Location: Vegetable ResearchTitle: Genome-wide association analysis of resistance to Pseudoperonospora cubensis in citron watermelon
|BRANHAM, SANDRA - Clemson University|
|Wechter, William - Pat|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2021
Publication Date: 6/13/2022
Citation: Katuuramu, D.N., Branham, S.E., Levi, A., Wechter, W.P. 2022. Genome-wide association analysis of resistance to Pseudoperonospora cubensis in citron watermelon. Plant Disease. 106:1952-1958. https://doi.org/10.1094/PDIS-08-21-1611-RE.
Interpretive Summary: Watermelon is an important vegetable crop in the United States and around the world. Cucurbit downy mildew (CDM) is a serious threat to the production of cucumber, cantaloupes, and watermelon in the U.S as well as in other cucurbits growing areas around the world. New sources of resistance and molecular markers are needed to control the spread of CDM pathogen in watermelon. To date, no genetic studies on resistance to CDM have been conducted in watermelon. In this research, we screened a USDA citron watermelon (close relative of the cultivated sweet watermelon) collection for resistance to a virulent isolate of CDM identifying several plant introductions with resistance to this pathogen. Using a genetic mapping technique called genome-wide association study, we identified genomic markers and candidate genes linked to resistance to CDM. These new molecular markers and resistant USDA plant introductions will be useful in breeding watermelon for resistance to CDM.
Technical Abstract: Cultivated sweet watermelon (Citrullus lanatus) is an important vegetable crop for millions of people around the world. There are limited sources of resistance to economically important diseases within C. lanatus, whereas Citrullus amarus has a reservoir of traits that can be exploited to improve C. lanatus for resistance to biotic and abiotic stresses. Cucurbit downy mildew (CDM), caused by Pseudoperonospora cubensis, is an emerging threat to watermelon production. We screened 122 C. amarus accessions for resistance to CDM over two tests (environments). The accessions were genotyped by whole-genome resequencing to generate 2,126,759 single nucleotide polymorphic (SNP) markers. A genome-wide association study was deployed to uncover marker-trait associations and identify candidate genes underlying resistance to CDM. Our results indicate the presence of wide phenotypic variability (1.1 - 57.8%) for leaf area infection, representing a 50.7-fold variation for CDM resistance across the C. amarus germplasm collection. Broad-sense heritability estimate was 0.55, implying the presence of moderate genetic effects for resistance to CDM. The peak SNP markers associated with resistance to P. cubensis were located on chromosomes Ca03, Ca05, Ca07, and Ca11. The significant SNP markers accounted for up to 30% of the phenotypic variation and were associated with promising candidate genes encoding disease resistance proteins, leucine-rich repeat receptor-like protein kinase, and WRKY transcription factor. This information will be useful in understanding the genetic architecture of the P. cubensis-Citrullus spp. patho-system as well as development of resources for genomics-assisted breeding for resistance to CDM in watermelon.