Abstract
Sclerotinia stem rot (SSR) is a fungal disease of rapeseed/canola that causes significant seed yield losses and reduces its oil content and quality. In the present study, the reaction of 187 diverse canola genotypes to SSR was characterized at full flowering stage using the agar plug to stem inoculation method in four environments. Genome-wide association study (GWAS) using three different algorithms identified 133 significant SNPs corresponding with 123 loci for disease traits like stem lesion length (LL), lesion width (LW), and plant mortality at 14 (PM_14D) and 21 (PM_21D) days. The explained phenotypic variation of these SNPs ranged from 3.6 to 12.1%. Nineteen significant SNPs were detected in two or more environments, disease traits with at least two GWAS algorithms. The strong correlations observed between LL and other three disease traits evaluated, suggest they could be used as proxies for SSR resistance phenotyping. Sixty-nine candidate genes associated with disease resistance mechanisms were identified. Genomic prediction (GP) analysis with all the four traits employing genome-wide markers resulted in 0.41–0.64 predictive ability depending on the model specifications. The highest predictive ability for PM_21D with three models was about 0.64. From our study, the identified resistant genotypes and stable significant SNP markers will serve as a valuable resource for future SSR resistance breeding. Our study also suggests that genomic selection holds promise for accelerating canola breeding progress by enabling breeders to select SSR resistance genotypes at the early stage by reducing the need to phenotype large numbers of genotypes.
Highlights
Sclerotinia sclerotiorum (Lib.) de Bary is a devastating non-host specific, necrotrophic and ubiquitous plant pathogenic fungus that infects at least 408 plant species including economically important dicotyledonous crops such as oilseed rape, edible dry bean, soybean, sunflower, pea, chickpea, lentils, and different types of vegetables and some monocotyledonous crops such as tulip and o nion[1,2]
Source of completely durable genetically resistant genotypes against this disease have not been identified to date in rapeseed/canola, breeding for Sclerotinia stem rot (SSR) resistance is primarily dependent to a large extent on the utilization of partially resistant s ource[15,16]
We explored our rapeseed/canola diversity panel, including released cultivars, advanced breeding lines, and landraces from the different geographical regions with high genetic diversity against SSR in field trials conducted in four environments by inoculating plants artificially
Summary
Sclerotinia sclerotiorum (Lib.) de Bary is a devastating non-host specific, necrotrophic and ubiquitous plant pathogenic fungus that infects at least 408 plant species including economically important dicotyledonous crops such as oilseed rape, edible dry bean, soybean, sunflower, pea, chickpea, lentils, and different types of vegetables and some monocotyledonous crops such as tulip and o nion[1,2]. The disease caused by this pathogen in rapeseed/ canola is commonly referred to as sclerotinia stem rot (SSR), and it significantly limits rapeseed yield/production worldwide. It is crucial to study different germplasm from diverse regions in order to unravel the nature of durable genetic resistance and identify responsible genes for the resistance to S. sclerotiorum Such identified SSR resistance genes can be introduced into high performing elite canola cultivars which diminish the dependence of the canola growers on cultural practices and use of fungicides and making canola production more profitable. Integration and comparative analyses of the previously identified resistance QTLs from various mapping studies with the reference genome sequence have detected conserved QTLs on chromosome A9 (22.5–27.5 Mb) and C6 (29.5–36.1 Mb)[26] Despite these successes, no fine mapping or map-based cloning for sclerotinia resistance gene has been reported so far, which circumvents the utilization of identified QTL in the SSR resistance breeding strategy. Derbyshire et al.[41] implemented GP on adult plant SSR resistance in B. napus and reported that the GS can be used for the improvement of S. sclerotiorum resistance
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