Spore germination and disease development after application of pycnidiospores of Ascochyta caulina to Chenopodium album plants

Ascochyta caulina is considered a potential mycoherbicide against Chenopodium album. Disease development of C. album plants and plants of 14 other species after application of pycnidiospores of A. 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 of C. 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 degrees C and higher. Disease development was limited to plant species of the genera Chenopodium, Atriplex and Spinacia with differences between the species. Pathogenicity differed significantly between three A. caulina isolates tested. Variation in resistance between four source populations of C. album was small. Prospects for A. caulina as a mycoherbicide are discussed.