Identification of QTLs for resistance to powdery mildew (Erysiphe) in red clover (Trifolium pratense)

Abstract

To locate quantitative trait loci (QTLs) resistant to powdery mildew (Erysiphe), a major disease of red clover, 151 red clover hybrids from crosses between genotypes from a resistant (Ganong PR1) and a susceptible (Minshan) cultivar were used as the mapping population. A genetic linkage map of red clover was constructed, and 30 plants with disease severity levels on a scale of one to nine, were used to locate QTLs correlated with resistance to powdery mildew. A genetic map that included seven linkage groups (LG1–7) was constructed based on 149 amplified fragment length polymorphic markers. QTLs associated with the resistance to powdery mildew were located using the multiple interval mapping method. The linkage map covered 640.5 cM, with an average distance of 4.3 cM between markers. LG1 was the largest (140.6 cM), with the average distance between markers, while LG4 was the smallest (55.2 cM) but had the highest marker density, with a 1.8-cM average distance between markers. Five QTLs (qrp-1–5) correlated with resistance to powdery mildew were located on LG4 and LG5. The phenotypic variance explained by these five QTLs ranged from 29% to 90%, with qrp-1 having the greatest contribution. Therefore, qrp-1 was identified as the main candidate gene controlling resistance to powdery mildew in red clover. This study provides a foundation in red clover for locating genes, transgenesis and marker-assisted breeding.