Germplasm collections maintained by the US National Plant Germplasm System and those of other countries are critical sources of diversity utilized by breeders for crop improvement. This review summarizes status of collections and vulnerabilities for cucurbit crops.
The U.S. National Plant Germplasm System maintains a melon germplasm collection from worldwide melon production areas and regions where primitive melons exist. The CucCAP team genetically characterized the collection to increase understanding of genetic diversity, phylogenetic relationships, and population structure of the collection, and to improve melon taxonomic classifications. A core collection was developed from the analysis to provide a public resource for future research and genomics-assisted breeding. Thirty-five morphological characters were evaluated in the core collection to identify genomic regions potentially related to fruit quality and other horticultural traits important in melon improvement.
Downy mildew caused by Pseudoperonospora cubensis is the most destructive foliar disease affecting cucurbit crops. Genomic studies by Dr. Lina Quesada-Ocampo and colleagues at North Carolina State University showed that different isolates preferentially infect different cucurbit crops. From this information, a multiplex PCR-based assay was combined with spore trapping to identify which crops are most at risk. These results can facilitate timely and crop-specific fungicide application prior to appearance of symptoms in sentinel plots.
CucCAP researchers identified two major and seven minor QTL using a cross between the resistant melon breeding line MR-1 and susceptible cultivar Ananas Yoqne’am.
Umesh Reddy and team at WVSU and Amnon Levi and team at USDA, ARS used advance genome sequencing technology to study the effect of genome doubling on gene expression in tetraploid watermelon versus their counterpart diploid watermelon parental plants.
Resistance to CYSDV is exhibited by melon PI 313970, a vegetable type melon introduced from India.
Bacterial fruit blotch caused by Acidovorax citrulli is a serious disease of watermelon (Citrullus lanatus) in the U.S. Currently, there are no varieties resistant to the disease. In a 3-year study, 1452 accessions and cultivars were tested for resistance to fruit blotch at the immature fruit stage, where resistance is most important for growers.
In this study, researchers at Cornell collected 252 strains of the pathogen from across New York State and sequenced portions of their DNA in order to characterize the genetic structure of the pathogen population.