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Research Project: Genetic Enhancement of Watermelon, Broccoli, and Leafy Brassicas for Economically Important Traits

Location: Vegetable Research

Title: Genetic mapping and identification of quantitative trait loci associated with resistance to Fusarium oxysporum f. sp. niveum races 1 and 2 in watermelon

Author
item Wechter, William - Pat
item Branham, Sandra
item Lambel, Shuanese - Hm-Clause
item Guner, Nihat - Sakata Seed America, Inc
item Levi, Amnon

Submitted to: Cucurbitaceae Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/21/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: N/A

Technical Abstract: Fusarium wilt is a major disease of watermelon caused by the soil-borne fungus Fusarium oxysporum Schlechtend.:Fr. f. sp. niveum (E.F. Sm.) W.C. Snyder & H.N. Hans (Fon). Fon race 1 is most prevalent throughout the U.S. while race 2 is more virulent. Our overall objective is to identify and utilize different germplasm sources and gene loci (alleles) associated with resistance to Fon races 1 and 2 and incorporate the resistance alleles into the genome of watermelon cultivars. Here, we present the use of genotyping-by-sequencing (GBS) technology to construct a single nucleotide polymorphism (SNP)-based genetic map with an F2:3 population derived from closely related parental lines of the cultivated type watermelon Citrullus lanatus and segregating for Fon race 1 resistance. We identified a major quantitative trait loci (QTL) with a 6.1 cM interval on chromosome 1 that explained 59.9% of the variation in resistance to Fon race 1 and six minor QTL. We also used GBS to generate the first Citrullus amarus intra-variety genetic map (previously known as C. lanatus var. citroides collected in southern Africa). Here we used an F2:3 population (N=173) segregating for Fon race 2 resistance. A total of 2,495 binned SNPs formed 11 linkage groups with an average distance of 0.7 centiMorgans (cM) between SNPs and a total map length of 1,798.9 cM. One major and four minor QTL explained 69.3% of the variation in resistance. The major QTL was delimited to a 1.2 Mb interval of chromosome 9, with one putative disease resistance gene. We have subsequently used a QTL-seq approach to increase QTL resolution and develop “kompetitive allele specific polymerase chain reaction (KASP)” markers useful in breeding programs to enhance resistance to Fusarium wilt in watermelon.