A GBS-SNP-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
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A major QTL for resistance to Fusarium oxysporum f. sp. niveum race 2 was mapped to a narrow 1.2 Mb interval using a high-density GBS-SNP linkage map, the first map of Citrullus lanatus var. citroides.
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 edible cultivars of the sweet cultivated watermelon Citrullus lanatus var. lanatus (Cll) and has been well described 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 2495 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.
KeywordsQuantitative Trait Locus Fusarium Wilt Plant Introduction Resistance Allele Major Quantitative Trait Locus
This study was funded by the United States Department of Agriculture, project no. 6080-22000-025-00 and the National Institute of Food and Agriculture, project no. 6080-21000-018-08. We would like to acknowledge and thank Dr. Yong Xu and Honghe Sun of National Engineering Research Center for Vegetables, China and Dr. Zhangjun Fei of USDA-ARS, Boyce Thompson Institute, Cornell University, USA for providing the genome information for Citrullus lanatus var citroides PI 296341.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
The experiment conducted complies with the laws of the United States.
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