JOURNAL OF NEMATOLOGY VOLUME 8 JULY 1976 NUMBER 3

Morphological Variation in penetrans

RODRIGO TARTE and W. F. MAI ~

Abstract: Variability of morphological characters used to separate Pratylenchus penetrans from other species of the genus was studied in a population originating from a single gravid female. Pronounced heteromorphism was observed and characterized. About 30% of females had a crenate-tail terminus. Several shapes of styler knobs were characterized; 50% of them were anteriorly flattened to indented. The outer margin of the cephalic framework extended into the body from one-half to two annules. The shape of the spermatheca varied from round to oval. A fifth lateral line was observed in many specimens. Environmental factors, and particularly the host plant, influenced such morphometric characters as body length, width, esophagus length, stylet length, V value, a and b" ratios, as well as qualitative characters such as tail terminus, growth of ovary, and shape of median bnlb. reared on pea and cabbage had a higher percentage of females with a crenate-tail terminus than those from totnato, rye, beet, and alfalfa callus culture. Nematodes from peas were longer aml wider; they often had gonads that extended to esophagi, but they had shorter esophagi amt stylets than those from callus culture. Popula- tions from different geographical locations also exhibited variahility in morphological characters, as did the Cornell population. The validity of many characters used in species identification is discussed, and the possibility that other related Pratylenchus species are conspecific with P. pene- trans is suggested. Key Words: , crenate tail, smooth tail, host effect, selective response.

Knowledge of intraspecific variability of during development (4, 7, 9, 19). many morphological characters used in tax- Induced variability has been considered in onomy of plant-parasitic nematodes is often relation to population density (10), method lacking. As a result, the taxonomic value of of killing and fixation (13), environmental many such characters is doubtful, and factors (10), host species or growth medium proper identification is made very difficult. (1, 10, 11, 12, 14), and host physiology (3). Investigators concerned with morphological Differences related to geographical location variation have conducted research mainly have also been suggested in a few cases (17, on quantitative characters. The magnitude 29). of variations cannot be estimated unless de- The genus PratyIenchus contains ap- tailed studies on morphology and frequency proximately 40 described species, many of of variants, as they occur naturally within which differ only in small morphological different populations and as they are af- features, lntraspecific variation has been fected by ecological factors, are conducted. suggested by Taylor and Jenkins (30) and Naturally occurring, intraspecific varia- by Loo[ (19), and it has been carefully stud- bility in nematodes is considered in few tax- led by Roman and Hirschmann (25). No onomic reports and reviews (4, 5, 6, 15, 23, attempt has been made to study variability 25, 31). Variation has been associated with in living populations under a wide range of some aspects of nematode behavior (2, 4, 7, environments, or to determine the extent of 18, 22), as well as with changes occurring variability in different geographical popula- tions. Received for publication 9 September 1974. The present study was undertaken to de- 1Graduate Assistant and Professor, respectively, Department of Plant Pathology, Cornell University, Ithaca, New York termine tile extent of morphological varia- 14853. Present address of senior author, Facultad de Agl"on- tion in Pratylenchus penetrans (Cobb, 1917) omia, Universidad de Panama, Panama, R.P. The authors wish to thank the following persons for supplying cultures Filip. & Schuurm.-Stekh., 1941, especially of P. penetran.~: J. L. Townshend, Canada; D. C. M. with respect to those diagnostic characters Corbett, England; H. Inagaki, Japan; M. Oostenbrink, The Netherlands; N. D. Singh, Trinidad; A. C. Tarjan, used at the species level. The effects of dif- Connecticut; D. E. Stokes, Florida No. 1; A. J. Overman, ferent environments and the geographic Florida No. 2; G. Thorne, Kentucky; and K. R, Barker, North Carolina. source of populations were studied.

The JOURNAL OF NEMATOLOGY for April (8: 97-184) was issued 20 April 1976. 185 186 Journal of Nematology, I'olume 8, No. 3, July 1976 MATERIALS AND METHODS Variation of 8 quantitative and 10 qualitative and meristic characters, most of A population of P. penetrans originat- them commonly used in species differentia- ing in 1963 from a single gravid female was tion, was studied. Quantitative data were propagated on alfalfa callus tissue growing analyzed by the analysis of variance and by on modified ~Vliite's medium at approxi- Tukey's honestly significant-difference pro- mately 23 C in the dark (24). Extraction for cedure (THSD) at tlle 5% probability inoculation and microscopic observation level. Coefficients of variability were also was carried out by placing pieces of infected calculated. callus on a fiber filter supported by a screen in a shallow layer of water in a pie-pan. Cultures used were not necessarily of the RESULTS same age nor were they inoculated at the same time in the various experiments. CHARACTERIZATION OF VARIATION IN THE Additional fixed specimens of P. pene- CORNELL POPULATION OF P. penetrans: The trans were obtained for study from: The diagnostic characters of P. penetrans (28) Netherlands, Japan, Canada, Trinidad, consist of three lip annules, broadly England, and from the states of Maryland, rounded stylet knobs, lack of striations New York, North Carolina, Florida, Ken- around tile felnale-tail tip, round sper- tucky, and Washington of the U.S.A. matheca, short post-uterine branch, ovary not extending to esophagus, four lateral In experiments designed to determine lines, and outer margins of sclerotized labial the influence of environmental factors on framework extending posteriorly into the quantitative and qualitative characters, body about one body annule. Microscopic seeds of Wando peas, Pisum sativum L., observations of more than 500 females ob- were germinated in sterile sand and the tained from alfalfa callus tissue, however, seedlings transplanted 3 days later to 5-cm revealed extensive heteromorphism in most clay pots which contained a sandy loam characters. orchard soil (pH 6.7) with a low nitrogen Stylet knobs varied in shape from slop- and phosphorus content. Pratylenchus pene- ing anteriorly to being indented (Fig. 1), trans was then added by placing a suspen- with about 50% being anteriorly flattened sion of 500-1,000 nematodes close to the to indented. root tip of each seedling. One week after Female tails were usually rounded at the inoculation, intact soil balls were trans- tip, but truncated, pointed, or somewhat ferred to 20-cm clay pots where they re- clavate tails were also found. The tail mained for the duration of tlle experiment. terminus varied from smooth to distinctly Unless indicated otherwise, peas were re- crenate. About 30% of the nematodes planted twice during an experiment. No possessed coarsely annulated or crenate-tail fertilizer was applied except when the ef- tips in which one or more indentations, fect of nutrition was tested in a particular forming annules usually wider than the treatment. body annules, occurred at any point around At harvest, nematodes were extracted by the terminus but mostly toward the dorsal cutting the roots in pieces 1/2 to 1 cm long, side (Fig. 2). Coarsely annulated tail tips, blending them with water for 60 sec, pour- independent of number and location of ing the suspension on a paper filter, and indentations, were classified as crenate. collecting the nematodes after 48 h. When Crenate-tail tips, with one and two indenta- nematodes were extracted from soil, 100 ml tions oriented toward the dorsal side, were of soil were spread evenly over a fiber filter most common. The remaining 70% of the supported by a screen in a shallow layer of nematodes had typically smooth tails. Al- water and the nematodes collected after though, in some cases annulation continued 24 h. posteriorly on one side, it was never coarse, Adult females picked at random were and the tail tip was smooth. used in morphological observations. They The outer margin of the sclerotized were killed by being immersed in hot water cephalic framework occasionally extended (65 C) for 2 rain and fixed and mounted in from one-half to two annules posteriorly 2.5% formalin. on the body, but in most specimens, it Variation in P. penetrans: Tarte, Mat 187 MORPHO~fETRICS: Effects of host.--Ten ran- domized replicates of five host plants: 'Wand& pea (Pisurn sativum L.), rye (Secale cerale L.), 'Rutgers tomato' (Ly- copersicon esculentum Mill.), 'Round-up' cabbage (Brassica oleracea capitata L.), and 'Ruby Queen' beet (Beta vulgaris L.) were inoculated with a suspension of P. pene- trans and kept for 6 months in the gTeen- house at an average temperature of 21 C. After completion, 50 randomly picked fe- males fi'om each treatment were measured and studied. Treatments were compared ( ) ( with each other and with 50 females previ- ously preserved from the initial inoculum. Differences among treatments were found in body length, width, esophagus length, stylet length, and ratios a and b' (Table 1). The longest and widest nematodes were re- covered from peas, and the next longest (in descending order) were from the initial inoculum, rye, tomato, cabbage, and beet, respectively. The stylets in nematodes from all host plants were slightly shorter than the stylets in nematodes from the initial inocu- ltnn. Although esophagus length was about the same in nematodes reared on tomato and pea, tile b' ratio differed because of dif- ferences in body lengtla of the nematode in the two treatments. No differences were found in V. value. Observations of certain qualitative char- acters revealed that, in 30% of females FIG. 1. Shapes of stylet knobs found in the obtained from peas, the gonad extended Cornell University population of Pratylenchus pene- anteriorly to the esophageal glands, whereas trans cultured on alfalfa callus tissue. Top left to the same occurred in only 4% of those right: sloping anteriorly, broadly rounded, irreg- ularly rounded. Bottom left to right: flattened an- from tomato, and in none from the remain- teriorly, slightly indented, indented. ing treatments. A higher number of indi- viduals recovered from peas also had an extended about one body annule. The sper- almost round median bulb, in comparison matheca varied from round to oval and in with the oval median bulb from other treat- some cases was flattened. A fifth lateral line, ments. The percentage of crenate-tail present in the middle of the lateral field of females increased to 42% in peas and 59% some specimens, usually disappeared at the in cabbage. Many nematodes with stylet level of the vulva, No deviations from the knobs flattened anteriorly or indented were normal, 3-annule lip pattern were found. observed in all treatments. The median bulb was oval in most speci- Effects of feeding vs. storing without mens, although in a few cases it was nearly food.--A suspension containing 100 females round. The female gonad did not extend and 100 males was added to each of five anteriorly to the region of the esophageal replicates of: (i) Wando peas in 5-cm clay glands. The vulva region varied from non- pots; (it) sterilized soil in 5-cm clay pots; elevated to elevated with most females hav- and (iii) tap water in counting dishes. ing slightly elevated vulval lips. Treatments i and ii were maintained in a gTowth chamber at 21 C with a light in- INDUCED VARIATION IN MORPHOLOGY AND tensity of 21,520 lux (2,000 ft-c.) and a 188 Journal of Nematology, Volume 8, No. 3, July 1976

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~tt / /7 V FIG. 2. Types of tail tips found in the Cornell UniversityV population of Pratylenchus penetrans. Top row: Types of smooth-tail tips. Middle and bottom rows: Types of crenate-tail tips. Arrows indicate the three most common types of crenate tails. All tails are oriented laterally with the dorsal side to the left.

photoperiod of 12 h. Treatment iii was ered from pea roots were longest and kept in darkness in an incubator at 15 C. widest; the next (in descending order) were Three weeks after inoculation, the nema- from alfalfa callus, water, and soil, respec- todes were extracted from roots in treat- tively. In comparison with the stylets of ment i and soil in treatment ii, and 50 nematodes from inoculum, stylets of nema- females were picked at random from each todes from peas were shorter. Because of treatment and compared with the original longer body length of nematodes feeding on inoculum. Differences among treatments pea roots, their b' ratio was different from were found in body length and width; that of the nematodes from initial inocu- esophagus length; stylet length; and a, b', lum. The c ratio was higher in nematodes and c ratios (Table 3). Nematodes recov- feeding on peas than in other treatments.

TABLE 1. Effects of host plant on morphometric characters of females of Pratylenchus penetrans. ~

L Width Esophagus Stylet V a" b' c Treatment (#m) (#m) (#m) (tim) % (ratio) (ratio) (ratio)

Alfalfa callus 578.2 a 22.3 b 131,5 a 17.3 a 79.8 a 26.0 a 4.4 b 18.6 ab Peas 589.3 a 26.8 a 126,4 ab 17.0 ab 79.6 a 21 .I c 4.7 a 19.4 a Rye 522.0 b 21.3 bc 120.4 b 17.0 ab 80.1 a 24.7 ab 4.3 bc 18.8 ab Tomato 508.7 bc 20.9 c 125.6 ab 16.8 b 80.1 a 24.5 b 4.0 d 18.7 ab Cabbage 507.1 bc 20.3 c 121.6 h 16.9 ab 80.2 a 25.0 ab 4.1 cd 18.3 b Beet 489.0 c 20.6 c 122.4 ab 16.8 b 80.0 a 23.9 b 4.0 d 18.0 b Coefficient of variability % 7.16 10.23 12.81 4.55 1.83 9.75 8.66 9.86

*Treatment means with a letter in common do not differ, using Tukey's Honesty Significant Differences (P = 0.05). Variation in P. penetrans: Tarte, Mai 189 TABLE 2. Effects of host plant on qualitative morphological characters of Pratylenehus penetrans.

% females Alfalfa Character callus Peas Rye Tomato Cabbage Beet

Stylet (Lateral View) Sloping 4 18.2 4.3 11.4 4.2 3.3 Rounded 50 25.0 39.1 31.8 47.9 38.7 Flat. or indented 46 56.8 56.6 56.8 47.9 58.0 Median Bulb Oval 82 64.3 83.7 95.4 88.6 86.2 Almost round 18 35.7 16.3 4.6 11.4 13.8 Gonad Extending O 29.8 0 ,t.4 0 0 Not extending ! 00 70.2 100 95.6 100 100 Tail Terminus Smooth 65.4 58 68.2 65.4 40.8 67.7 Crenate 34.6 42 31.8 34.6 59.2 32.3

No differences were found in V value. 'Wando' pea plants in 10 randomized repli- Qualitative characters of P. penetrans cates of four nitrogen and light intensity on peas were influenced in a manner similar levels (low N: low light, low N: high light, to that observed in the preceding experi- high N: low light, and high N: high light) ment (Table 4). In 26.l% of females were inoculated with 500-1,000 P. penetrans. recovered from peas, the gonad extended The low-light-intensity treatments [3,870 anteriorly to the region of the esophageal lux (360 ft-c.)] were established by shading glands, but this was not observed in the re- with cloth, as opposed to high-light- maining treatments. A very high percentage intensity treatments maintained at 21,520 of nematodes recovered from peas also lux (2,000 ft-c.). Nitrogen levels were ob- showed an almost round median bulb as tained by fertilizing twice a week with compared with the normal oval median 0.02 M ammonium nitrate (high N treat- bulb occurring in most remaining treat- ments), whereas fertilizer was not added to ments. In all treatments, the percentage of the nitrogen-deficient soil used. The plants crenate tails remained about the same as were kept in a growth chamber at 21 C and that of the initial inoculum. The shape of a photoperiod of 12 h for 18 weeks. Nema- stylet knobs also varied among treatments. todes were extracted and 60 randomly Effects of nitrogen and light intensity.-- selected females from each treatment and 60

TABLE 3. Morphometric characters of Pratylenchus penetrans as influenced by feeding vs. storage with- out food.*

L Width Esophagus Stylet V a b' c Treatment (#m) (#m) (#m) (#m) (%) (Ratio) (Ratio) (Ratio)

Alfalfa callus 573.0 b 22.4 b 136.5 a 17.1 ab 79.6 a 25.8 b 4.2 b 18.4 b On peas 596.6 a 26.6 a 131,5 ab 16.8 b 80.0 a 22.5 c 4.6 a 19.9 a In soil 540.4 c 19.5 c 130.6 b 17.3 a 79.9 a 27.8 a 4.1 b 18.3 b In water 556.9 bc 21.9b 133.0 ab 17.3a 79.5a 25.7b 4.2b 18.4b Coefficient of variability (%) 7.64 9.65 8.05 4.91 1.85 9.48 9.48 11.97

•Treatment means with a letter in common do not differ, using Tukey's Honesty Significant Differences (e = 0.05). 190 Journal of Nematology, Volume 8, No. 3, July 1976 TABLE 4. Morphological characters of Praty. 29 C. Numerous nematodes were extracted lenchus penetrans females as influenced by feeding from roots of plants grown at 29 C, and 50 vs. storage without food. randomly selected females were studied and compared with 50 females from the initial % females inoculum. Alfalfa Differences were found in total length Character callus Peas Soil Water of the nematode, width, esophagus length, stylet length, and V value (Table 5). Nem- Stylet Knobs atodes from peas were longer and wider, Sloping 21.6 16.6 5.5 14.0 Rounded 21.6 42.6 41.8 36.0 had a shorter esophagus and styler, and the Fiat. or indented 56.8 40.8 52.7 50.0 vulva was located in a more posterior posi- Median Bulb tion in comparison with those of nematodes Oval 92.4 24.5 78.4 91.5 from the initial inoculum. The female Almost round 7.6 75.5 21.6 8.5 gonad extended anteriorly to the esophageal Gonad glands region in 17.6% of the nematodes Extending 0 26,1 0 0 from pea roots, but did not in any of the Not extending 100 73.9 100 100 nematodes from the inoculum (Table 5). Tail Terminus The percentage of females with crenate tails Smooth 66.0 68.3 73.9 73.6 was 51.1 from pea roots in comparison Crenate 34.0 31.7 26.1 26.4 with 32% of the females from the inoculum with crenate tails. The morphological re- from the initial inoculum were compared. sponse of the nematodes to feeding in pea No differences were found among the treat- roots in this experiment was for most char- ments in body length and width, esophagus acters identical to that of the preceding length, and b' ratio. However, there was a experiments. Only the V value changed. difference in the ratio a between nematodes Effects of culture media.--Nematodes from the initial inoculum and those from cultured in Krusberg's (K) medium (16) all treatments. Nematodes were longer and and modified White's (W) medium (24) wider, and had a shorter esophagus in these for 5 months were extracted, and 30 females treatments. Stylets were shorter in the high from each culture medium were studied and N: high-light-intensity treatment than in compared. Fewer nematodes and a higher the other treatments. ratio of males to females were obtained with The female gonad extended anteriorly W than with K medium. to the region of the esophageal glands in Tile bodies and stylets of females reared 20.3%, 15.4%, 21.1%, and 21.2% of the in K medium were longer than in those nematodes from the low N: low light, low reared in modified W medium. No differ- N: high light, high N: low light, and high ences were found in width, esophagus N: high-light treatments, respectively. This length, and V value. The female gonad did type of gonad was not observed in any of not extend anteriorly to the region of the the nematodes from the initial inoculum. esophageal glands in either treatment. The Compared to that of the inoculum, a higher percentage of females with crenate tails was percentage of females with an almost round higher in K medium (44.8%) than in W median bulb occurred in the treatments, medium (27.5 %). especially in the high-light treatments. The percentage of females with a crenate tail VARIATION IN POPULATIONS FROM DIFFER- was 44.1%, 48.2%, 55.1%, and 47.2% for ENT GEOGRAPHICAL LOCATIONS: Preserved ttle low N: low light, low N: high light, specimens from populations of P. penetrans high N: low light, and high N: high light from 14 geographical locations in Europe, treatments respectively, in comparison to Asia, North America, and the Caribbean 32% in the inoculum. were examined. In most, a variability sim- Comparison of P. penetrans from alfalfa ilar to the Cornel1 population was noted. callus and pea plants at 29 C.--A suspension The female-tail terminus was observed for of P. penetrans was added to each of 24 466 specimens (2-20/population) and 'Wando' pea seedlings. The plants were 33.3% 0-80%/population) had a crenate- kept for 6 months in a growth chamber at tail tip (Table 6). The same types of tail Variation in P. penetrans: Tarte, Mai 191

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crenation found in the Cornell University DISCUSSION population were found in most of tile geo- graphical populations studied (Fig. 3-A, B). Tile Cornell population and others from Morphological observations made for each different geographical locations exhibited population were recorded in Table 6. extensive morphological variation. Different 192 Journal of Nematology, Volume 8, No. 3, July 1976 TABLE 5. Comparison of morphometric qualitative morphological characters of Pratylenchus penetrans from alfalfa callus and pea plants at 29 C.'

L Width Esophagus Stylet Gonad Tail terminus Treatment (#m) (#m) (#m) (#m) V extending Smooth Crenate

Alfalfa callus 558 a 20 a 137 a 17.5 a 79.3 a 0 68 32 Peas 601 b 26 b 125 b 17.0 b 80.3 b 17.6 48.9 51.1 Coefficient of variability (%) 4.94 7.75 7.8 3.7 1.94 ------

*Treatment means with a letter in common do not differ, using Tukey's Honesty Significant Differences (P = 0.05).

environments induce variation in mor- to have striations around the tail tip. phometric and morphological characters. Dolliver (8) also mentioned that a few The validity of many characters used for specimens in a New York population of species determination is, therefore, ques- P. penetrans from orchard grass (Dactylis tioned. The value of many others will glomerata L.) had annulated-tail tips. Fe- undoubtedly depend on results of careful male nematodes with a crenate tail occurred studies o[ their variability. The shape of the in most populations that we studied. The stylet knobs is variable, and this variation proportion of individuals having this char- supports Roman and Hirschmann's (25) acter was changed by altering the environ- statement that it is a questionable character ment. Of the factors tested, host plant was for separating species of Pratylenchus. The most effective in inducing changes in this outer margin of the cephalic framework is qualitative character. The proportion of also variable in length, and in taxonomic crenate-tail females was higher in indi- studies, its extension posteriorly into the viduals from cabbage and peas than from body annulation should be utilized with the other hosts or initial inoculum from al- caution. Variation in the shape of sper- falfa callus. The only instance in which matheca and vulval lips should be carefully the percentage of crenate tails remained as determined. Both characters, as commonly low as in the initial inoculum was in the used in species differentiation, are not very short-term experiment testing the effect of reliable because of their variability. feeding on peas, in which nematodes re- The presence of a fifth lateral line in covered 3 weeks after inoculation were prob- specimens indicates that caution should be ably the same nematodes used as inoculum. used when consideration is given to the Nematodes cultured on K medium have a number of lateral lines. Roman and Hirsch- higher percentage of crenate tails as com- mann (25) indicated that 4, 5, 6, or 8 pared with those cultured in W medium. incisures in addition to other modifications The constant occurrence of 30 % females may occur in P. penetrans, and Sher and with crenate tails in callus-culture popula- Allen (28) mentioned that in the genus tions on W medium, regardless of age of Pratylenchus, sometimes 5 and 6 lines are the culture, and the increase of this per- seen in the region immediately anterior to centage when nematodes fed on pea roots the vulva. for several generations, suggest that peas In agreement with Roman and Hirsch- may modify the phenotypical expression of mann (25), no deviations from the normal, tail type not only as a direct influence of three-annule lip pattern were found in any such environment but quite possibly of the populations of P. penetrans studied. through a selective force. Selection, as Also, a change in number of lip annules pointed out by Mayr (21), is the most was not induced by altering the environ- important of the factors that induce evolu- ment. These data indicate that this is a re- tionary changes by affecting the frequency liable taxonomic character for P. penetrans. of genes in populations by a mechanism Taylor and Jenkins (30) stated that such as differential reproduction or differ- some specimens of P. penetrans appeared enti~l survival. He stated that the selective Variation in P. penetrans: Tarte, Mai 193

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{ ~ == ~ =/ a,) =.= 194 Journal of Nematology, Volume 8, No. 3, July 1976 response is extraordinarily sensitive to slight beyond the range limits given by Sher and environmental changes. Assuming that this Allen (28) and Loof (19). Pratylenchus sub- is a genetically controlled character, as our penetrans Taylor and Jenkins, 1957; P. unpublished data indicate, it is very likely fallax Seinhorst, 1968; P. pseudopratensis that peas are selective for crenate tails. The Seinhorst, 1968; P. convallariae Seinhorst, possibility exists that, because of the rela- 1959; P. wdnus Sher and Allen, 1953; P. tive adaptive capability of genotypes, some ondinus Lordello et al., 1961; and P. hosts will be even more selective than peas sudanensis Loof and Yassin, 1970 are very for females with crenate tails. The presence similar in morphology to P. penetrans (19, or absence of striations in the tail terminus 20, 25, 26, 27, 28, 29). should not be used as a main diagnostic The variability of P. penetrans originat- character for separating species in the genus ing from a single gravid female was so Pratylenchus. extensive that a certain percentage of the in- Host plant also influenced the length dividuals in any of the environments tested of the female gonad and the shape of the possessed all of tile characters of another median bulb. In 15.4% to 29.8% ot tile Pratylenchus species. Individuals possessing females feeding on pea roots, the gonad all characters of P. fallax Seinhorst, 1968; extended anteriorly into the region of the P. convallariae Seinhorst, 1959; and P. esophageal glands, whereas it did not ex- pseudopratensis Seinhorst, 1968 and most tend that far in females from callus culture. characters of P. sub-penetrans Taylor & An indication of a similar situation was re- Jenkins, 1957; P. wdnus Allen 8~ Jensen, ported by Loof (19) who observed that, in 1951; and P. sudanensis Loof & Yassin, 1970 a population of P. penetrans from , were observed. P. andinus Lordello, Zamith the ovary usually extended past the esopha- g: Boock, 1961 is reported to have no males geal glands and sometimes even past the and no spermatheca; yet under certain con- median bulb. Ovary length varied consider- ditions, a low percentage of males may be ably and it appears to be dependent on age present in P. penetrans, and because of the and nutritional status of tile individual (19, fixation technique, the spermatheca may ap- 25). In apparently older individuals, it ex- pear to be absent. No indication of the tends up to tile esoplmgeal glands. The use number of specimens examined is given in of this character in species diagnosis is not the description of P. andinus. According to advisable. Seinhorst (27), P. fallax differs from P. Nematodes from peas were longer and penetrans only in having a crenate-tail tip. wider, whereas their stylets and esophagi When specimens of P. fallax were studied, were shorter in comparison to those in almost no differences were found in the fe- nematodes from the alfalfa callus inoculum. male-tail tips when they were compared Esophageal length is independent of body with tile tail tips of similar P. penetrans length, and therefore, any ratio involving females (Fig. 3-C). these two characters is of no taxonomic It is highly probable that some of the value. The fact that ratio b' has no meaning previously mentioned species may be con- supports in part Geraert's (11) statement specific with P. penetrans. However, only a about the invalidity of its similar ratio b. detailed study of the variation present, and The V value, because it was not nor- possibly the performance of interbreeding mally changed by the environment to a tests with P. penetrans, will reveal their considerable extent and had the lowest coef- specific status. ficient of variability, is of good diagnostic LITERATURE CITED value. Stylet length, although having a low coefficient of variability, was shorter in nem- I. BARRACLOUGH, R., and R. E. BLACKITH. 1962. Morphometric relationships in the atodes from peas and other host plants than genus Ditylenchus. Nematologica 8:51-58. in those from alfalfa callus tissue. A 2. BIRD, A. F. 1967. Physiological and mor- morphometric character showing a low phological changes associated with parasitism coefficient of variability, however, can be under monoxenic conditions in Meloidogyne modified by the environment and, if so, it javanica. J. Parasitol. 53:768-776. 3. BIRD, G. W., and W. F. MAI. 1967. Factors in- should be carefully used in diagnosis. fluencing population densities of Trichodorus Some morphometric characters extended christiei. Phytopathology 57:1368-1371. Variation in P. penetrans: Tarte, Mai 195

4. COOMANS, A. 1962. Morphological observa- 18. LINFORD, M. B. 1937. The feeding of the root- tions on Rotylenchus goodeyi Loof and knot nematode in root tissue and nutrient Oostenbrink, 1958. I. Redescription and solution. Phytopathology 27:824-835. variability. Nematologica 7:203-215. 19. LOOF, P. A. A. 1960. Taxonomic studies on the S. COOMANS, A. 1963. Observations on the genus Pratylenchus (Nematoda). Tijdschr. variability of morphological structures in Plantenziekten 66:29-90. Hoplolaimus pararobustus. Nematologica 9: 20. LOOF, P. A. A., and A. M. YASSIN. 1970. Three 241-254. new plant-parasitic nematodes from the 6. COOMANS, A. 1971. Morphology and nematode Sudan, with notes on Xiphinema basiri Sid- systematics. J. Parasitol. 57:95-99. diqi, 1959. Nematologica 16:537-546. 7. CROFTON, H. D. 1971. Form, function and be- 21. MAYR, E. 1963. species and evolution. havior, pages 83-113 in B. M. Zuckerman, The Belknap Press of Harvard Univ. Press, W. F. Mai, and R. A. Rohde, eds. Plant Cambridge, Massachusetts. 797 p. parasitic nematodes. Vol. I., Academic Press, 22. McELROY, F. D., and S. D. VAN GUNDY. Inc., New York and London. 1968. Observations on the feeding processes 8. DOLLIVER, J. S. 1961. Population levels of of Hemicycliophora arenaria. Phytopathology Pratylenchus penetrans as influenced by treat- 58:1558-1565. ments affecting dry weight of Wando pea 23. MINTON, N. A., and A. M. GOLDEN. 1966. plants. Phytopathology 51:364-367. Morphological variations of Hemicycliophora 9. DROPKIN, V. H. 1953. Studies on the variabil- zuckermani Brzeski. Nematologica 12:179-180. ity of anal plate patterns in pure lines of 24. RIEDEL, R. M., and J. G. FOSTER. 1970. Meloidogyne spp. The root-knot nematode. Monoxenic culture of Ditylenchus dipsaci and Proc. Hehninthol. Soc. Wash. 20:32-39. Pratylenchus penetrans with modified Krus- 10. FISHER, J. M. 1965. Studies on Paratylenchus berg's and White's media. Plant Dis. Rep. 54: nanus. I. Effects of variation in environment 251-254. on several morphometric characters of adults. 25. ROMAN, J., and H. HIRSCHMANN. 1969. Nematologica 11:269-279. Morphology and morphometrics of six species 11. GERAERT, E. 1968. Morphometric relations in of Pratylenchus. J. Nematol. 1:363-386. nematodes. Nenmtologica 14:171-183. 26. SEINHORST, J. v~T. 1959. Two new species of 12. GOODEY, J. B. 1952. The influence of the host Pratylenchus. Nematologica 4:83-86. on the dimensions of the plant parasitic 27. SEINHORST, J. w. 1968. Three new Praty- nematode, Ditylenchus destructor. Ann. Appl. lenchus species with a discussiort of the Biol. 39:468-474. structure of the cephalic framework and of 13. GOODEY, J. B. 1959. Data to be considered, oh- the spermatheca in this genus. Nematologica. served arid, where possible, reported upon 14:497-510. when presenting descriptions of new species. 28. SHER, S. A., and M. W. ALLEN. 1953. Re- Nematologica 4:211-216. vision of the genus Pratylenchus (Nematoda: 14. GOODEY, T. 1941. Observations on a giant race Tylenchidae). Univ. California Publ. Zool. of the stem eelworm, Anguillulina dipsaci, at- 57:441-469. tacking broad bean Vicia faba L. J. Hel- 29. TARJAN, A. C. 1969. Variation within the minthol. 19:114-122. Xiphinema americanum group (Nematoda: 15. (;RISSE, A. De. anti P. A. A. LOOF. 1970. Intra- Longidoridae). Nematologica 15:241-252. specific variation in some 30. TAYLOR, D. P., and W. R. JENKINS. 1957. (Nematoda). Meded. Fac. Landbouwwet. Variation within the nematode genus Praty- Rijksuniv. Gent. 35:41-63. lenchus, with the descriptions of P. hexincisus, 16. KRUSBERG, L. R. 1961. Studies on the cultur- N. Sp. and P. subpenetrans N. Sp. Nema- ing and parasitism of plant parasitic nema- tologica 2:159-174. todes, in particular Ditylenchus dipsaci and 31. TRIANTAPHYLLOU, A. C., and J. N. SASSER. Aphelenchoides ritzemabosi on alfalfa tissues. 1960. Variation in perineal patterns and host Nematologica 6:181-200. specificity of Meloidogyne incognita. Phyto- 17. LAMBERTI, F. 1972. Morphological variations pathology 50:724-735. and geographic distribution of Longidorus africanus Merny. Nematropica 2:7 (Abstr.).