Breeding for Resistance: Genetic Mapping and Identification of Powdery Mildew Resistance in Squash

Commodities

Practices

The goal of this project is to introduce a new source of genetic resistance (PM-B) against powdery mildew (PM) into squash cultivars, which will help reduce dependence on fungicides and support more sustainable farming practices. This work builds on the PI's earlier Ph.D. research completed in 2018, where a potential resistance gene was identified in squash. Powdery mildew is one of the major issues affecting squash production in the U.S., a crop that holds both economic and culinary value. Currently, only one genetic resistance source is being used widely in squash, which gives only partial protection. So, growers mostly rely on fungicide sprays to manage PM, which adds to production costs and poses environmental risks, especially to aquatic ecosystems. Also, with continuous use, fungicide resistance in pathogens is becoming a real concern. Relying on just one resistance gene puts pressure on the pathogen population and increases the chance of breakdown of resistance.

In this project, we aim to genetically characterize the novel resistance gene to understand how it works and then try to introgress it into an elite cultivated variety through breeding methods. Starting in fall 2025, we'll carry out transcriptomic analysis, fine mapping, and field screening. A Ph.D. student will assist in both molecular lab work and field trials.

By identifying and transferring this resistance gene into squash cultivars, we hope to create varieties that require less fungicide use ultimately benefiting farmers economically and reducing negative environmental impacts, pushing us a step closer to sustainable agriculture.

The broad objective of this project is to introduce two new sources of powdery mildew resistance into elite cultivated varieties of squash, ultimately bringing improved, resistant varieties to the market. Based on promising results from preliminary experiments, this project will focus exclusively on the Pm-B gene. To accomplish this, we have outlined two specific objectives.

1. The first objective is to map the causal gene(s) associated with Pm-B, a novel source of powdery mildew resistance. To achieve this, we will use a mapping population to conduct phenotypic characterization, assessing disease development and severity following powdery mildew infection. In parallel, we plan to perform genotyping of the Pm-B gene through a Genotyping by Sequencing approach (GBS). This will be followed by quantitative trait locus (QTL) analysis and marker interval refinement to narrow down the genomic region of interest. Finally, we will identify candidate genes through gene expression analysis, providing a deeper understanding of the genetic basis for resistance.
2. The second objective is the transfer of the Pm-B gene into elite lines of winter squash, summer squash, and ornamental pumpkins. This process will involve crossing the powdery mildew resistance source with carefully selected bridge lines to ensure both fertility and successful inheritance of the resistance trait. Subsequent backcrossing and will be directed toward introgressing the resistance into an elite cultivated squash variety. Marker-assisted selection will be applied during the crossing process to efficiently track and retain the resistance gene.

By pursuing these two objectives, we aim to develop new squash cultivars with durable resistance to powdery mildew, supporting growers with improved plant health and reducing the reliance on chemical controls.