Overwintering of Venturia inaequalis, the causal agent of apple scab, on different cultivars

A maturation index summarising pseudothecial development of Venturia inaequalis was devised. The index demonstrated differences in overwintering on 10 apple cultivars and the crab apple Malus toringo in experiments over two winters. At about the green cluster stage, when there is a high proportion of susceptible foliage, there were 50–100 fold differences in the yield of ascospores from these hosts, due mainly to different rates of pseudothecial maturation. These rates were shown to be independent of cultivar differences in colony numbers on leaves in the previous autumn.
Cultivar differences in the timing of fruit bud development were independent of differences in the overwintering of V. inaequalis . These findings confirm the importance of considering cultivar identity in apple scab management.