries.
There have been extensive studies on the effects of high temperature on fru it set in the tomato. Smith (48) reported a great increase in blossom drop by hot dry winds and low humidity.
Several research workers (1, 30, 46, 57) are in agreement that optimum temperature for fru it set is from 15-22°C. Stoner and
Otto (52) reported that'Chico III'set the highest percentage of fru it among the cultivars that he studied in a hot greenhouse.
'Chico III'under 1978 summer field conditions in this study set only 11% of the tomato flowers as compared to 50.5% for'BL6807'.
This supports the conclusion of Villareal and Lai (55) that the heat-tolerant genes are easily influenced by environment and heat-tolerant selections should be tested in as many locations and seasons as possible before any recommendations are made.
In this study the temperature conditions were ideal for heat toler ance studies since the maximum day temperatures did not drop below
84 85
32.4°C and the minimum night temperature did not drop below
22.6°C. Rudich et a l . (44) reported that fru it set of 12 c u lti vars from divergent sources under high temperature conditions of 39 ± 2°C day and 22 ± 2°C night ranged from 0 % to 22% while that of'Saladette'was between 56% and 60%. Levy et a l . (31) found that fru it set varied from 77.3% to 16.3% among seven tomato cultivars studied under high temperature conditions therefore indicating differences among cultivars in heat tolerance. Stevens and Rudich (51) reported that in both the U.S. and Israel 'Saladette' was heat tolerant. In this study'Saladette'was similarly found to be heat tolerant.
The pronounced differences among cultivars to the response of high temperature indicate that heat tolerant germplasm permits the breeding of tolerant cultivars and the study of the nature of the primary physiological process impeding fruit set.
The study of the mean fruit weight of the cultivars showed that 'Saladette', 'BL6807' and'S6916'each gave comparable fru it size in the Spring (1979) and Summer (1978) and no significant differences in weight occurred between the two seasons. 'L40T and'Chico III1, which showed low percentage of fruit set, produced significantly smaller fru it in the summer than in the spring. 'CL9-0-0-r which set a high percentage of fruits in the summer developed smaller fruits than in the spring. This shows that fru it weight is more greatly affected by hot summer conditions in some cultivars than in others. 86
The average seed number per fruit was also affected due to
the environmental conditions. A significant reduction was found
in the average seed number per fruit developed in the summer in
'L401', 'S69161, 'BL68071 and 'Saladette'. 'CL9-0-0-1' and 'Chico 11T showed no significant differences for this character between the two seasons. Since a significant correlation between seed number and
fru it weight was found, this may explain that high temperature affects seed set hence affecting fruit size.
The results show that high temperature affected the size of the fruits and reduced the average number of seeds per fru it in some cultivars. Some cultivars were affected more seriously than others. Several research workers (12, 21, 25, 54) found a good positive correlation between fru it size and seed number. El
Ahmadi and Stevens (13) found that Saladette tomato cultivar had the greatest loss in seed set at high temperature among cultivars tested. Shaible (46) found that fruit size decreased as night temperatures were increased and fruit seediness of each cultivar was related to its degree of heat tolerance. Johnson and Hall
(27) found a high degree of seedlessness was observed in con junction with a high temperature condition.
Pollen grain staining tests showed that'BL6807'had the highest percentage of stained or normal pollen grains showing no significant differences between seasons. In each of'Chico III','S6916','CL9-0-0-1* and 'Saladette' there was a significant difference between the number 87
of normal pollen grains in the spring and summer. 'L401* did not
show any difference. In general all cultivars produced less pollen
in the summer than in the spring.
El Ahmadi and Stevens (13) found that pollen production was
reduced in all tomato cultivars studied and there was a lack of
pollen dehiscense. Pollen viability was less reduced in'BL68071
than ovule viability. Several other research workers (27, 31, 47)
reported that reduction of the quantity and/or functionality of
the gametes contributed to low fruit set.
» The mean weight of 100 seeds was significantly less in the
summer than in the spring for all cultivars, however the reduction was greater for '1.401' and 'Chico III*. The high temperature apparently
affected not only the number of seeds but also the size or weight of seeds.
We can conclude from the data on heat tolerance that 'BL6807'
set the highest percentage of fruits in the summer (50.5%) whereas
L401 set only 1.2%. 'Saladette', 'S6916' and 'CL9-0-0-1' cultivars also showed heat tolerance shown by the fairly high percentage of
fruit set. 'Chico III'did not show an appreciable amount of heat tolerance in this study because it had only 11% fru it set which was significantly lower than other cultivars except 'L401'. Stoner and Otto (53) reported that 'Chico III'was heat tolerant but the results of this study show it to have only a small amount of heat tolerance; however, it did produce many normal flowers during the 88 summer. 'BL6807' gave 94% normal pollen in the summer, however seed number was reduced from 81.7 seed per fru it in the spring to
24.2 in the summer. This indicates that the ovules in the fru it of'BL6807'are relatively more sensitive to high temperature than its pollen. 'Saladette'had a significant reduction of normal pollen grains from 89.1% in the spring to 51.4 in the summer, and the seed set was reduced from 78.6 to 48.5 seeds per fru it, however seed r viability was not affected as shown by the germination test. This study shows that'Saladette'suffered great loss in seed set and
'BL6807'ovule viability was more severely reduced than pollen viability. El Ahmadi and Stevens (13) reported similar results.
The severe reduction of fruit set in'L401'under summer condi tions can be partially explained by the fact that 53.1% of the total number of flowers examined at the time of anthesis had exserted styles and/or split antheridial cones which exposed the style and the stigma to the adverse conditions of hot sun and wind. Levy et al. (31) found that splitting of the antheridial cone and style
* exsertion were among characters that contributed to low fruit set. Several other research workers (8, 27, 31, 43, 44, 49) mentioned that style elongation is an important factor in preventing fru it set. Kuo et a l . (29) concluded that poor fruit set at high temperature is not due to a single factor but the causes are many and diverse.
The cross 'L401' X 'Chico III' showed that the ability to produce flowers without style exsertion and/or split antheridial cones 89
(normal flowers) in plants of its different generations was under heri table michanism with some dominance for normal flowers.
The Genetics of Heat Tolerance
According to Hyman (18) GCA and SCA can generally be interpreted in terms of additive and non-additive genetic variance, respectively, and the partitioning of variation into these components gives a discription of the genetics of the population being studied. He r further reported that the type of genetic variance in the reference population indicates the type of breeding scheme that will maximize tr a it improvement. In this study the differences found among hybrids for all three characters of fruit set, flower drop and dormant ovaries were due to genes with additive effects, however the small but significant amount of non-additive variance present can not be overlooked.
The greatest relative GCA for fru it set was observed for the tomato parent S6916 indicating that i t is a good general combiner and may be expected to do well in most hybrid combinations. 'BL6807' had the next highest positive GCA for fruit set. 'L401' had the lowest value for GCA indicating that this tomato cultivar consistently depressed fruit set in Fj combinations. The lowest flower drop was found in the F^ progenies of 'BL6807' and 'S6916' was the next lowest, whereas 'FloradeV had the largest amount of flower drop. 'S6916'had the lowest amount of dormant ovaries as shown by its high negative
GCA. 90
The large highly significant GCA effects for precentage fruit set, and the lesser effects of SCA suggests that greater progress in improving fruit set can be acheived by utilizing breeding schemes which lend themselves to increasing the frequency of those genes that are primarily additive. The most efficient system of breeding would be one that permits the combination of desirable genes into a homozygous cultivar with good horticultural characters. Also the parents with high SCA for high fruit set could be used in producing tomato hybrids with heat tolerance.
In the study of the inheritance of fruit set using'Chico III*as a parent crossed with 'L401', the results showed that this character was under a heritable mechanism with some kind of dominance. Schaible
(46) indicated that heat tolerance in some tomato cultivars is governed by a quantitative inheritance system with no linkage to undesirable traits. El Ahmadi and Stevens (14) found that percentage fru it set was under the control of largely an additive gene system with moderate heritability at high temperature. Shelby et al. (47) showed that heat tolerance in the cross'Au 16S1 X'FloradeV was partially dominant and this character was subject to considerable environmental influence which was the case in this study. Villareal and Lai (55) found that heritability for heat tolerance in tomatoes was 5-19%.
For stigma diameter, style diameter and ovary shape, data in this study indicated a partial dominance of the small stigma diameter, style diameter and some dominance of the'Chico III'ovary shape. Heritability 91 for stigma diameter was 40.2 to 49-4%; for style diameter 72-3% to
74.4% and for ovary shape 72.8% to 80.7% indicating that the environ mental conditions had the greatest effect on the inheritance of stigma diameter. Three pairs of genes as a minimum controlled the inheritance of each of stigma diameter and style diameter. One pair of genes was found to differentiate the two parents for the ovary shape character. Hanna et a l . (17) found that elongated or oblong ovaries in melons (Cucumis melo) were partially dominant over the parent with higher ovary shape index. SUMMARY
The response of various components of the reproductive organs
of the tomato including fruit set to the effect of high temperatures
in the summer and normal conditions in the spring were studied in
several tests.
It was found that'BL6807',’CL9-0-0-r,'S6916'and'Saladette* were the
most heat tolerant cultivars having a fruit set in the summer of
50.5, 33.6, 29.5 and 28,6%, respectively. 'Saladette* and'BL6807* had
the lowest percentage of flower drop in the summer while'019-0-0-1'
had the lowest percentage of dormant ovaries. 'L401'was the most
heat susceptible cultivar followed by'Chico III'with a fru it set of
1.2% and 11%, respectively.
Fruit weight was affected by hot summer conditions in some culti
vars more than in others. 'Saladette1, 'BL6807' and 'S6916' had comparable
fru it size in the Summer of 1978 and Spring of 1979, however 'L401*
and 'Chico III' had lower fru it set and smaller fruit in the summer than
in the spring.
A sginificant reduction in the average seed number per fruit was
found in the summer in 'L401', 'S6916', 'BL6807'and 'Saladette'. ‘CL9-0-0-1’
and'Chico III'showed no significant differences between the two
seasons. A significant correlation between seed number and fruit weight within each cultivar was found in the summer and spring.
Pollen grain staining tests showed that 'BL6807' had the highest percentage of stained or normal pollen grains showing no significant
92 93
differences between the summer and spring seasons. In each
of 'Chico III1, *56916', 'CL9-0-0-1' and 'Saladette* there was more
normal pollen in the spring and a significant difference between
seasons occurred but not in'L401'. In general all cultivars
produced less pollen in the summer than in the spring.
The high temperature of the summer apparently affected
not only the number of seeds but also the size or weight of
seeds since the mean weight of 100 seeds was significantly
less in the summer than in the spring for all cultivars and
the reduction was greatest for'L401* and'Chico III'.
'Saladette'was the only cultivar which gave comparable per centage germination of seeds produced in each season. 'S69161 showed a significant reduction in germination and the other cultivars were reduced to a highly significant level.
The severe reduction of fruit, set in'L401'under surntier conditions can be partially explained by the fact that 53.1% of the total number of flowers examined at the time of anthesis had exserted styles and/or split antheridial cones which exposed the style and the stigma to the adverse conditions of the hot sun and wind. The cross 'L401' X 'Chico III' showed that the ability to produce flowers without style exsertion and/or split antheridial cones (normal flowers) was under a heritable mechanism with some dominance for normal flowers.
In a second test seven tomato cultivars; 'L401', 'Chico III',
'Floradel', 'PI262934', 'S6916', 'Saladette'and 'BL6807' were used as 94
parents in a partial dial1 el cross to study the GCA and SCA for
fruit set, flower drop and dormant ovaries in the 21 generations.
In this study the differences found among hybrids for all three characters were due to genes with additive effects with a small but significant amount of non-additive variance.
The greatest GCA for fru it set was found in the parent'S6916'
indicating that i t is a good general combiner and may be expected to do well in most hybrid combinations. 'BL6807* had the next highest positive GCA for fru it set. ’L401' had the lowest value for GCA indicating that this tomato cultivar consistently de pressed fru it set under high temperatures in F^ combinations.
The lowest flower drop was found in the F^ progenies of'BL68071 and 'S6916'was the next lowest, whereas 'Floradel' had the largest amount of flower drop. 'S6916' had the smallest percentage of dormant ovaries.
The large highly significant GCA effects of parents for percentage fru it set and the lesser effects of SCA suggests that greater progress in improving fru it set can be achieved by utilizing breeding schemes which lend themselves to increasing the frequency of those genes that are primarily additive.
In a third test a cross between 1401' and 'Chico III'and its
F^» ?2 anc* backcross progenies were used to study normality of flower development, fru it set and inheritance of stigma and style diameter and ovary shape.' The ability to produce normal 95
flowers and high percentage of fru it set in this cross appeared
to be under a heritable mechanism and'Chico III'was found to
transmit normal flowers and a relatively high percentage of
fruit set to the F^ and subsequent progenies. Although the
fruit set was highly significantly different between the two
parents i t was only 8.1% in'Chico III'as compared to 1.1% for 'L401*. t Data in this study for stigma diameter, style diameter and
ovary shape show a partial dominance of the small stigma diameter,
style diameter and some dominance of the'Chico III'ovary shape.
Heritability for stigma and style diameter and ovary shape was
40.2-49.4%, 72.8-74.4% and 72.8-80.7%, respectively, indicating
that environmental conditions had the greatest effect on the
inheritance of stigma diameter. Three pairs of genes as a minimum controlled the inheritance of each of stigma diameter and style diameter. One pair of genes was found to differentiate the two
parents for ovary shape.
The most heat tolerant cultivars in all of these studies were 'S6916' and '8L6807' and others found to have good tolerance were'CL9-0-0-1'and'Saladette'. 'Chico III'showed some heat
tolerance and 'L401' and 'Floradel' were most susceptible. LITERATURE CITED
1. Abdalla, A. A. and K. Verkerk. 1968. Growth, flowering and fruit-set of the tomato at high temperature. Neth. J. Agric. Sci. 16:71-76.
2. Alexander, M. P. 1969. Differential staining of aborted and non-aborted pollen. Stain Technology. 44:117-122.
3. Anonymous. 1978. Association of official seed analysts. J. Seed Technology. 3{3):55.
4. Bohning, R. H., W. A. Kendall and A. J. Linck. 1953. Effects of temperature and sucrose on growth and translocation in tomato. Amer. J. Bot. 40:150-153.
5. Burton, G. W. 1951. Quantitative inheritance in pearl m illet (Pennisetum glaucum). Agr. J. 43:409-417.
6. Calvert, A. 1964. Pollen viability, germination and tube growth in the tomato (Lycopersicon esculentum M ill.). A review of the literature. Rep. Glasshouse Crops Res. Inst. 1963, 131-142.
7. Castle, W. E. 1921. An improved method of estimating the number of genetic factors concerned in cases of blending inheritance. Science. 54:223.
8. Charles, W. B. and R. E. Harris. 1972. Tomato fru it set at high and low temperature. Canad. J. Plant Sci. 52:497-506.
9. Charles, D. R. and H. Smith. 1939. Distinguishing between two types of gene action in quantitative inheritance. Genetics. 24:34-48.
10. Coyne, D. P. 1968. Differential response of stylar elongation in tomatoes to soil moisture levels. Hort. Sci. 3:39.
11. Davis, R. M,, JR., P. G. Smith, V. H. Scheers and R. W. Scheurman. 1965. Independence of floral fe rtility and fru it set in the tomato. Proc. Amer. Soc. Hort. Sci. 86:552-556,
12. Dempsey, W. H. and J. E. Boynton. 1965. Effects of seed number on tomato fru it size and maturity. Proc. Amer. Soc. Hort. Sci. 86:575-581.
96 97
13. El Ahmadi, A. B. and M. A. Stevens. 1979. Reproductive responses of heat-tolerant tomatoes to high temperature. 0. Amer. Soc. Hort. Sci. 104:686-691.
14. and . 1979. Genetics of high-temperature fruit "set in the tomato. J. Amer. Soc. Hort. Sci. 104:691-696.
15. Frey, K. J ., M. C. Shekleton, H. H. Hall and E. J. Benne. 1954. Inheritance of niacin, riboflavin and protein in two oat crosses. Agr. J. 46:137-139.
16. Griffing, B. 1956. Concept of general and specific com bining ability in relation to diallel crossing system. Austral. J. Biol. Sci. 9:463-493.
17. Hanna, H. Y., M. A. Abu-Baker and M. K. Imam. 1972. In heritance of some economic characters in crosses between sweet melon and snake cucumber. M.S. Thesis (Vegetable Crops) Assiut University, Egypt, pp. 121.
18. Hayman, B. I. 1960. The theory and analysis of diallel crosses. Genetics. 45:155-172.
19. Howlett, F. S. 1962. Introductory remarks. Proc. Plant. Sci. Symp. Campbell Soup Co., 59-64.
20. Hussey, G. 1965. Growth and development in the young tomato. III. The effect of night and day temperatures on vegetative growth. J. Expt. Bot. 16:373-385.
21. Imanishi, S. and I. Hiura. 1975. Relationship between fruit weight and seed content in the tomato. J. Jap. Soc. Hort. Sci. 44:43-40.
22. Iwahori, S. 1965. High temperature injuries in tomato. IV. Development of normal flower buds and morphological abnormalities of flower buds treated with high temperature. J. Jap. Soc. Hort. Sci. 34:33-41.
23. ______. 1966. High temperature injuries in tomato. V. Fertilization and development of embryo with special refer ence to the abnormalities caused by high temperature. J. Jap. Soc. Hort. Sci. 35:379-384.
24. ______. 1967. Auxin of tomato fruit at different stages of its development with a special reference to high temperature injuries. Plant and Cell Physiol. 8:15-22. 98
25. Iwahori, S., and K. Takahashi. 1964. High temperature injuries in tomato. III. Effects of high temperature on flower buds and flowers of different stages of development. J. Jap. Soc. Hort. Sci. 33:67-74.
26. Johnson, S. P. and W. C. Hall. 1952. Vegetative and fruiting responses of tomato to high temperature and light intensity. Bot. Gaz. 114:449-460.
27. ______and . 1954. Parthenocarpy in the tomato. Proc. Amer. Soc. Hort. Sci. 63:329-332.
28. and . 1955. Further studies on vegetative and fruiting responses of tomatoes to high temperature and light intensity. Bot. Gaz. 117:100-113.
29. Kuo, C. G., B. W. Chen, M. H. Chou, C. L. Tsai and T. S. Tsay, 1979. Tomato fruit-set at high temperatures. 1st International Symposium on Tropical Tomato, pp. 94-108.
30. Leopold, A. C. and S. I. Frances. 1952. Physiological factors in tomato fru it set. Amer. J. Bot. 39:310-317.
31. Levy, A., H. D. Rabinowitch and N. Kedar. 1978. Morphological and physiological characters affecting flower drop and fruit set of tomatoes at high temperatures. Euphytica. 27:211-218.
32. Lipton, W. J. 1970. Growth of tomato plants and fruit production in high humidity and at high temperature. J. Amer. Soc. Hort. Sci. 95:674-680.
33. Liverman, J. L. and S. P. Johnson. 1957. Control of arrested fru it growth. Science. 125:1086-1087.
34. Mather, K. 1949. Biometrical Genetics. Dover Publications, Inc. pp. 158.
35. Moore, E. L. and W. 0. Thomas. 1952. Some effects of shading and parachlorophenoxy acetic acid on fruitfulness of tomatoes. Proc. Amer.Soc. Hort. Sci. 60:289-294.
36. Mullison, VI. R. and E. Mull ison. 1948. Effects of several plant growth regulators on fru it set, yield and blossom-end rot of six tomato varieties grown under high temperatures. Bot. Gaz. 110:501-505.
37. Nightingale, G. T. 1933. Effects of temperature on metabolism in tomato. Bot. Gaz. 95:35-57. 99
38. Osborne, D. J. and F. W. Went, 1953, Climatic factors influencing parthenocarpy and normal fru it-set in tomatoes. Bot. Gaz. 114:312-322.
39. Powers, L. 1942. The nature of the series of environmental variances and estimation of the genetic variances and the geometric means in crosses involving species of Lycopersicon. Genetics. 27:561-575.
40. and C, B. Lyon. 1941. Inheritance studies on duration of developmental stages in crosses within the genus Lycopersicon. J. Agric. Res. 63:129-148.
41. ______, F. Locke and J. C. Garrett. 1950. Partition- ing method of genetic analysis applied to quantitative characters of tomato crosses. U.S.D.A. Tech-Bull. 998.
42. Rick, C. M. 1978. The tomato. Scientific American. 239(2): 77-87.
43. Rick, C. M. and W. H. Dempsey. 1969. Position of the stigma in relation to fru it setting of the tomato. Bot. Gaz. 130: 180-186.
44. Rudich, J ., E. Zamski and Y. Regev. 1977. Genotypic variation for sensitivity to high temperature in the tomato: pollination and fru it set. Bot. Gaz. 138:448-452.
45. Saito, T. and H. Ito. 1967. Studies on the growth and fruiting in the tomato. IX. Effects of the early environmental condi tions and the cultural treatments on the morphological and physiological development of flowers and the flower drop. (I). Effects of night temperature, light intensity and fertility of bed soil. J. Jap. Soc. Hort. Sci. 36:55-65.
46. Schaible, L. W. 1962. Fruit setting responses of tomatoes to high night temperatures. Plant Sci. Symp. Campbell Soup Co. pp. 89-98.
47. Shelby, R. A., W. H. Greenleaf and C. M. Peterson. 1978. Comparative floral fertility in heat tolerant and heat sensi tive tomatoes. 0. Amer. Soc. Hort. Sci. 103:778-780.
48. Smith, 0. 1932. Relation of temperature to anthesis and blossom drop of the tomato, together with a histological study of the p istils. J. Agric. Res. 44:183-190.
49. Smith, 0. 1935. Pollination and life-history studies of the tomato, Lycopersicon esculentum Mill. N.Y. (Cornell) Agr. Exp. Sta. Mem. 184. 100
50. ______and H. L. Cochran. 1935. Effect of temperature on pollen germination and tube growth in the tomato. N.Y. (Cornell) Agr. Exp. Sta. Mem. 175.
51. Stevens, M. A. and J. Rudich. 1978. Genetic potential for overcoming physiological limitations on adaptability, yield, and quality in the tomato. Hort. Sci. 13:673-678.
52. Stoner, A. K. 1978. Breeding vegetables tolerant to environ mental stress. Hort. Sci. 13:684-686.
53. ______and B. E. Otto. 1975. A greenhouse method to evaluate high temperature setting ability in the tomato. Hort. Sci. 10:264-265,
54. Verkerk, K. 1957. The pollination of tomatoes. Neth. J. Agric. Sci. 5:37-54.
55. V illareal, R. L. and A. H. Lai. 1979. Development of heat- tolerant tomato varieties in the tropics, lst^ International Symposium on Tropical Tomato, pp. 188-200.
56. , and S. H. Wong. 1978. Screening for heat tolerance in the qenus Lycopersicon. Hort. Sci. 13:479-481.
57. Went, F. W. 1944. Plant growth under controlled conditions. II Thermoperiodicity in growth and fruiting of the tomato. Amer. J. Bot. 31:135-150.
58. ;______. 1945. Plant growth under controlled condi tions. V. The relation between age, light, variety and thermo periodicity of tomatoes. Amer. J. Bot. 32:469-479.
59. and H. M. Hull. 1949. The effect of temper ature upon translocation of carbohydrates in the tomato plant. Plant Physiol. 24:505-526.
60. Wigan, L. G. 1944. Balance and potency in natural populations. J. Genetics. 46:150-160, AUTOBIOGRAPHY
The author was born and lived throughout his formative years in El Minya, a small town on the Nile Valley of Egypt,
240 kilometers south of Cairo.
Educational background includes a Bachelor of Science degree in General Agriculture from The High Agricultural Institute of
El Minya, Egypt in 1963. Following a working period at the same institution, the author received a Master of Science degree in
Horticulture from Assiut University, Egypt in 1972. At this time, the author is a candidate for the degree of Doctor of Philosophy.
101 EXAMINATION AND THESIS REPORT
Candidate: Hanna Yacoub Hanna
Major Field: Horticulture
Title of Thesis: Genetic Study of Heat Tolerance; Size of Stigma, Style and Ovary in the Tomato, Lycopersicon esculentum
Approved:
Major Professor and Chairman
Dean of the Graduatfv School
EXAMINING COMMITTEE:
/. W On.
C rG rtfU l
Date of Examination:
April 18, 1980