HATCHING IN THE POTATO CYST NEMATODE GLOBODERA ROSTOCHIENSIS INDICATING DIAPAUSE AS A CAUSE OF VARIABILITY IN EMERGENCE

Z. Muhammad, A. A. F. Evans

Abstract


Over a period of 12 months "new" cysts (extracted soon after maturity on host roots) and "old" cysts of Globodera rostochiensis (stored for one calendar year outdoors in a gravel plunge) were hatched in potato root diffusate. Diapause was evident in "new" cysts in early autumn, winter, spring and mid-summer but was absent in late autumn and summer. By contrast when "old" cysts were hatched, emergence was about 90% in all periods. It is suggested that diapause persists in "new" cysts, but is overcome when cysts are stored for 12 months in the soil outdoors. A comparison of infectivity of juveniles obtained in the periods when eggs have overcome their diapause failed to show any differences. Also when the number of eggs in "new" and "old" cysts were compared, the number of eggs in "old" cysts exceeded the number of eggs in "new" cysts. It is suggested that hatching in "old" cysts is due to absence of diapause. The presence of large numbers of eggs in "old" cysts even after 12 months storage outdoors in the soil failed to support the theories of hatching, microorganism induced hatching or persistence of hatching factors in the soil.

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