Abstract
Quantitative trait locus (QTL) identification in perennial fruit crops is impeded largely by their lengthy generation time, resulting in costly and labor-intensive maintenance of breeding programs. In a grapevine (genus Vitis) breeding program, although experimental families are typically unreplicated, the genetic backgrounds may contain similar progenitors previously selected due to their contribution of favorable alleles. In this study, we investigated the utility of joint QTL identification provided by analyzing half-sib families. The genetic control of powdery mildew was studied using two half-sib F1 families, namely GE0711/1009 (MN1264 × MN1214; N = 147) and GE1025 (MN1264 × MN1246; N = 125) with multiple species in their ancestry. Maternal genetic maps consisting of 1077 and 1641 single nucleotide polymorphism (SNP) markers, respectively, were constructed using a pseudo-testcross strategy. Ratings of field resistance to powdery mildew were obtained based on whole-plant evaluation of disease severity. This 2-year analysis uncovered two QTLs that were validated on a consensus map in these half-sib families with improved precision relative to the parental maps. Examination of haplotype combinations based on the two QTL regions identified strong association of haplotypes inherited from ‘Seyval blanc’, through MN1264, with powdery mildew resistance. This investigation also encompassed the use of microsatellite markers to establish a correlation between 206-bp (UDV-015b) and 357-bp (VViv67) fragment sizes with resistance-carrying haplotypes. Our work is one of the first reports in grapevine demonstrating the use of SNP-based maps and haplotypes for QTL identification and tagging of powdery mildew resistance in half-sib families.
Highlights
Powdery mildew, caused by the biotrophic ascomycete Erysiphe necator, is a serious fungal disease of grapevine (Vitis spp.) worldwide (Gadoury et al 2012)
At the University of Minnesota grape breeding program, MN1264 is a quality hybrid wine grape that is not suited for production due to the production of only female flowers
In an effort to study the genetic determinism of powdery mildew resistance, MN1264 was used to construct two segregating mapping families, which are described in this study
Summary
Powdery mildew, caused by the biotrophic ascomycete Erysiphe necator, is a serious fungal disease of grapevine (Vitis spp.) worldwide (Gadoury et al 2012). It was rapidly spread to other regions where grapevines were cultivated. Cultivated Eurasian grapevine (Vitis vinifera L.) is susceptible to the fungus, which can infect all green tissues as well as inflorescences and immature fruit, resulting in yield losses due to reduced photosynthetic leaf area, poor fruit set, premature fruit drop, and diseased berries (Pearson 1988). Control of powdery mildew typically relies on frequent application of fungicides, which is becoming increasingly prohibitive due to their cost and adverse effects on human health and the environment. With modern grapevine cultivation moving toward sustainable practices, grape breeding for disease resistance offers potentially effective and environment-friendly control of powdery mildew. Marker-assisted breeding can expedite cultivar improvement for disease resistance by predicting the presence of resistance alleles when selecting parents or offspring
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