Files
Abstract
Watermelon production is hindered by biotic and abiotic stresses that are intensified by long production cycles. Flowering time is a determining factor in early fruit production for growers, which results in reduced production costs and increased profitability. This study aimed to develop high-throughput molecular markers useful for selection of the early flowering trait to enable acceleration of cultivar development and improve diploid-triploid pairing in seedless watermelon breeding. Using QTL-seq and KASP assays, the flowering time locus was refined from a 5 Mb region to ~1.13 Mb region on chromosome 3. UGA3_10795402, UGA3_15424397 and NW0248748 were identified as markers appropriate for selection of flowering time depending on the genetic background. Diseases are another major challenge for growers in the Southeast due to the hot, humid weather that is conducive for plant disease development. Gummy stem blight caused by three Stagonosporopsis spp. is one of the most important diseases of watermelon and currently no resistant cultivars are available to growers. The three causal species exhibit differential sensitivity to fungicides, making disease management difficult. This work aimed to establish if the three species have similar host responses, as it remains unclear whether differential host resistance is partially responsible for the lack of success in resistance breeding efforts. The effect of various Stagonosporopsis isolates on different Citrullus genotypes was evaluated and it was noted that isolate aggressiveness was not species dependent. In addition, some wild relatives of watermelon exhibited broad resistance to Stagonosporopsis isolates. Due to the lack of genetic resistance to GSB in commercial watermelon, we sought to identify chromosomal regions associated with this trait, with a future goal of resistance introgression into the commercial varieties. An interspecific population developed from a cross between a susceptible Crimson Sweet and resistant PI 482276 was used to map GSB resistance. Loci associated with GSB resistance were identified on chromosomes 3 (ClGSB3.1), 5 (ClGSB5.1) and 7 (ClGSB7.1) of watermelon, with the latter explaining up to 21% of the phenotypic variation. High throughput molecular markers including ClGSB5.1-1, ClGSB7.1-1 and ClGSB7.1-2 were developed for utility in MAS of GSB resistance in watermelon breeding.