Qtl mapping and molecular markers of powdery mildew resistance in pumpkin (Cucurbita moschata)

Cucurbita moschata, an economically and nutritionally important vegetable in Korea, is seriously damaged in fruit quality and productivity by powdery mildew fungus (Podosphaera xanthii). To understand genetic bases of the powdery mildew disease resistance, an F₂ population was developed from a cross between TG201 (C. moschata, susceptible, female parent) and TG10 (resistant, male parent) heirloom from Hongikbio Inc. Randomly selected 204 F₂ individuals were assayed against powdery mildew pathogen, and construction of genetic map and QTL analysis were conducted using SNPs derived from genotyping-by-sequencing (GBS) method. The single major QTL was located in 6.9 - 7.3 Mb region of TG10 chromosome 3. Within the 400 kb region, we investigated DNA insertion and deletion (indel) variations between TG201 and TG10 genome, and successfully designed seven sets of indel PCR markers. The functional validity of the powdery mildew resistance markers was confirmed with F2 individuals, breeding lines, and commercial varieties. From genomic sequence comparison on the basis of the breeding history, we also could clarify that the powdery mildew resistance region was introduced from C. okeechobeensis subsp. martinezii to C. moschata. Moreover, whole genome assemblies of two heirloom parents and genome-wide SNP/indel information were produced and are expected to be utilized as a genome resource for study of genus Cucurbita. The results and information of this study will be useful for genetics researches and breeding practices of C. moschata.