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Title: Mapping resistance to alternaria cucumerina in cucumis melo

item DALEY, JAMES - Clemson University
item Branham, Sandra
item Levi, Amnon
item HASSELL, RICHARD - Clemson University
item Wechter, William - Pat

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2016
Publication Date: 6/16/2017
Citation: Daley, J., Branham, S., Levi, A., Hassell, R., Wechter, W.P. 2017. Mapping resistance to alternaria cucumerina in cucumis melo. Phytopathology. 107(4):427-432.

Interpretive Summary: Numerous cucurbit crops are severely damaged by Alternaria leaf blight, a fungal pathogen that can decimate a crop. Many of the current cantaloupe cultivars grown in the U.S. are quite susceptible to this disease. While chemical pesticides are routinely used to address Alternaria on cantaloupes, there is a desire by growers and consumers for cantaloupes produced with less pesticides. The breeding line MR-1, developed by the U.S. Vegetable Laboratory, Charleston, SC, possesses numerous resistance genes to a variety of pathogens, and it has high levels of resistance to the Alternaria leaf blight pathogen. ARS scientists at Charleston identified two molecular markers linked to resistance in MR1. These markers will be extremely useful for breeders when using MR1 to incorporate Alternaria leaf blight resistance into new cantaloupe cultivars.

Technical Abstract: Infection with Alternaria cucumerina causes Alternaria leaf blight (ALB), a disease characterized by lesion formation on leaves, leading to substantial yield and quality losses in Cucumis melo (melon). While fungicides are effective against ALB, reduction in the frequency of application would be economically and environmentally beneficial. Resistant melon lines have been identified but the genetic basis of this resistance has not been determined. A saturated melon genetic map was constructed with markers developed through genotyping-by sequencing of an MR-1 (resistant) by Ananas Yokneum (susceptible Israeli cultivar) recombinant inbred line (RIL) population (F6-F10; N=82). The population was evaluated for A. cucumerina resistance with an augmented block greenhouse study using inoculation with the wounded-leaf method. Multiple quantitative trait loci (QTL) mapping identified two QTL that explained 33.9% of variation in lesion area. Several candidate genes within range of these QTL were identified using the C. melo v3.5 genome. Markers linked to these QTL will be used to accelerate efforts to breed melon cultivars resistant to ALB.