Abstract
Spot blotch caused by the fungus Bipolaris sorokiniana poses a serious threat to bread wheat production in warm and humid wheat-growing regions of the world. Hence, the major objective of this study was to identify consistent genotyping-by-sequencing (GBS) markers associated with spot blotch resistance using genome-wide association mapping on a large set of 6,736 advanced bread wheat breeding lines from the International Maize and Wheat Improvement Center. These lines were phenotyped as seven panels at Agua Fria, Mexico between the 2013–2014 and 2019–2020 crop cycles. We identified 214 significant spot blotch associated GBS markers in all the panels, among which only 96 were significant in more than one panel, indicating a strong environmental effect on the trait and highlights the need for multiple phenotypic evaluations to identify lines with stable spot blotch resistance. The 96 consistent GBS markers were on chromosomes 1A, 1B, 1D, 2A, 3B, 4A, 5B, 5D, 6B, 7A, 7B, and 7D, including markers possibly linked to the Lr46, Sb1, Sb2 and Sb3 genes. We also report the association of the 2NS translocation from Aegilops ventricosa with spot blotch resistance in some environments. Moreover, the spot blotch favorable alleles at the 2NS translocation and two markers on chromosome 3BS (3B_2280114 and 3B_5601689) were associated with increased grain yield evaluated at several environments in Mexico and India, implying that selection for favorable alleles at these loci could enable simultaneous improvement for high grain yield and spot blotch resistance. Furthermore, a significant relationship between the percentage of favorable alleles in the lines and their spot blotch response was observed, which taken together with the multiple minor effect loci identified to be associated with spot blotch in this study, indicate quantitative genetic control of resistance. Overall, the results presented here have extended our knowledge on the genetic basis of spot blotch resistance in bread wheat and further efforts to improve genetic resistance to the disease are needed for reducing current and future losses under climate change.
Highlights
Spot blotch or Helminthosporium leaf blight caused by the hemi-biotrophic fungus Bipolaris sorokiniana (Sacc.) Shoemaker [teleomorph: Cochliobolus sativus (Ito and Kuribayashi) Drechsler ex Dastur], is a major constraint to bread wheat (Triticum aestivum) production in warm and humid wheatgrowing regions of the world, threatening the livelihoods of numerous small-holder farmers (Dubin and Van Ginkel, 1991; Duvellier and Gilchrist, 1994; Duveiller et al, 1997; Saari, 1998; Duveiller and Sharma, 2009; Gupta et al, 2018)
Low to high negative correlations were observed between the spot blotch relative AUDPC (rAUDPC) values and days to heading in the different panels that ranged between −0.18 and −0.66 and were highly significant at a p-value threshold of 0.001
The correlations between spot blotch rAUDPC values and height were significant at a p-value threshold of 0.001 in only panel 2015 and panel 2016
Summary
Spot blotch or Helminthosporium leaf blight caused by the hemi-biotrophic fungus Bipolaris sorokiniana (Sacc.) Shoemaker [teleomorph: Cochliobolus sativus (Ito and Kuribayashi) Drechsler ex Dastur], is a major constraint to bread wheat (Triticum aestivum) production in warm and humid wheatgrowing regions of the world, threatening the livelihoods of numerous small-holder farmers (Dubin and Van Ginkel, 1991; Duvellier and Gilchrist, 1994; Duveiller et al, 1997; Saari, 1998; Duveiller and Sharma, 2009; Gupta et al, 2018). The disease is typically characterized by small dark brown lesions of 1–2 mm length, that extend to form elongated light to dark brown blotches of several centimeters before coalescing and causing leaf necrosis (Mercado Vergnes et al, 2006; Duveiller and Sharma, 2009). This pathogen induced foliar necrosis reduces the photosynthetic area of the leaf and results in premature senescence (Sharma et al, 1997). The pathogen can infect the spikes, resulting in shriveling of the grain, black point of the kernels and deterioration of grain quality (Sharma et al, 1997; Kumar et al, 2002)
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