Diapause in the nematodeGlobodera pallida

Abstract

Over a period of 12 months 'new' and 'old' cysts of Globodera pallida were hatched in potato root diffusate according to a novel 'nematode-response' hatching protocol. In this protocol, cysts were set to hatch at the beginning of autumn and then left to indicate when their hatching ability was exhausted (when less than 100 juveniles/replicate/week emerged) before another batch of cysts was set to hatch. At any time of the year for the 12 months this experiment was conducted there were cysts hatching. After 12 months of hatching, eight hatching curves were obtained. Based on the hatching curves of the 'new' and 'old' cysts, diapause was shown to be present in 'new' cysts in autumn, winter and early spring. However, diapause was absent in late spring and summer.Infectivity assays to distinguish between juveniles obtained in the periods when cysts were in diapause and when cysts had overcome their diapause failed to show any significant difference in their infectivity. There was no significant difference in the number of eggs in 'new' and 'old' cysts. Based on this observation, it was suggested that high emergence in 'old' cysts may not be a result of few eggs in the cyst but rather due to absence of diapause. Also the presence of large numbers of eggs in "old' cysts even after being stored for 12 months outdoors in the soil does not support the theories of spontaneous hatching, micro-organism induced hatching or persistence of hatching factors in the soil.

Variation in in vitro hatch of potato cyst nematodes in response to different potato cultivars inoculated with isolates of arbuscular mycorrhizal fungi

“…Time constraints meant that it was not possible to repeat the trials presented here the following season. Considering published reports of seasonal variation in the hatchability of PCN J2 due to diapause (Fenwick & Reid, 1953;Muhammad, 1994;Jones et al, 1998) and to strengthen the confidence in the current findings, it is important that such hatching tests are repeated in time in future research of this nature.…”

The Cyst Nematodes

“…In G. rostochiensis, a greater number of juveniles emerge from cysts stored wet at 15 oc than thase stored dry at 10-15 oc (Muhammad, 1994), while emergence from cysts stored at 23 oc is 20-30 times greater than from those stored at 15 oc (Dunn, 1954). However, in some populations of G.…”

“…Many chemieals inhibit juvenile emergence ( Kaushal and Seshadri, 1986aSethi and Prasad, 1982JayaprakashandRao, 1981Garabedian and Hague, 1984Steele, 1977Steele and Hodges, 1975Steele, 1983Hangsteheck and Gleissl, 1988Perry and Beane, 1989aWong et al, 1993Takasugi et al, 1975Okada, 1972Takasugi et al, 1975Osbome, 1973Gonzalez et al, 1994Perry and Beane, 1988Perry and Beane, 1989bJones and Gander, 1962 PCN populationsundergo a phase of dormancy (Reinmuth, 1929;Hominick, 1986;Muhammad, 1994). The lip region exerts pressure on the egg shell and the stylet probes it.…”

“…The juvenile hatches out through the slit. Cysts produced under increasing daylength conditions have juveniles that emerge without any apparent inhibition whereas cysts obtained from plants grown under short-day conditions have juveniles that emerge at a low rate; increasing daylength conditions during reproduction prevents establishment of diapause (Salazar and Ritter, 1993 (Muhammad, 1994). Sometimes the juvenile becomes quiescent .…”

“…rostochiensis outdoors for a period of 12 months overcomes diapause but some eggs of G. pallida still exhibit diapause (Hominick, Forrest and Evans, 1985;Muhammad, 1990;Muhammad, 1994) 8…”