The quantity of inoculum required to infect apricot and other prunus species with Eutypa armeniacae

Abstract

In the field, infection of apricot occurred when inocula of 10 or 100 ascospores of E. armeniacae were applied to wounds on the day of pruning. The proportion of wounds infected was doubled when the inoculum dose was increased from 10 to 100 ascospores. On sheltered trees, by contrast, freshly-made wounds were equally susceptible (c. 90 per cent) to infection from doses of 10 and 100 ascospores. When no rain fell for 12 days after pruning, large inocula (100, 1000 ascospores) applied on day 15 caused infection of a high pro- portion of wounds on unsheltered apricot trees. Infection of almond, peach, and prune was also induced by inoculation. Although there was extensive xylem invasion in these hosts, the fungus did not produce the symptoms of cankering and lateral collapse seen in apricot. Our results suggest that the number of ascospores naturally deposited on individual pruning wounds is normally less than 10, and that inocula of this size therefore are more appropriate than the larger doses used previously.