Abstract
BackgroundSclerotinia Head Rot (SHR) is one of the most damaging diseases of sunflower in Europe, Argentina, and USA, causing average yield reductions of 10 to 20 %, but leading to total production loss under favorable environmental conditions for the pathogen. Association Mapping (AM) is a promising choice for Quantitative Trait Locus (QTL) mapping, as it detects relationships between phenotypic variation and gene polymorphisms in existing germplasm without development of mapping populations. This article reports the identification of QTL for resistance to SHR based on candidate gene AM.ResultsA collection of 94 sunflower inbred lines were tested for SHR under field conditions using assisted inoculation with the fungal pathogen Sclerotinia sclerotiorum. Given that no biological mechanisms or biochemical pathways have been clearly identified for SHR, 43 candidate genes were selected based on previous transcript profiling studies in sunflower and Brassica napus infected with S. sclerotiorum. Associations among SHR incidence and haplotype polymorphisms in 16 candidate genes were tested using Mixed Linear Models (MLM) that account for population structure and kinship relationships. This approach allowed detection of a significant association between the candidate gene HaRIC_B and SHR incidence (P < 0.01), accounting for a SHR incidence reduction of about 20 %.ConclusionsThese results suggest that AM will be useful in dissecting other complex traits in sunflower, thus providing a valuable tool to assist in crop breeding.
Highlights
Sclerotinia Head Rot (SHR) is one of the most damaging diseases of sunflower in Europe, Argentina, and USA, causing average yield reductions of 10 to 20 %, but leading to total production loss under favorable environmental conditions for the pathogen
This paper reports the identification of resistance Quantitative Trait Locus (QTL) for SHR based on candidate gene Association Mapping (AM)
Given that no biological mechanisms or biochemical pathways have been positively identified for SHR, selection of candidate genes was based on previous transcript profiling studies in sunflower [36,37,38] and B. napus [25]. This approach resulted successful in detecting a significant association between one of the candidate genes evaluated and SHR incidence. These results suggest that AM is a useful strategy for dissecting complex traits in sunflower, providing a valuable tool to assist in crop breeding
Summary
Sclerotinia Head Rot (SHR) is one of the most damaging diseases of sunflower in Europe, Argentina, and USA, causing average yield reductions of 10 to 20 %, but leading to total production loss under favorable environmental conditions for the pathogen. Sclerotinia sclerotiorum (Lib) de Bary is a worldwide distributed necrotrophic pathogen, attacking more than 400 plant species including sunflower, soybean and rapeseed [2,3]. The fungus can attack several plant organs causing diverse symptoms in leaves, stalks and flowers, with Sclerotinia Head Rot (SHR) being the most damaging for sunflower crop production. SHR is considered a major disease in Europe, Argentina, and USA, causing average yield reductions of 10 to 20 %, and can even result in loss of the entire harvest [4,5]. Disease control on S. sclerotiorum is difficult, since the fungus persists in soils for long periods and at high inoculum levels [6,7,8]
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