Pathogenic behaviour of strains of Albugo candida from Brassica juncea (Indian mustard) and Raphanus raphanistrum (wild radish) in Western Australia

White rust caused by Albugo candida is a serious pathogen of Brassica juncea (Indian mustard) and one posing a potential hazard to the presently developing canola-quality B. juncea industry in Australia. The varieties of B. juncea available in Australia are known to be susceptible to attack by race 2 of A. candida, a race that is known to have two pathotypes, 2A and 2V. Two isolates of A. candida, representing strains collected from B. juncea and Raphanus raphanistrum (wild radish) from two sites in Western Australia (WA) were tested on cruciferous host differentials to characterise their pathogenic behaviour. The results clearly show that the strains obtained from B. juncea and R. raphanistrum are different in their host range. The isolate from B. juncea showed significant levels of sporulation on both differential cultivars of B. juncea, Vulcan and Commercial Brown, used for differentiating pathotype 2A from 2V, confirming the presence of pathotype 2V in WA. This is the first report of pathotype 2V in Australia. This same isolate was able to infect Brassica napus from China (FAN 189), B. tournefortii (wild turnip) B. nigra and R. sativus. This serves as a caution to breeders when sourcing resistance against A. candida from B. napus germplasm. The isolate from R. raphanistrum, tested against the same set of cruciferous host differentials, caused significant sporulation on B. juncea differential Commercial Brown, B. napus (FAN 189), B. nigra (90745), R. raphanistrum and R. sativus (White Icicle). Our strain from R. raphanistrum, while being a direct threat to B. juncea, may be a hazard, not only to any B. napus germplasm developed from B. napus breeding lines from China, but also to B. nigra and R. sativus, should these species be utilised commercially in Australia. The race delineations of these strains from the WA grainbelt are expected to be helpful for selecting appropriate genotype resistance(s) for sowing in relation to the planned expansion of the B. juncea industry and also if there is future development of alternative cruciferous oilseed industries in WA.