Date of Award

5-2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Plant and Environmental Science

Advisor

Hassell, Richard L

Committee Member

Adelberg , Jeff

Abstract

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.

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