Seasonal Variation in Hatching of Eggs of Heterodera Avenae

Rate of hatching of new-season's eggs of H. avenae in South Australia changed only to a small extent over summer when soil temperatures were high (> 20°C), but in each of two years a sharp increase in the rate coincided with the onset of low soil temperatures in late autumn-winter. Low temperature was not essential for hatching but in the laboratory broke dormancy more rapidly. High soil moisture tensions (pF4) inhibited eclosion but permitted changes which enabled eggs to hatch. These changes were associated with the egg and not the cyst wall. A type of dormancy which suppressed hatch was induced in a proportion of encysted eggs when they were moved to 20° following 8 weeks at 7°. Eggs entered a similar type of dormancy in the field in spring. There was no evidence of an inherent seasonal cycle of hatching. The significance of these changes in relation to activity and survival of the nematode and damage to cereal crops under local conditions is discussed.