Abstract
Spot blotch (SB) of wheat is emerging as a major threat to successful wheat production in warm and humid areas of the world. SB, also called leaf blight, is caused by Bipolaris sorokiniana, and is responsible for high yield losses in Eastern Gangetic Plains Zone in India. More recently, SB is extending gradually toward cooler, traditional wheat-growing North-Western part of the country which is a major contributor to the national cereal basket. Deployment of resistant cultivars is considered as the most economical and ecologically sound measure to avoid losses due to this disease. In the present study, 89 backcross introgression lines (DSBILs) derived from Triticum durum (cv. PDW274-susceptible) × Aegilops speltoides (resistant) were evaluated against SB for four consecutive years, 2016–2020. Phenotypic evaluation of these lines showed a continuous variation in disease severity indicating that the resistance to SB is certainly quantitative in nature. Phenotypic data of DSBILs were further used for mapping QTLs using SNPs obtained by genotyping by sequencing. To identify QTLs stable across the environments, Best Linear Unbiased Estimates (BLUEs) and Predictions (BLUPs) were used for mapping QTLs based on stepwise regression-based Likelihood Ratio Test (RSTEP-LRT) for additive effect of markers and single marker analysis (SMA). Five QTLs, Q.Sb.pau-2A, Q.Sb.pau-2B, Q.Sb.pau-3B, Q.Sb.pau-5B, and Q.Sb.pau-6A, linked to SB resistance were mapped across chromosomes 2A, 2B, 3B, 5B, and 6A. Genes found adjacent to the SNP markers linked to these QTLs were literature mined to identify possible candidate genes by studying their role in plant pathogenesis. Further, highly resistant DSBIL (DSBIL-13) was selected to cross with a susceptible hexaploidy cultivar (HD3086) generating BC2F1 population. The QTL Q.Sb.pau-5B, linked to SNP S5B_703858864, was validated on this BC2F1 population and thus, may prove to be a potential diagnostic marker for SB resistance.
Highlights
Wheat, a major food crop of the world population, is in a constant threat from various biotic and abiotic stresses, limiting its potential for yield
The DSBIL panel used in the present study showed wide range of variation for different traits and has already been reported to possess various QTLs for heat tolerance, stripe rust, and powdery mildew resistance (Awlachew et al, 2016; Dhillon et al, 2020)
Because no wheat cultivar presently grown in North-Western plains of India possess resistance to spot blotch (SB), these lines become an important resource for transfer of SB resistance
Summary
A major food crop of the world population, is in a constant threat from various biotic and abiotic stresses, limiting its potential for yield. Helminthosporium leaf blight/foliar blight/spot blotch (SB), caused by Cochliobolus sativus (anamorph: Bipolaris sorokiniana), is a major foliar disease of wheat in warmer wheat-growing regions This hemibiotrophic fungus can potentially infect and damage various species of Poaceae family (Gupta et al, 2018). An estimated 25 million ha of wheat land is affected by SB (Yadav et al, 2015), out of which around 10 million ha is in the Indian Subcontinent and 9 million ha of this is in the North-Eastern Plain Zone of India (Duveiller and Sharma, 2012; Chowdhury et al, 2013) This disease is extending gradually toward the North-West part characterized by high temperature and humidity late in the season (Saari, 1998) with an average yield loss of about 15–20% (Chand et al, 2003). It is a seed-transmitted disease and the conidia can survive in the soil
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