Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2016
Publication Date: 2/1/2017
Citation: Branham, S., Levi, A., Farnham, M.W., Wechter, W.P. 2017. A genotype-by-sequencing-single nucleotide polymorphism based linkage map and quantitative trait loci (QTL) associated with resistance to Fusarium oxysporum f. sp. niveum race 2 identified in Citrullus lanatus var. citroides. Theoretical and Applied Genetics. 130: 319-330.
Interpretive Summary: Fusarium wilt devastates watermelon crop production worldwide. Several races of the pathogen exist with race 2 being one of the most destructive. Resistance to Fusarium wilt race 2 does not exist in the sweet cultivated watermelon and has only been found in a few wild subspecies of watermelon. ARS scientists in Charleston discovered a wild watermelon resistant to the race 2 strain and undertook research to study the underlying genetic control of this trait. This work resulted in the first genetic linkage map of a Fusarium wilt race 2 resistant wild watermelon generated by DNA sequence markers, and also the identification of specific markers associated with Fusarium wilt race 2 resistance in this important crop. This genetic map and associated markers will be important resources for use in incorporating Fusarium wilt resistance into sweet watermelon cultivars and is of great interest to public and private plant breeders working to make watermelon more disease resistant.
Technical Abstract: Fusarium wilt, a fungal disease caused by Fusarium oxysporum f. sp. niveum (Fon), devastates watermelon crop production worldwide. Several races, which are differentiated by host range, of the pathogen exist. Resistance to Fon race 2, a particularly virulent strain prevalent in the United States, does not exist in the sweet cultivated watermelon Citrullus lanatus var lanatus (Cll) and has only been found in a few plant introductions of the wild subspecies of watermelon, C. lanatus var. citroides (Clc). Clc provides a vital source of genetic diversity, as well as resistance to numerous diseases. Unfortunately both genetic diversity and disease resistance are lacking in Cll due to the narrow genetic base. Despite the importance of Clc to continued watermelon improvement, intra-variety genetic studies are lacking. Here, we present the first Clc genetic linkage map, generated with 2,495 single nucleotide polymorphisms developed through genotyping-by-sequencing, and use it to identify quantitative trait loci associated with Fon race 2 resistance. Multiple QTL mapping in a Clc F2:3 population (N=173) identified one major and four minor QTL. The major QTL explained 43% of the variation in Fon race 2 resistance and was delimited to a 1.2 Mb interval on chromosome 9, a region spanning 44 genes.