Evaluation of Australian Brassica napus genotypes for resistance to the downy mildew pathogen, Hyaloperonospora parasitica

Abstract

Downy mildew, caused by the pathogen Hyaloperonospora parasitica, is a severe disease of oilseed rape (Brassica napus) seedlings in some regions of Australia. Sixty-three cultivars of Australian spring-type oilseed rape were evaluated for their levels of resistance to five isolates of the downy mildew pathogen, using a cotyledon infection test under controlled-environment conditions. A high level of resistance, characterised by the absence of disease symptoms or only the appearance of very sparse sporulation on inoculated cotyledons, was expressed in cvv. Pioneer 45Y77 and Pioneer 46Y78. This is the first study to identify Australian genotypes of oilseed rape highly resistant to H. parasitica. The resistance to H. parasitica identified in this study will not only enable Australian oilseed rape breeders to incorporate resistance to H. parasitica into new cultivars for enhanced resistance to this disease, but will also allow direct deployment of the most highly resistant genotypes identified directly in situations and regions most conducive to the development of severe downy mildew disease.

Molecular characterization of disease resistance in Brassica juncea – The current status and the way forward

“…Downy mildew, caused by Hyaloperonospora brassicae (formerly Peronospora brassicae or Hyaloperonosporaparasitica), infects rapeseed-mustard in Canada, several Asian and European countries, including the UK and France, and also China and India (Saharan, 1993) and Australia (Ge et al, 2008). Downy mildew is an important disease in India, where the predominant oilseed brassica grown is B. juncea, and where it can cause serious economic loss even during the seedling stage (Thakur and Mathur, 2002 (Meena et al, 2014).…”

Current Status and Challenges in Identifying Disease Resistance Genes in Brassica napus

“…However, in some instances, there was association of resistance at cotyledon stage with that expressed at the adult stage (Jensen et al, 1999a ; Wang et al, 2000 ). Similarly, screening tests on seedling cotyledons across B. napus cultivars were claimed to provide an accurate estimation of expression of field susceptibilities/resistance on seedling and more mature leaves for Downy Mildew (Ge et al, 2008 ). These contrasting findings indicate that the resistance outcome in the host against Downy Mildew is likely to be QTL-specific where the QTL is associated with developmental stages of the plant.…”

Genome wide identification of NBS-LRR genes in Brassica and their association with disease resistance in Brassica napus

“…Several major qualitative resistance loci to downy mildew have been identified in B. rapa and B. oleracea (Farinhó et al, 2007, Carlier et al, 2012. In addition, multiple sources of resistance have been reported in B. napus (Nashaat et al, 1997, Ge et al, 2008. They showed that the resistance is more likely to be controlled by a major resistance gene.…”

“…While it causes severe destruction on young seedlings, the disease still causes yield and quality reduction at adult-plant stages. For instance, in Australia, outbreaks of downy mildew disease at the early seedling stage have caused losses of canola production (Ge et al, 2008). Several major qualitative resistance loci to downy mildew have been identified in B. rapa and B. oleracea (Farinhó et al, 2007, Carlier et al, 2012.…”

“…In B. rapa, three resistance loci were found, BraDM on chromosome A8 , Yu et al, 2011b, the BrRHP1 locus on chromosome A1 and candidate resistance gene locus RPP13MK on chromosome A9 (Yu et al, 2010). In addition, multiple sources of resistance have been reported in B. napus (Nashaat et al, 1997, Ge et al, 2008.…”