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Abstract
Wheat head blast is a dangerous fungal disease in South America and has recently spread to Bangladesh and Zambia, threatening wheat production in those regions. Host resistance as an economical and environment-friendly management strategy has been heavily relied on, and understanding the resistance loci in the wheat genome is very helpful to resistance breeding. In the current study, two recombinant inbred line (RIL) populations, Alondra/Milan (with 296 RILs) and Caninde#2/Milan-S (with 254 RILs and Milan-S being a susceptible variant of Milan), were used for mapping QTL associated with head blast resistance in field experiments. Phenotyping was conducted in Quirusillas and Okinawa, Bolivia, and in Jashore, Bangladesh, during the 2017–18 and 2018–19 cropping cycles. The DArTseq® technology was employed to genotype the lines, along with four STS markers in the 2NS region. A QTL with consistent major effects was mapped on the 2NS/2AS translocation region in both populations, explaining phenotypic variation from 16.7 to 79.4% across experiments. Additional QTL were detected on chromosomes 2DL, 7AL, and 7DS in the Alondra/Milan population, and 2BS, 4AL, 5AS, 5DL, 7AS, and 7AL in the Caninde#2/Milan-S population, all showing phenotypic effects <10%. The results corroborated the important role of the 2NS/2AS translocation on WB resistance and identified a few novel QTL for possible deployment in wheat breeding. The low phenotypic effects of the non-2NS QTL warrantee further investigation for novel QTL with higher and more stable effects against WB, to alleviate the heavy reliance on 2NS-based resistance.
Highlights
Wheat blast (WB) is an emerging fungal disease with great potentiality in causing large-scale yield reduction in the tropical and subtropical wheat production areas
WB vulnerable areas of 7 million ha were identified in India, Pakistan and Bangladesh, from where an annual yield reduction of 0.89–1.77 million tons of wheat may occur under WB conducive conditions (Mottaleb et al 2018)
In addition to the low effectiveness, the fast development of resistant fungal isolates is another factor to compromise fungicidal application, due to the high evolving rate of Magnaporthe oryzae pathotype Triticum (MoT) (Castroagudín et al 2015). This is a major difficulty for resistance breeding, and there have been many varieties initially identified as WB resistant that became susceptible in later experiments or in largescale cultivation (Cruz and Valent 2017)
Summary
Wheat blast (WB) is an emerging fungal disease with great potentiality in causing large-scale yield reduction in the tropical and subtropical wheat production areas. MoT can infect all the aerial parts of wheat, head blast on spikes is the most conspicuous symptom, often causing severe yield losses under favorable conditions on susceptible wheat varieties (Kohli et al 2011). In addition to the low effectiveness, the fast development of resistant fungal isolates is another factor to compromise fungicidal application, due to the high evolving rate of MoT (Castroagudín et al 2015). This is a major difficulty for resistance breeding, and there have been many varieties initially identified as WB resistant that became susceptible in later experiments or in largescale cultivation (Cruz and Valent 2017). Varietal resistance has been heavily relied on both in South America and South Asia, due to its low cost and ease of adoption, which is especially important for small-scale, resource-poor farmers having limited access to other WB management tools
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