First report of powdery mildew caused by Erysiphe cruciferarum on Brassica juncea in Australia.
In the spring of 2007, at the University of Western Australia field plots at Crawley (Western Australia, Australia), plants of B. juncea genotypes from Australia and China had extensive stem colonization by powdery mildew at the end of the flowering period, with whitish patches ranging in size from 3 mm to 3 cm long. Theses patches coalesced to form a densed, white, powdery layer as they expanded. Pathogenicity was demonstrated by gently pressing infected stems containing abundant sporulation onto leaves of potted B. juncea seedlings of cultivar JM-18, incubating the plants in a moist chamber for 48 h, and then maintaining the plants in a controlled-environment room at 18/13°C for day/night. When symptomatic plants were examined, abundant conidia were typical of Erysiphe cruciferarum, with cylindrical conidia borne singly or in short chains as described previously. This is thought to be the first record of E. cruciferarum on B. juncea in Australia.