Host Range and Phylogenetic Relationships ofAlbugo candidafrom Cruciferous Hosts in Western Australia, with Special Reference toBrassica juncea

Abstract

Kaur, P., Sivasithamparam, K., and Barbetti, M. J. 2011. Host range and phylogenetic relationships of Albugo candida from cruciferous hosts in Western Australia, with special reference to Brassica júncea. Plant Dis. 95:712-718.White rust, caused by Albugo candida, is a serious pathogen of Brassica júncea (Indian mustard) worldwide and poses a potential hazard to the presently developing canola-quality B. júncea industry in Australia. Nine isolates of A. candida, representing strains collected from B. júncea, B. rapa, B. olerácea, B. toumefortii, Raphanus raphanistrum, R. sativa, Eruca vesicaria subsp. sativa, Capsella bursa-pastoris and Sisymbrium irio, from different locations in Western Australia (W.A.), were tested on cruciferous host differentials to characterize their pathogenicity. In particular, these studies were aimed to determine the hazard to the newly emerging B. júncea industry in Australia from races or pathotypes of A. candida present. Pathogenicity tests with appropriate differentials demonstrated the presence in W.A. of a unique strain from iS. rapa that did not show characteristics of either race 7A or 7V and clearly is a distinct new pathogenic strain within race 7. Different strains collected from W.A. differed in their host range, with the strains from B. toumefortii and S. irio being highly host specific, failing to be pathogenic on any other differentials. B. toumefortii was host to a strain attacking B. júncea and E. vesicaria subsp. sativa. The strain from R. raphanistrum showed a relatively wide host range among the differentials tested. B. toumefortii, C. bursa-pastoris, R. raphanistrum, and 5. irio are common weeds within grain belt and horticultural regions in Australia. The B. olerácea isolate (race 9) was pathogenic to B. júncea 'Vulcan' whereas the isolate from B. júncea (race 2V) was not pathogenic on B. olerácea. Similarly, the strain from C. bursa pastoris (race 4) was pathogenic on B. júncea Vulcan but the B. júncea strain was not pathogenic on C. bursa pastoris. In contrast, the strain from R. sativus (race 1 ) was pathogenic on B. júncea and the B. júncea strain was also pathogenic on R. sativus. Field isolates from B. rapa, B. toumefortii, E. vesicaria subsp. sativa, and 5. irio were all nonpathogenic on B. júncea. Isolates from B. júncea and R. raphanistrum were pathogenic on B. napus (FAN 189). For the nine A. candida isolates from W.A., complete rDNA intemal transcribed spacer region nucleotide sequence analysis showed a nucleotide identity range of 72.4 to 100% in comparison with previous Australian collections of A. candida and those previously reported in Europe and Asia. The B. toumefortii isolate of A. candida from W.A. formed a distinct clade on its own, with an identity range of 77.4 to 80.5% compared with the other isolates. Isolates from R. raphanistrum and R. sativus from W.A. were least similar to the other isolates, with a nucleotide identity similarity of only 72.4%. Characterization of the races of A. candida in Western Australia adds to the current knowledg...

Phenotypic and phylogenetic studies associated with the crucifer white leaf spot pathogen, Pseudocercosporella capsellae, in Western Australia

“…This was to be expected, as close genetic relationships often exist amongst isolates from the same host, as found for several studies with other pathogens (e.g. Borromeo et al ., ; Browning et al ., ; Hsiang & Goodwin, ; Kaur et al ., ). Similarly, for the common bean anthracnose pathogen, Colletotrichum lindemuthianum , which has variable populations, the variation is not associated with geographical location (Mahuku & Riascos, ).…”

“…the sclerotinia stem rot pathogen Sclerotinia sclerotiorum (Ge et al, 2012)], or races [e.g. the blackleg pathogen Leptosphaeria maculans (Anonymous, 2013); and the white rust pathogen Albugo candida (Kaur et al, 2011)]. Generally, the internal transcribed spacer (ITS) region has been a useful region for molecular systematics, at both species and within species level, to identify such variation (Morales et al, 1993;Carter et al, 2002;Dubey et al, 2010;Kaur et al, 2011).…”

Valuable New Leaf or Inflorescence Resistances Ensure Improved Management of White Rust (Albugo candida) in Mustard (Brassica juncea) Crops

“…In Australia, Kaur et al. (, ) determined the hazard to the newly emerging B. juncea industry in Australia from races or pathotypes of A. candida present and Kaur et al. () determined race 2V to be the main race attacking B. juncea there; despite other strains isolated from Capsella bursa‐pastoris , B. oleracea , Raphanus raphanistrum and R. sativus also being pathogenic on B. juncea .…”

“…(, ) determined the hazard to the newly emerging B. juncea industry in Australia from races or pathotypes of A. candida present and Kaur et al. () determined race 2V to be the main race attacking B. juncea there; despite other strains isolated from Capsella bursa‐pastoris , B. oleracea , Raphanus raphanistrum and R. sativus also being pathogenic on B. juncea . A. candida commonly co‐occurs with the downy mildew pathogen, Hyaloperonospora parasitica and even asymptomatic colonization by H. parasitica , speeds up infection by A. candida and increases disease severity, even in a B. juncea variety with resistance to downy mildew (Kaur et al.…”

Selection of Host Differentials for the Identification of <I>Albugo candida</I> Pathotypes

“…Li et al (2008) varying levels of host resistance to Australian strains of A. candida (race 2) were identified among the genotypes from the three countries. Kaur et al (2011) clearly showed that the isolates obtained from B. juncea and R. raphanistrum are different in their host range. Petkowoski et al (2010) reported that A. candida races of Australian isolates from B. oleracea var.…”