amarus was described as early as 1962 in PI 189225 (Sowell and Pointer 1962) and later in PI 271778 (Sowell 1975 Norton 1979). Citrullus germplasm sources with various levels of host resistance against GSB have been described (Sowell and Pointer 1962 Sowell 1975 Norton 1979 Gusmini et al. 1994 Guner 2005 Thies and Levi 2007 Tetteh et al. 2017) has been a major source of disease resistance alleles in watermelon breeding (Boyhan et al. lanatus) (Chomicki and Renner 2015 Renner et al. 2017), the Citrullus amarus, a wild relative of watermelon ( C. The best alternative would be to utilize GSB-resistant cultivars, but currently commercial watermelon cultivars with high levels of genetic resistance to GSB have not been developed.ĭue to the narrow genetic base of cultivated watermelon following domestication (Guo et al. In addition, fungicide applications greatly increase production costs and their repeated use may have a negative impact on the environment, particularly if residues persist in the soil. However, recent reports of differential fungicide resistance among the three causal Stagonosporopsis species presents a significant challenge to growers since the species cannot be differentiated based on symptoms (Brewer et al. Due to the limited effectiveness of cultural practices on their own, fungicides remain critical for successful management of GSB (Stevenson et al. 2015).Ĭurrent management of GSB in watermelon includes cultural practices and fungicide application. Although morphologically similar, the three Stagonosporopsis species can be distinguished using polymerase chain reaction-based microsatellite markers (Brewer et al. 2010), but it has since been established that the disease is caused by three Stagonosporopsis species: S. Stagonosporopsis cucurbitacearum) (Aveskamp et al. GSB was formerly thought to be caused by a single pathogen: Didymella bryoniae (syn. 1995 Robinson and Decker-Walters 1997 Keinath 2011 Babu et al. The occurrence of GSB is intensified by warm and humid environments that are conducive for germination of the spores and disease development (Keinath et al. It has been reported to infect at least 12 genera and 23 species of Cucurbitaceae, including watermelon ( Citrullus lanatus), cucumber ( Cucumis sativus), cantaloupe and muskmelon ( Cucumis melo), squash ( Cucurbita pepo), and several different genera of gourds (Keinath 2011). Gummy stem blight (GSB) is a devastating fungal disease affecting cultivation of cucurbitaceous vegetable crops worldwide, leading to severe yield losses (Sherbakoff 1917 Chiu and Walker 1949 Sherf and MacNab 1986 Keinath 2011 Stewart et al. Our findings will facilitate the use of molecular markers for efficient introgression of the resistance loci and development of GSB-resistant watermelon cultivars. High throughput markers were developed for selection of ClGSB5.1 and ClGSB7.1. Among them is ClCG07G013230, encoding an Avr9/Cf-9 rapidly elicited disease resistance protein, which contains a non-synonymous point mutation in the DUF761 domain that was significantly associated with GSB resistance. Locus ClGSB7.1 accounted for the highest phenotypic variation and harbors twenty-two candidate genes associated with disease resistance. The genes underlying ClGSB5.1 includes an NBS-LRR gene ( ClCG05G019540) previously identified as a candidate gene for GSB resistance in watermelon. We identified three QTLs ( ClGSB3.1, ClGSB5.1 and ClGSB7.1) associated with GSB resistance, explaining between 6.4 and 21.1% of the phenotypic variation. The population was phenotyped by inoculating seedlings with Stagonosporopsis citrulli 12178A in the greenhouse in two separate experiments, each with three replications. lanatus) and GSB-resistant PI 482276 ( C. The objective of this study was to identify quantitative trait loci (QTLs) associated with GSB resistance in an F 2:3 interspecific Citrullus mapping population ( N = 178), derived from a cross between Crimson Sweet ( C. Utilizing GSB-resistant cultivars would reduce yield losses, decrease the high cost of disease control, and diminish hazards resulting from frequent fungicide application. Currently, no commercial cultivars with genetic resistance to GSB in the field have been reported. Gummy stem blight (GSB), caused by three Stagonosporopsis spp., is a devastating fungal disease of watermelon ( Citrullus lanatus) and other cucurbits that can lead to severe yield losses.
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