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QTL mapping of powdery mildew resistance in WI 2757 cucumber (Cucumis sativus L)

Yiqun Weng
Theoretical and applied genetics 2013 v.126 pp. 2149-2161
Cucumis sativus, chromosome mapping, chromosomes, cotyledons, cucumbers, cultivars, disease resistance, genetic markers, hosts, hypocotyls, leaves, linkage groups, marker-assisted selection, microsatellite repeats, phenotypic variation, powdery mildew, quantitative trait loci, recessive genes
Powdery mildew is a serious fungal disease of cucumber and other cucurbot crops in the US and many other parts of the world. Resistant cultivars have been deployed in production for a long time, but the genetic mechanisms of powdery mildew resistance in cucumber are not well understood. In a three-year study, we conducted QTL mapping of powdery mildew resistance with 132 F2:3 families derived from two cucumber inbred lines WI 2757 (resistant) and True Lemon (susceptible). A genetic map with seven linkage groups was developed with 240 microsatellite marker loci. QTL mapping of hypocotyl, cotyledon and true leaf for responses to PM inoculation identified seven genomic regions in four chromosomes that were associated with PM resistance in WI 2757. Among the seven QTL detected, pm1.1 and pm1.2 in chromosome 1 conferred leaf resistance. Minor QTL Pm3.1 (chromosome 3) and Pm4.1 (chromosome 4) contributed to disease susceptibility. The three major QTL, pm5.1, pm5.2 and pm5.3 were located in an interval of ~ 40 cM on chromosome 5 with each explaining 21.0-74.5% phenotypic variations. Our study support three recessively inherited, linked major QTL in Chromosome 5 plus minor QTL in other three chromosomes that control the PM resistance in WI 2757. The QTL pm5.3 for hypocotyl resistance plays the most important role in host resistance. Results from this study provided new insights into phenotypic and genetic mechanisms of powdery mildew resistance in cucumber. Molecular markers developed are also useful in marker-assisted selection for powdery mildew resistance in cucumber breeding.