Agronomic challenges from novel pathotypes of Albugo candida to the emerging Brassica juncea industry in Western Australia

Abstract

It can be difficult to predict the outcome when a newly introduced crop is challenged by a specialized obligate phytopathogen. This case study explores the potential of Albugo candida, which causes white blister (WB) of Brassicas, to evolve into a major challenge to the broad acre crop Brassica juncea in the Western Australian (W.A.) ag- ricultural landscape. Brassica juncea is currently emerging as a viable replacement oilseed crop to B. napus, especially in parts of W.A. with diminishing rainfall. WB is known to be a greater threat to B. juncea than to B. napus. Studies to date indicate significant genetic diversity of A. candida populations in this region, with many pathotypes evolv- ing on exotic and native weed flora, and these may result in the development of strains that pose increased threats to B. juncea crops than those already encountered. Information gathered on pathogenic behaviour and defense mechanisms will assist understanding the nature of the appearance of novel pathotypes, and enable development of strategies to enhance host resistance to A. candida in B. juncea. Strategies to manipulate agronomic practices, such as weed control, may also help to reduce the hazards posed by newly evolving pathotypes in this region.