Abstract
Powdery mildew is a major fungal disease on squash and pumpkin (Cucurbita spp.) in the US and throughout the world. Genetic resistance to the disease is not known to occur naturally within Cucurbita pepo and only infrequently in Cucurbita moschata, but has been achieved in both species through the introgression of a major resistance gene from the wild species Cucurbita okeechobeensis subsp. martinezii. At present, this gene, Pm-0, is used extensively in breeding, and is found in nearly all powdery mildew-resistant C. pepo and C. moschata commercial cultivars. In this study, we mapped C. okeechobeensis subsp. martinezii-derived single nucleotide polymorphism (SNP) alleles in a set of taxonomically and morphologically diverse and resistant C. pepo and C. moschata cultivars bred at Cornell University that, by common possession of Pm-0, form a shared-trait introgression panel. High marker density was achieved using genotyping-by-sequencing, which yielded over 50,000 de novo SNP markers in each of the three Cucurbita species genotyped. A single 516.4 kb wild-derived introgression was present in all of the resistant cultivars and absent in a diverse set of heirlooms that predated the Pm-0 introgression. The contribution of this interval to powdery mildew resistance was confirmed by association mapping in a C. pepo cultivar panel that included the Cornell lines, heirlooms, and 68 additional C. pepo cultivars and with an independent F2 population derived from C. okeechobeensis subsp. martinezii x C. moschata. The interval was refined to a final candidate interval of 76.4 kb and CAPS markers were developed inside this interval to facilitate marker-assisted selection.
Highlights
Powdery mildew, caused by the obligate biotrophic pathogens Podosphaera xanthii and Golovinomyces cichoracearum, is one of the most prevalent and destructive fungal diseases globally of Cucurbita species, and especially of C. pepo, the most economically important species of squash and pumpkin [1,2,3,4,5]
Duane Bell was employed by Rupp Seeds Inc and received salary support during which time he generated and phenotyped the C. okeechobeensis subsp. martinezii PI 532363 x C. moschata ’Burpee’s Butterbush’ F2 population
We developed CAPS markers predictive of powdery mildew resistance from Pm-0 in both C. pepo and C. moschata backgrounds that can be used for marker-assisted breeding efforts in further development of powdery mildew-resistant squash and pumpkin cultivars
Summary
Powdery mildew, caused by the obligate biotrophic pathogens Podosphaera xanthii and Golovinomyces cichoracearum, is one of the most prevalent and destructive fungal diseases globally of Cucurbita species, and especially of C. pepo, the most economically important species of squash and pumpkin [1,2,3,4,5]. Introgression Mapping of Powdery Mildew Resistance in Squash pumpkin cultivars) during the time in which the manuscript was edited and in review. Rupp Seeds Inc. contributed resources for the analysis of the F2 population and support in the form of salaries for authors WLH and DB, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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