Pratylenchus

Pratylenchus Filipjev, 1934

Suborder Tylenchina: Family Pratylenchidae (ref. ID; 3547)

Family Pratylenchidae (ref. ID; 5954, 6168, 6182)

ref. ID; 1923

Female with 1 ovary; males with caudal alae surrounding tail tip. (A large genus, about 20 named species, primarily terrestrial) (ref. ID; 1923)

ref. ID; 6691, 6859

Plant parasite. (ref. ID; 6691, 6859)

Pratylenchus brachyurus (ref. ID; 3547)
Pratylenchus coffeae (Zimmerman, 1898) (ref. ID; 7621)
Pratylenchus crenatus Loof, 1960 (ref. ID; 5954) reported author and year? (ref. ID; 7621)
Pratylenchus fallax Seinhorst, 1968 (ref. ID; 5954)
Pratylenchus mulchandi Nandakumar & Khera (ref. ID; 7621) reported author and year? (ref. ID; 1751)
Pratylenchus neglectus (Rensch, 1924) Filipjev & Schuurmans Stekhoven, 1941 (ref. ID; 5954)
Pratylenchus penetrans (Cobb, 1917) Filipjev & Schuurmans Stekhoven, 1941 (ref. ID; 5954)
Pratylenchus pratensis (de Man, 1880) (ref. ID; 2588) reported author and year? (ref. ID; 7621)
Pratylenchus scribneri (ref. ID; 3547)
Pratylenchus zeae (ref. ID; 7621)

Pratylenchus mulchandi Nandakumar & Khera (ref. ID; 7621) reported author and year? (ref. ID; 1751)

Descriptions

The eggs of Pratylenchus mulchandi are laid singly. Only a single fully formed egg is held in the uterus at a time and egg laying could be observed under the microscope. The egg shell, being plastic and pliable, is squeezed out of the transverse slit - like opening of the vulva. The nematode swings its hind end from side to side several times to expedite the extrusion of the egg. An exudate is discharged along with the extrusion of the egg. Owing to the extreme nomadic habit of the nematode, the total number of eggs laid by a single female could not be observed. In the early stages of development the eggs are generally round in shape, but as development proceeds may become reniform. The average dimensions of 58 eggs in different stages of embryonic development were 72(60-90)x25(20-35) µm. The egg shell is thin and transparent with a smooth surfae, and almost in close contact beneath it, is the thin vitelline membrane. The latter was visible only when it had receded from the egg shell or when the egg protoplasm (made up to closely packed globules of uniform size) had shrunk away from the walls. The shrinkage left an extra-vitellar cavity between the vitelline membrane and the egg shell near the poles. Only a single, extra-vitellar polar body could be observed. Newly deposited eggs vary from the unicellular to the multicellular stage. It is not uncommon to find cleaved eggs in the various stages of development up to first larval stage inside the body of the mother. Vigorous streaming movement of the contents of this larva was observed inside the uterus of a number of female specimens. This phenomenon of eggs undergoing cleavage before release from the uterus was observed not only in specimens from the stock cultures, but also in those collected from the field. (ref. ID; 7621)

Hatching. The coiled, first stage larva occupied almost the entire space within the egg shell, its head and tail regions being folded over or below one another or being quite apart. Prior to hatching the larva moved actively within the egg rotating its head in various directions during which the lip region was found to press against the egg shell, often causing bulging in the latter. The stylet was not observed to thrust against the egg shell. No hatching was observed in the eggs placed in water. (ref. ID; 7621)
Moulting in the free living stages. The process of moulting is essentially the same in all the free living stages. Larvae became quiescent prior to a moult with occasional jerky movements. The protoplasm then receded away from the cuticle; the anterior part of the stylet and cephalic framework remained in contact with the moulted cuticle. The posterior part of the stylet was very faintly visible. Specimens had been observed with noticeably loose cuticle either in the anterior region or in the posterior region only or in both the regions forming a loose cover over the entire body. The cuticular linings of the excretory pore, hemizonid and rectum were also shed and the linings of these structures were found in the cast off cuticle. Striations of the old body cuticle became fianter acquiring a stretched appearance causing the cuticle to slacken around the newly moulted larva thereby forming a loose cover over the latter. The new conoid part of the stylet as well as the shaft and basal knobs and the lining of the excretory pore and hemizoid were reformed. Exsheathment could not be observed. (ref. ID; 7621)
Larval stages. It was extremely difficult to categorize different developmental stages of Pratylenchus mulchandi because of the overlapping ranges in the absolute measurements and the de Manian formula. Various stages were, therefore, distinguished by anatomy and gonadial development. (ref. ID; 7621)
Post-embryonic development. The first moult occurs within the egg and the second stage larva hatches out. Genital primordium cylindrical with rounded ends, of four cells - two large, rounded, centrally located germinal cells arranged tandemwise each with a conspicuous nucleus, bordered anteriorly and posteriorly by two smaller somatic cells. In newly hatched specimens the two germinal cells closely adhere to each other. (ref. ID; 7621)
Second moult (n=11). Cephalic framework 2-2.5 µm. Germinal cells have started moving away from each other leaving a gap between them. This gap is ultimately filled by cells resulting from the rapid division of the somatic cells. (ref. ID; 7621)
Third stage larva (n=32). The two germinal cells of the germinal primordium are now separated by a distance of 6-22 µm. The gap has been filld by cells from the multiplication of the somatic cells. The gap between the germinal cells increases with the increase in the number of derivatives of the somatic cells, and the primordium enlarged. Usually at this stage the genital primordium becomes spindle shaped. (ref. ID; 7621)
Third moult (n=15). Rapid changes take place in the genital primordium during this stage. It becomes more elongate and the two germinal cells of the genital primordium are pushed towards opposite ends of the gonad by the formation of additional somatic cells between them. The gonad is uniformly wide except a little behind its middle where it has become somewhat swollen due to rapid division of somatic cells; this thickening marks the future uterus region. Up to this stage there is no indication of the future vagina. (ref. ID; 7621)
Fourth stage larva (n=15). At this stage the larvae begin to resemble the adults. The two germinal cells of the genital primordium begin to divide and a single row of oocytes can be seen at the opposite ends of the gonad. There is further aggregation of cells in the swollen sacciform uterine region of the gonad with a depression towards the ventral side; the uterine region starts getting differentiated a little later. The entire gonad is elongated and continuous, extending from the middle of the body to near the anus. The vaginal primordium of the late fourth stage larva is marked by a slight differentiation of the cell masses in the ventral chord opposite the uterine depression in the form of hyaline sac which appears incompletely connected to the gonad at one end and to the body wall on the other. (ref. ID; 7621)
Fourth moult (n=10). With the appearance of the lumen of vagina the post-uterine sac is distinguishable from the rest of the gonad, the regions of the uterus and ovary become clearly differentiated; the ovary increases in size. The vagina and vulva complete their development and connexion between the gonad and the outside is established. By the end of the fourth moult the various parts of the anterior female gonad are distinguishable. The post-uterine sac comprises the usual uterine extension along with a rudimentary ovary of 2-3 cells. (ref. ID; 7621)
Adult. The nematodes emerge as young adults after the fourth moult with fully developed gonad. In the adults the ovary continues to increase in size and in some females, the ovary reaches the level of the oesophago-intestinal junction. There is a considerable variation in the morphology of the ovary in P. mulchandi. The ovary is usually outstreched in Pratylenchus species, but in P. mulchandi, the ovary is occasionally reflexed (Nandakumar and Khera 1969). Considerable variation has also been observed in the arrangement of oocytes, which are either in a single row or in a double row, beginning slightly posterior to the cap cell. Sperm was not found in any of the specimens examined. (ref. ID; 7621)

Length of the life cycle. Due to the extreme vagrant habits of the nematode, the exact morphological sequence of the various larval stages could not be followed. The life cycle is completed within 24-36 days in petri plates containing pearl millet seedlings at room temperature - 6 to 10 days for the eggs to hatch, 15 to 20 days for the second stage larvae to mature into adults, and 3 to 6 days from maturation to egg laying. (ref. ID; 7621)

Habitat

Plant parasitic nematodes around the rhizosphere of pearl millet, Pennisetum typhoides, the nematode was subsequently cultured on callus tissue (Nandakumar and Khera 1969). (ref. ID; 7621)