time, they must have different genetic constitutions, because their selfed prog- Color in Tomatoes eny segregate differently. The second in- dication is that the parental types are re- covered in the second generation. Finally, inheritance of pigment differences in the third cross-yellow crossed with tangerine-the first generation is red, al- studied for true-color breeding though neither of the parents is red. Furthemore, red tomatoes also appear in the selfed progeny of the red first genera- J. A. Jenkins and G. Mackinney tion hybrid. This breeding behavior is explained by It is of practical importance to the The yellow tomatoes have low total assuming that the two mutant types-yel- tomato grower and processor that the to- content of carotenoid pigments which are low and tangerine-differ from the red mato or its product shall have a typical, predominantly yellow in color. In some varieties by two different and independent readily identifiable color associated with yellow tomatoes, small quantities of lyco- gene mutations-genes are those factors an accustomed standard for tomatoes. pene may be formed, which are found in which determine the heritability of char- The original tomato may have such a irregular pinkish patches of color through- acters, such as color. characteristic color, but the processed out the flesh. Each of the pure-breeding parental product may not. This is particularly true Most commercial tomatoes contain an varieties may be symbolized-with the in products containing a percentage of alkali-soluble yellow skin pigment which capital letter R representing a dominant oily or fatty nontomato ingredients, is noncarotenoid in nature. red gene, the small r representing a sub- where owing to extraction of a high pro- The flesh of fruits with yellow skins in ordinant or recessive red gene, T repre- portion of tomato pigments, the color of contrast to those with colorless skins do senting the dominant tangerine gene and the tomato fraction appears untypically not receive the same radiation even t representing the recessive tangerine orange. though exposed side by side to the same gene-as follows: red RRTT, yellow rrTT, A study of the inheritance of pigment sunlight. The presence or absence of skin tangerine RRtt. differences in the tomato has been ini- pigment can only be evaluated in pheno- tiated. types-visible characters-whose genetic Color Types Appearing In First Genera- Some of the wild species of tomato- constitutions are identical except for this tion Hybrids and Their Progeny native to Peru-have fruits which are one factor, a di5cult comparison to make. virtually devoid of carotenoid pigments. Three crosses are possible between the Cross genevotionFirst genorationSecond The green chlorophyll-containing fruit three colored types; red crossed with yel- F, r, assumes an off-white color as it ripens. low; red crossed with tangerine; and, Rod crossed It is possible that the ancestral form of yellow crossed with tangerine. with yollow Red Red,yellow Red crossed the cultivated tomato was similarly de- These were made, and a study of the wlth tangorine Red Red, tangorine void of pigment, in which case the com- first generation hybrids together with Yollow crossed Red, yollow mon red-fruited type must have appeared their selfed progeny indicates-in the first with tangerine Red and tangorino as a mutant from the unpigmented an- place-that the first generation hybrids cestor. Whether or not it is true that the are red regardless of the color of the par- The above table may be amplified to red-fruited tomato was derived from an ents. These reds all look alike and have show the genetic constitution of the dif- unpigmented ancestor, it is known that the same pigment content. At the same ferent types together with their expected the red-fruited form has produced two frequencies of occurrence. mutants, the yellow and the tangerine. Color Types Appearing in the First and It is clear from the table in column two These have been known for so long that Second Generation Hybrids of Three that the first generation hybrid of the place and time of origin are uncertain. Tomato Crosses cross of red with yellow received a gene R The three color types in the cultivated Parents Second generation F. from the red parent and a gene r from and tomato-the red, the yellow and the tan- first Genotype Phenotype the yellow parent. The fact that the first gerine-contain complex mixtures of fjeneration Expected (genetlc (visible generation-F1-hybrid has the genetic ybrlds F. frequency constitution) charnctsrd carotenoid pigments, and the formation constitution Rr with respect to these two of specific pigments in the three cases is red (RRTT) x genes, together with the fact that it is red responsible for the respective character- and differs in no observable way from the istic colors. red-colored parent RR indicate that one of The carotenoids are insoluble in water, the R genes is sufficient for the formation but dissolve readily in fat solvents. They of the red-colored fruits. range in color from deep red to pale yel- The R gene is said to be dominant over low, and they derive their name from the r, or in other words, two doses of the r characteristic pigments of the carrot, gene must be present before the yellow among which is carotene, the most im- color is expressed. The random recom- portant natural source, directly or in- tangerine (RRtt) ' 1 bination of the gene pair Rr in the forma- directly, of vitamin A. 2 tion of the second generation gives two The red-fruited tomatoes contain sev- 2 RRTt genetic types of reds: one RR, which eral carotenoid pigments, but by far the 4 RrTt J breeds true like the parent, and the other most abundant is lycopene, which gives Rr, which like the F1 will again segregate F, red (RrTt)-. 1 the tomato its characteristic red color and rrTT} -yellow in the ratio of three reds to one yellow in takes its name from the scientific name 2 rrTt the next generation. All tomatoes in this for the tomato, Lycopersicon. 1 RRtt )-tangerine first cross carried both dominant T genes. The tangerine tomato derives its color 2 Rrtt The same general comment applies from a closely related orange carotenoid .1 rrtt with respect to the other two hybrids. In pigment, prolycopene. Continued on next page

CALIFORNIA AGRICULTURE, FEBRUARY, 1951 13 TOMATOES 1:1,000. If necessary, the treatments may on the pseudobulb which turns at first a delicate yellow changing into orange red 'Continued from preceding page be repeated within a week or so. or red. The leaves finally drop off and the second hybrid-red crossed with tan- numerous orange red pseudobulbs can be gerine-only the Tt pair segregates, while Soft Rot seen in the pot. From the pseudobulb the all plants have both RR genes. Thus, the Soft rot of Cattleya orchids caused by organism migrates into the rhizome and T gene is dominant over the t gene. In the Erwinia carotovora is a rare disease. Its will travel from plant to plant. case of the third hybrid-yellow crossed advent is sudden and the results are devas- The disease is very infectious and re- with tangerine-both of the gene pairs tating. It is caused by the common soft quires immediate attention as soon as it segregate. rot bacterium-a soil inhabitant-which is first recognized. The control consists From a study of the three hybrids and attacks such crops as celery, carrots, and in applying 8-quinolinol or Natriphene their progeny, it is clear that at least potatoes. as for brown spot in Phalaenopsis. Sani- one R and one T is necessary for the for- The disease can start in fresh wounds tary measures must be observed and op- mation of the red carotenoid pigment, on Cattleya leaves and with high tempera- erators should disinfect their hands after lycopene. The precise role of these two ture and very high humidity it will handling infected Miltonias so as not to gene pairs in the formation of carotenoid rapidly change the leaf into a sack con- spread the disease. pigments is not entirely clear. There are taining liquefied tissues. The leaf wrinkles two uncertainties that will require further and droops. Later it breaks open and the Black Spot study. First, the double recessive rrtt has contents leak out. not yet been identified. Second, certain Plants affected by it can not be saved. The shippers of orchid blossoms also yellow tomatoes collected in Mexico are Control consists in early recognition of have troubles. Vanda blossoms shipped definitely anomalous. When collected, the disease and burning all the affected from a distance sometimes develop a they were classified as doubtful yellows. plants. The room in which the trouble oc- black spot right in the throat of the blos- When grown in Berkeley, they did not curred should be promptly and thoroughly sdm. Sometimes minute black spots scat- behave as pure yellow varieties, but were disinfected. tered on the petals of the flower ruin its consistently intermediate between red market value. The trouble is due to Gb- and yellow. merella sp., a fungus similar in its habits Independent studies carried on at Brown Rot to the gray mold fungus Botrytis cinerea Riverside suggest that three gene pairs Cypripediums are the only orchids in which sometimes attacks the flowers of determining pigment differences segre- California subject to the brown rot dis- Cattleya in greenhouses and in transit. gating in the species cross-Lycopersicon ease in orchid houses. It is caused by a Black spot infection of Vanda flowers esculentum crossed with L. peruvianum- bacterium, Erwinia cypripedii, which occurs before they are cut and shipped. When it reaches its destination the flower one of the green-fruited wild species. This prefers a temperature of 65' F or above fact together with the two uncertainties and a humidity of 70% or higher. begins to lose its color and black spots appear. The fungus develops slowly at mentioned indicate that only a beginning The disease is characterized by small to has been made in the study of inheritance medium-sized circular, somewhat greasy the low temperature prevailing in ship- ment but in the higher temperature of of tomato pigment differences. spots which, on running together, form the sales room the fungus grows and pro- J. A. Jenkins is Associate Professor in Ge- large sunken patches. The color varies duces the black spot. Black spot infection netics, University of California College of Agri- with the age of the lesion and in the culture, Berkeley. of Vanda blossoms has been prevented final stages is deep chestnut brown. The by the use of 8-quinolinol benzoate G. Mackinney is Professor of Food Tech- spots are frequently located close to nology, University of California College of Agri- 1:2,000 as a spray. This concentration of culture, Berkeley. the base of a leaf. Under favorable con- the chemical did not injure the appear- ditions the organisms migrate into the ance of the flowers. crown and thence into other buds causing death of all the living components of the Peter A. Ark is Associate Professor of Plant clump. To save plants already attacked Pathology, University of California College of ORCHIDS Agriculture, Berkeley. Continued from page 7 the treatment described above for brown spot of Phalaenopsis should be applied. The above progress report is based on Re- In full-grown plants the symptoms are search Project No. 973 being conducted by the . similar to those on seedlings. Infections Division of Plant Pathology. start on any part of a leaf but the most Bacterial Scorch dangerous location is at the base because Bacterial scorch and pseudobulb rot DECIDUOUS then the infection quickly moves into the has been observed recently on Miltonia Continued from page 12 growing point and the plant is doomed. Phalaenopsis plants of all ages are orchid hybrids. It is most severe under vail, a serious shortage could result. Such equally susceptible to the disease. conditions favorable for Miltonia grow- a shortage would undoubtedly give an up- In Cattleya brown spot is often con- ing-cool and moist greenhouses. ward boost to the price structure on fined to the upper part of the leaf. The The disease starts in wounds which are canned fruits all the way from the grower progress of the disease is not as rapid as always present on the brittle leaves of to the consumer. in Phalaenopsis. The lesion has well-de- Miltonia. The bacteria are exuded copi- With January and February tempera- fined margins and the color is nearer ously on the surface of the leaf and may ture playing a critical role in the final black than brown. The disease very sel- be spread by the water in syringing opera- outcome, it will be mid-March or early dom causes death in Cattleyas. tions from one pot to another, thus cre- April before accurate estimates of the Control of brown spot is achieved by ating an epidemic. situation can be made. By then the blos- the use of one part 8-quinolinol benzoate The affected leaves are water soaked som periods for most species will have to 2,000 parts of water or the sodium salt in early stages of the disease but later been reached or past and a real estimate of o-hydroxidiphenyl-Natriphene-also turn gray and even light brown and ap- of the fruit actually set can be made. pear scorched or blighted. Sometimes the at the rate of 1:2,000. In Cattleyas brown Dillon S. Brown is Assistant Professor of spot may be treated locally by swabbing disease is in the form of a narrow or wide Pomology, University of California College of it with a solution of corrosive sublimate, streak, terminating in the growing point Agriculture, Davis.

14 CALIF OR N I A' AGRICULTURE, FEBRUARY, 19 5 1