Date of Award
Master of Science (MS)
Plant and Environmental Science
Hassell, Richard L
Adelberg , Jeff
Melon (Cucumis melo L.) production is significantly affected by Alternaria leaf blight, caused by Alternaria cucumerina. Fungicide application is the primary control method; however, this could be mitigated through the increased use of resistant varieties. USDA-ARS breeding line MR-1 has been shown to have a high level of resistance to Alternaria cucumerina. However, molecular markers linked MR-1 Alternaria resistance have yet to be identified. In order in identify QTL associated with Alternaria resistance MR-1 x Ananas Yokneum (AY) derived recombinant inbred lines (RILs) were phenotyped using a modified wounded-leaf assay. Elemental sulfur is an effective fungicide for several foliar pathogens in many crops and species, but severe phytotoxicity prohibits its use on many melon lines. Sulfur tolerance is a heritable trait and QTL have been identified. MR-1 is highly susceptible to sulfur and AY is completely resistant. In order to identify sulfur tolerance QTL, MR-1 x AY RILs were rated for tolerance using vaporized sulfur. A genetic map of MR-1 x AY RILs was constructed using 198 dominant markers (1 SCAR, 24 HFO-TAG, 25 ISSR, and 152 RAPD). This linkage map contains 23 linkage groups and spans 400cM with a maximum marker interval of 10cM and an average marker interval of 2cM. Quantitative trait analysis of 56 RILs for Alternaria resistance and 57 RILs for sulfur tolerance detected three QTL: one Alternaria resistance QTL, ac.1, and two sulfur tolerance QTL, st.1 and st.2. Ac.1 represents the MR-1 resistance allele, is located on linkage group 11, and explains 25% of the variance. St.1 and st.2 were located on linkage groups 1 and 12 and explain 30% and 18% of the variance, respectively. MR-1 allele, st.1, increased susceptibility while the MR-1 allele, st.2, increased tolerance. QTL for these important traits will be beneficial for MAS and genetic studies.
Daley, James, "MAPPING QUANTITATIVE TRAIT LOCI ASSOCIATED WITH ALTERNARIA LEAF BLIGHT RESISTANCE AND ELEMENTAL SULFUR TOLERANCE IN MELON" (2014). All Theses. 1973.