Mapping Alternaria cucumerina resistance in Cucumis melo
J. D. DALEY (1), R. L. Hassell (2), W. P. Wechter (3). (1) Clemson Univeristy, Charleston, SC, U.S.A.; (2) Clemson University, Charleston, SC, U.S.A.; (3) U.S. Vegetable Laboratory, USDA ARS, Charleston, SC, U.S.A.
Alternaria Leaf Blight caused by <i>Alternaria cucumerina</i> is a serious disease affecting worldwide production of melon (<i>Cucumis melo</i>). The resistance gene <i>Ac</i> has been reported in USDA breeding line MR-1, but molecular markers have yet to be identified. Utilizing bulked segregant analysis, we are conducting marker discovery using recombinant inbred lines (RILs) from an initial cross of MR-1 (resistant) and Ananas Yokneam (susceptible) with randomly amplified polymorphic DNA (RAPD) and High Frequency Oligonucleotides-Targeting Active Genes (HFO-TAG) primers. RAPD and HFO-TAG analysis was performed using agarose gel electrophoresis. In addition, a modified HFO-TAG analysis was performed on a genetic analysis system which provided single base pair resolution. Identified polymorphisms are being used to construct a linkage map, which will have immediate utility in marker identification of gene loci associated with <i>Alternaria</i> resistance, as well as other resistance genes found in MR-1. Additionally, in order to increase control and consistency of <i>Alternaria</i> resistance phenotyping, we are developing an improved leaf assay adapted to melon. Leaves were inoculated with a range of concentrations of conidia and incubated under varying conditions (light, temperature, humidity) to determine the optimal method for phenotyping.
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