Abstract
Sclerotinia Head Rot (SHR), a disease caused by Sclerotinia sclerotiorum, is one of the most limiting factors in sunflower production. In this study, we identified genomic loci associated with resistance to SHR to support the development of assisted breeding strategies. We genotyped 114 Recombinant Inbred Lines (RILs) along with their parental lines (PAC2 –partially resistant–and RHA266 –susceptible–) by using a 384 single nucleotide polymorphism (SNP) Illumina Oligo Pool Assay to saturate a sunflower genetic map. Subsequently, we tested these lines for SHR resistance using assisted inoculations with S. sclerotiorum ascospores. We also conducted a randomized complete-block assays with three replicates to visually score disease incidence (DI), disease severity (DS), disease intensity (DInt) and incubation period (IP) through four field trials (2010–2014). We finally assessed main effect quantitative trait loci (M-QTLs) and epistatic QTLs (E-QTLs) by composite interval mapping (CIM) and mixed-model-based composite interval mapping (MCIM), respectively. As a result of this study, the improved map incorporates 61 new SNPs over candidate genes. We detected a broad range of narrow sense heritability (h2) values (1.86–59.9%) as well as 36 M-QTLs and 13 E-QTLs along 14 linkage groups (LGs). On LG1, LG10, and LG15, we repeatedly detected QTLs across field trials; which emphasizes their putative effectiveness against SHR. In all selected variables, most of the identified QTLs showed high determination coefficients, associated with moderate to high heritability values. Using markers shared with previous Sclerotinia resistance studies, we compared the QTL locations in LG1, LG2, LG8, LG10, LG11, LG15 and LG16. This study constitutes the largest report of QTLs for SHR resistance in sunflower. Further studies focusing on the regions in LG1, LG10, and LG15 harboring the detected QTLs are necessary to identify causal alleles and contribute to unraveling the complex genetic basis governing the resistance.
Highlights
Sclerotinia sclerotiorum (Lib.) de Bary is a widespread fungal pathogen in sunflower regions of the world [1]
For disease incidence (DI), we found six M-quantitative trait loci (QTL) located on LG1, LG7, LG13, LG14 and LG15
For disease intensity (DInt), we found 12 main-effect QTLs (M-QTLs) located on LG1, LG8, LG10, LG11, LG12, LG13 and LG15, 11 detected by single-locus analysis and one by two-locus analysis; none in common
Summary
Sclerotinia sclerotiorum (Lib.) de Bary is a widespread fungal pathogen in sunflower regions of the world [1] It produces head rot, stalk rot, and wilt, among other diseases. Sclerotinia Head Rot (SHR) is one of the most common and damaging diseases in Argentina, Canada, China, Europe, South Africa and the United States. This disease accounts for 10 to 20% of average yield reduction in sunflower production, while in a season where humidity and temperature are both favorable for disease progression, SHR can produce the loss of the entire harvest [2]. The genetic basis of SHR resistance has been described as consisting of many genes of small quantitative effects whose expressions are highly dependent on the environment with different mechanisms involved in resistance at each phase of the disease in sunflower [4]
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