EXPLORING AND DEPLOYING GENETIC DIVERSITY FOR CUCUMBER, SQUASH, AND PEA IMPROVEMENT
Holdsworth, William Lee
This dissertation describes the development of germplasm and genomic resources aimed at addressing high-priority needs of growers and breeders of three regionally and globally important vegetable crops: cucumber (Cucumis sativus), squash (Cucurbita spp.), and pea (Pisum sativum). 1. Downy mildew is a disease that causes rapid plant death in cucumbers. A new strain of Pseudoperonospora cubensis, the causal oomycete agent of the disease, had overcome the resistance of all available commercial cultivars. Through a phenotypic selection-based breeding program, we developed new slicing cucumbers with high resistance to the disease, including ‘DMR-NY264’ and the earlier-maturing ‘DMR-NY401’. These lines outperformed commercial standard cultivars under disease pressure, and produced until the end of the season in the northeastern U.S. without fungicide application. 2. Powdery mildew, caused by the fungal pathogens Podosphaera xanthii and Golovinomyces cichoracearum, is the most prevalent disease worldwide on squash, and if unmanaged, can lead to decreased yield, fruit quality, and plant death. Although robust natural resistance is unknown in cultivated species, a gene from the wild species Cucurbita okeechobeensis subsp. martinezii was previously introgressed into all resistant commercial cultivars. To date, no markers have been published for this important gene. We used cultivar-based introgression mapping with SNP markers to map the Pm-0 locus to a 76.4 kb genomic interval, and this interval was validated with other mapping approaches. Several markers and candidate genes for Pm-0 are reported. 3. To date, genomic resources for pea improvement have been lacking. We assembled the USDA Pea Single Plant Plus Collection (PSPPC), a diverse core collection of peas to assist efforts towards trait mapping and genomics-assisted breeding. We used genotyping-by-sequencing to generate 66,591 SNPs that are publicly available. With this dataset, we identified sources of genetic diversity for breeding programs, demonstrated its utility for trait mapping by pinpointing the previously-cloned “A” locus controlling flower color, and constructed a smaller core collection which preserved the genetic diversity and minor alleles of the original collection.
core collection; cucumber; downy mildew; pea; powdery mildew; squash; Plant sciences
Gore, Michael; McCouch, Susan; Smart, Christine
Ph. D., Plant Breeding
Doctor of Philosophy
dissertation or thesis