Ascospore deposition in Eutypa armeniacae

Abstract

An open-circuit wind-tunnel designed for spore deposition studies at wind speeds up to 9 m/sec is described. Deposition of Eutypa ascospore octads on three components of the host surface was investigated at four wind speeds. The efficiency of deposition on petioles exceeded that on leaves or stems; and for all surfaces, the deposit increased with wind speed within the range 1–5 m/sec. Deposited ascospores were readily removed from leaves by brief contact with water, and must therefore be regarded as available for redispersal in rain wash and rain splash. The deposit of ascospores on defoliated shoots was only 3.5% of that on the corresponding foliated structures; thus the risk of ascospores reaching the infection courts is markedly diminished by leaf fall. In an apricot orchard, winds of less than 2 m/sec predominated close to the tree foliage at 2 m above ground level. Comparative studies with rigid artificial surfaces of gross dimensions similar to those of apricot petioles suggested that the efficiency of deposition of E. armeniacae octads on such narrow surfaces may be influenced by the shape and mobility of the target surface.