Spore germination and disease development after application of pycnidiospores ofAscochyta caulina toChenopodium album plants

Abstract

Ascochyta caulina is considered a potential mycoherbicide againstChenopodium album. Disease development ofC. album plants and plants of 14 other species after application of pycnidiospores ofA. caulina was studied in climate chamber experiments. The experiments were carried out to analyse disease development with time, and to recognize factors that may limit disease development. Two time courses of necrosis ofC. album plants were observed, (1) an increase of necrosis followed by a decline, and (2) an increase of necrosis up to completion with subsequent plant death. Courses of necrosis with time could be described by a non-monotonic, critically damped model when plants survived infection and by a monomolecular model when plants died from infection. Disease development was influenced by interactions between wetness period, density of the spore suspension applied, plant development stage at the time of spore application, and temperature. Disease was favoured by a long wetness period, a high number of spores applied, an early plant development stage at the time of spore application, and temperatures of 18 ‡C and higher. Disease development was limited to plant species of the generaChenopodium, Atriplex andSpinacia with differences between the species. Pathogenicity differed significantly between threeA. caulina isolates tested. Variation in resistance between four source populations ofC. album was small. Prospects forA. caulina as a mycoherbicide are discussed.