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Embryology and Life Cycle of Tylenchorhynchus Claytoni Steiner, 1937 (Nematoda: Tylenchoidea) 1

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Embryology and Life Cycle of Tylenchorhynchus Claytoni Steiner, 1937 (Nematoda: Tylenchoidea) 1 Embryology and Life Cycle of Tylenchorhynchus claytoni Steiner, 1937 (Nematoda: Tylenchoidea) 1 L. H. WANG2 Abstract: Development of Tylenchorhynchus claytoni from unsegmented egg to hatching takes 135 hr at 22-25 C. The fourth molt lasts 5 to 6 days. During exsheathment the cast cuticle of the larva separated into two unequal parts, breaking near either the anterior or posterior end. The life cycle from egg to egg required from 31 to 38 days at 28 C on alfalfa seedlings and included four molts and four larval stages. Sexual differentiation was apparent in third-stage larvae. Key Words: Egg-laying, Embryogenesis, Molting, Postembryogenesis. The tobacco stunt nematode, Tylenchor- ond-stage larvae. The soil in containers, hynchus claytoni Steiner, is considered to be replicated four times, was examined at 1-3 pathogenic to some agricultural and nursery day intervals for larval development. Mea- crops (13, 14, 19, 21). In 1959 Krusberg surements were made on heat-relaxed speci- (14) investigated its life cycle, reproduction, mens mounted in 2% cold formalin. Gonad feeding habits, and host ranges. The studies development was studied in nematodes reported here deal with its embryology, stained with 5% acid fuchsin (22). molting, and postembryonic development which have not previously been studied. RESULTS EGG-LAYING: Eggs were ]aid unseg- MATERIALS AND METHODS mented. Movement of the eggs in the uterus Nematodes were maintained on green- required 2-3 hr to travel one egg length. house-grown tobacco (Nicotiana glutinosa When the egg reached the vagina the nema- L.) at 22-28 C. Hand-picked gravid females tode began to swing its tail back and forth were transferred to BPI dishes containing and this, coupled with rolling of its body, tap water for observation of egg laying. Egg continued until the vulva opened. Prior to development was observed in a hanging drop egg deposition, movement of the female culture (18). Nematodes in fourth stage stopped, and the body became "W" shaped. molt were selected and transferred to water Eventually, the egg was squeezed out of the agar ( 11 ) for observation of molting. The vulva. The actual emergence of the egg study of postembryonic development was required 5-10 seconds. After the egg was deposited the female coiled and uncoiled conducted in a 13 × 90-ram soil-filled-con- several times and then resumed its normal tainer containing a 3-week-old alfalfa seed- undulating movement. ling inoculated with 100 newly-hatched sec- EMBRYOLOGY: Eggs were 62-68 ~ in Received for publication 24 December 1969. length by 20-23 ~ in width (n = 40). A vitelline membrane was first seen beneath i Portions of an M.Sc. thesis submitted to the Graduate Division, University of California, Riverside. the shell early in cleavage. The protoplasm o Department of Nematology, University of California, Riverside, California 92501. Present address: Depart- of the egg was granular with an irregular ment of Botany and Plant Pathology, Purdue University, Lafayette, Indiana 47907. The author is extremely grate- margin which became smooth prior to the ful to Drs. S. A. Sher and R. Mankau, Department of first cleavage (Fig. 1, A, B). The develop- Nematology, University of California, Riverside, and Dr. G. B. Bergeson, Department of Botany and Plant mental pattern, given in detail in Table 1, Pathology, Purdue University for valuable suggestions and criticisms. was based on 75 eggs. 101 102 Journal of Nematology, Vol. 3, No. 2, April 1971 TABLE 1. Chronology of embryogenesis from egg deposition to egg hatch. The labelling of blas- tomere embryogenesis was according to the system of Boveri (3). Hr since egg deposition Developmental sequence 3-4 First division at right angles to the longitudinal axis of the egg pro- duced cells $1 and P1 (Fig. 1, C). S, blastomere (regarded the an- terior cell) divided equally into an anterior "A" and a central "B" cell (Fig. 1, D). 10 "A" cell divided obliquely into an @ a-cell and an "a" cell (Fig. 1, E). 10.5 P~ cell divided into S.~ and P~ cells (Fig. 1, F). FIG. 1. Camera lucida drawings of egg cleav- 14 Cells shifted position resulting in age in T. claytoni. A. Unsegmented egg after "B" and S~ cells becoming triangular laying; B. Egg prior to the first cleavage; C-F. in outline (Fig. 1, G). Two to five-celled stage; (;. Shifting blastomeres 16 "B" cell divided into a /~ and a at five-celled stage; H-J. Six to eight-celled stage. "b" cell (Fig. 1, H). 17.5 S~ cell divided into an E and a MST cell (Fig. 1, I). MOLTIr~6: Prior to the final molt, larvae 19-20 P2 cell divided into a Sa and a Ps cell resulting in 8-celled stage egg were sluggish or inactive. The stylet ap- (Fig. 1, J). Polar body between peared less refractive, and the esophagus be- vitelline membrane and egg shell ob- served. came very faint. The stylet knobs disap- 20-3o Simultaneous cleavage throughout peared first and then the shaft. The apex the egg. remained intact and was later shed with the 30-35 Formation of blastula. vestibular extension and cephalic framework. 35-45 Formation of gastrula. Ceils began A flask-shaped hyaline cavity appeared differentiating into ectoderm and en- doderm. which surrounded the apex. Soon the head 45-68 Hyaline region formed at anterior started to pull back from the cephalic frame- end of egg which gave rise to the work. A short sclerotized tube developed 68 mouth, head, and esophageal region. Embryo moved and rotated within behind the hyaline cavity indicating the ini- egg. tiation of a new apex. As the head pulled 70 Formation of a tadpole-shaped farther back, the hyaline cavity diminished larva. 74 Larva became vermiform. and the new apex was completed. This was 74-95 Larva rapidly elongated and in- followed by the formation of the shaft and creased its activity. then the knobs. Later the knobs gradually 95-125 First molt occurred within the egg. A styler was first seen during the increased in size. The lumen of the esophagus molt. and the valve plate of the medium bulb be- 125-135 Larva moved frequently and vigor- came distinct. Development from the time ously, alternating with several im- mobile periods lasting 0.5-2 hr. Egg the knobs disappeared to the completion of shell appeared to become more flex- the stylet required 56-72 hr. After the ible. The styler repeatedly punctured stylet was completed the nematode resumed the anterior end of the egg. Egg shell ruptured and larva emerged within its activity. The old cuticle appeared pliable seconds. The rounded polar body and loose around the body. An unknown remained within the empty egg shell. LIFE CYCLE OF Tylenchorhynchus claytoni • Wang 103 FIG. 2. Exsheathment in T. claytoni. A. Anterior part of cuticle (Ant Cut.) split; B. Posterior part of cuticle (Post Cut.) split; C. Prior to exsheathment unknown material (Ukn Mat.) accumulated on the old cuticle. (Bas Blb ----- Basal Bulb; End Ant Cut. ---- End of anterior part of cuticle). material gradually accumulated between the ments of the different larval stages were old and the new cuticle near the end of either presented in Table 2. the esophagus (Fig. 2, C) or the anal area. Second-stage larva.--Genital primordium Later the old cuticle split at one of these measured 8-10 t~ long and was located at two areas (Fig. 2, A, B), and at exsheath- the right of the ventral chord at 58-62% ment the shorter part of the old cuticle, of body length. It consisted of four cells, two either the head or the tail portion, was ex- large germinal cells between two small cap sheathed first followed by the rest of the cells (Fig. 3, A). During the molt the genital cuticle. The break between cuticle segments primordium enlarged and measured 12-14 was usually a smooth circular split, but oc- in length. casionally it was jagged. The fourth molt Third-stage /emale larva.--The female lasted 5-6 days. gonad differed markedly from the male DEVELOPMENTAL STAGES: Three larval gonad at this stage. Two germinal cells of stages occur between hatching and the adult the genital primordium were separated by stage. Characteristics important for dis- two to four somatic cells, one germ cell tinguishing the various larval stages were: entering each end of gonad (Fig. 3, B). The structure and length of gonad, body length, gonad measured 20-26 t~ long. During the tail length, and tail width. The measure- molt the gonad extended in length and 104 Journal of Nematology, Vol. 3, No. 2, April 1971 TABLE 2. Dimensions of Postembryonic Stages of T. claytoni. Tail Tail Stage Length Width Stylet length width Second -stage 212-214t 12-15 15-17 23-29 10-- 12 (228.0) (13.5) (16.2) (26.0) (11.2) Third-stage 9 382-432 16--20 18-21 30-37 12-15 (400.6) (18.0) (19.0) (32.3) (13.9) Third-stage c~ 330-402 15-19 17-19 23-33 10-- 14 (358.4) (16.9) (18.2) (29.5) (12.5) Fourth-stage 9 504-598 22-24 19-21 32-40 14-16 (553.3) (23.0) (20.1) (36.2) (15.3) Fourth-stage ~ 435-523 20-23 18-20 33-38 16-20 (501.0) (22.2) (19.0) (37.3 ) (18.4) Female 638-720 24-28 21-23 35-40 15-19 (689.5) (26.6) (22.3) (37.7) (17.6) Male 595-695 21-25 20-22 42-51 15-17 (648.1) (23.4) (21.4) (44.1) (16.5) "t Measurements in g (n -~ 20).
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