Abstract
Key messageGenome-wide association mapping in conjunction with population sequencing map and Ensembl plants was used to identify markers/candidate genes linked to leaf rust, stripe rust and tan spot resistance in wheat.Leaf rust (LR), stripe rust (YR) and tan spot (TS) are some of the important foliar diseases in wheat (Triticum aestivum L.). To identify candidate resistance genes for these diseases in CIMMYT’s (International Maize and Wheat Improvement Center) International bread wheat screening nurseries, we used genome-wide association studies (GWAS) in conjunction with information from the population sequencing map and Ensembl plants. Wheat entries were genotyped using genotyping-by-sequencing and phenotyped in replicated trials. Using a mixed linear model, we observed that seedling resistance to LR was associated with 12 markers on chromosomes 1DS, 2AS, 2BL, 3B, 4AL, 6AS and 6AL, and seedling resistance to TS was associated with 14 markers on chromosomes 1AS, 2AL, 2BL, 3AS, 3AL, 3B, 6AS and 6AL. Seedling and adult plant resistance (APR) to YR were associated with several markers at the distal end of chromosome 2AS. In addition, YR APR was also associated with markers on chromosomes 2DL, 3B and 7DS. The potential candidate genes for these diseases included several resistance genes, receptor-like serine/threonine-protein kinases and defense-related enzymes. However, extensive LD in wheat that decays at about 5 × 107 bps, poses a huge challenge for delineating candidate gene intervals and candidates should be further mapped, functionally characterized and validated. We also explored a segment on chromosome 2AS associated with multiple disease resistance and identified seventeen disease resistance linked genes. We conclude that identifying candidate genes linked to significant markers in GWAS is feasible in wheat, thus creating opportunities for accelerating molecular breeding.
Highlights
Leaf rust or brown rust (LR) caused by Puccinia triticina Eriks., stripe rust or yellow rust (YR) caused by Puccinia striiformis West., and tan spot (TS) caused by Pyrenophora tritici-repentis (Died.) Shoemaker are some of the important foliar diseases in wheat (Triticum aestivum L.)
The mean YR severities on a 0–100% severity scale were only 5.5 ± 8.8 (Quito 2012), 6.1 ± 6.6 (Njoro 2011), 2 ± 3.2 (Toluca 2011) and 8.7 ± 6.5 (Toluca 2013), despite high disease pressures leading to 100% severity for the susceptible check
The two most significant markers for seedling resistance to LR were located on chromosome 1DS
Summary
Leaf rust or brown rust (LR) caused by Puccinia triticina Eriks., stripe rust or yellow rust (YR) caused by Puccinia striiformis West., and tan spot (TS) caused by Pyrenophora tritici-repentis (Died.) Shoemaker are some of the important foliar diseases in wheat (Triticum aestivum L.). LR is the most common disease in many wheat-producing areas of the world and can cause substantial yield losses (Marasas et al 2004), due to reduced kernel number and kernel weight. YR is a serious disease that is prevalent in the temperate regions and results in yield losses ranging from 10 to 70% (Chen 2005). Besides these rusts, another foliar disease that is globally distributed and economically significant is TS (De Wolf et al 1998), that can cause yield losses ranging from 18 to 31% under favorable conditions (Bhathal et al 2003). While fungicides and agronomic practices are available for the management of these diseases, the deployment of resistant cultivars is the most economical and effective strategy
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