Distribution and Survival of Ascochyta Blight Pathogens in Field-Pea-Cropping Soils of Australia

Phoma koolunga, Didymella pinodes, and P. medicaginis var. pinodella were detected in DNA extracted from soil following field pea crops across four states in the southeastern and western regions of Australia. P koolunga was commonly detected in soil from South Australia but rarely in other states whereas D. pinodes plus P medicaginis var. pinodella were widespread in all regions tested. The quantity of DNA of these pathogens detected in soils prior to growing field pea was positively correlated with ascochyta blight lesions on field pea subsequently grown in infested soil in a pot bioassay and also on field pea in naturally infected field trials. The quantity of DNA of the soilborne pathogens was greatest following a field pea crop and gradually decreased in the following 3 years. The DNA tests were used to quantify the DNA of the pathogens in field pea plants sampled from naturally infected field trials in South Australia over two seasons. The combined results of DNA tests and pathogen isolation from the plants indicated that P koolunga and D. pinodes were equally responsible for the ascochyta blight symptoms in the diseased trials, while P medicaginis var. pinodella had a minor role in the disease complex.