Abstract
Alternaria brassicae, a necrotrophic fungal pathogen, causes Alternaria blight, one of the most important diseases of oleiferous Brassica crops. The current study utilized Arabidopsis as a model to decipher the genetic architecture of defense against A. brassicae. Significant phenotypic variation that was largely genetically determined was observed among Arabidopsis accessions in response to pathogen challenge. Three biparental mapping populations were developed from three resistant accessions viz. CIBC-5, Ei-2, and Cvi-0 and two susceptible accessions – Gre-0 and Zdr-1 (commonly crossed to CIBC-5 and Ei-2). A total of six quantitative trait locus (QTLs) governing resistance to A. brassicae were identified, five of which were population-specific while one QTL was common between all the three mapping populations. Interestingly, the common QTL had varying phenotypic contributions in different populations, which can be attributed to the genetic background of the parental accessions. The presence of both common and population-specific QTLs indicate that resistance to A. brassicae is quantitative, and that different genes may mediate resistance to the pathogen in different accessions. Two of the QTLs had moderate-to-large effects, one of which explained nearly 50% of the variation. The large effect QTLs may therefore contain genes that could play a significant role in conferring resistance even in heterologous hosts.
Highlights
Alternaria spp. are serious necrotrophic plant pathogens, causing a range of diseases in many crops including the Brassica species
Three different mapping populations were developed from the highly resistant and susceptible accessions to dissect the genetic basis of resistance to A. brassicae
The work reported here explores the genetics of resistance to the necrotrophic pathogen A. brassicae in Arabidopsis by using three different biparental populations to map the underlying components imparting resistance
Summary
Alternaria spp. are serious necrotrophic plant pathogens, causing a range of diseases in many crops including the Brassica species. The most common and destructive diseases of the Brassica crops worldwide are caused by four species of Alternaria viz. Alternaria brassicae, Alternaria brassicicola, Alternaria raphani, and Alternaria alternata (Verma and Saharan, 1994). A. brassicae is the most invasive on all brassicaceous hosts, though it infects the oil-yielding brassicas preferentially. In the Indian subcontinent, A. brassicae is recognized as one of the most important pathogens on oilseed Brassica species, especially Brassica juncea (Grover and Pental, 2003). Genetic Architecture of Resistance to Alternaria brassicae in Arabidopsis thaliana reduction in photosynthetic potential; results in abnormal seed development, and a reduction in seed oil content and quality leading to 10–71% yield losses worldwide (Saharan et al, 2015). Extensive screening of B. juncea germplasm has shown a lack of complete resistance to A. brassicae
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