Plant Genome III Conference Plant Genome III Conference
Two ripe fruit diseases of tomato, blackmold (Alternaria alternata) and watermold (Pythium ultimum), can cause significant yield losses of processing tomatoes. The F2 and F3 generations of a cross between a susceptible Lycopersicon esculentum cultivar VF 145B-7879 and the resistant wild relative L.cheesmanii f. typicum accession LA422 were used to identify QTL that were associated with resistance to these two diseases. Classical inheritance studies revealed that resistance to both diseases is quantitative. F3 families were used to reconstructed the F2 generation to map QTL for resistance. 120 RFLPs were used to construct a map with markers spaced 10-20 cM across the entire genome. Analysis of variance at each marker and Mapmaker/QTL were used to determine the position of the putative QTL. Both methods gave similar results. Four QTL were associated with resistance to blackmold, but the mm QTL were not identified in both the F2 and F3 generations probably reflecting the low heritability and high environmental variation of this trait. Six QTL were associated with resistance to watermold and two of these regions were identified in both the F2 and F3 generations. Genes for resistance to both blackmold and watermold were contributed from both parents. This population was also segregating for fruit size and leaflet number. Five QTL were identified that were associated with leaflet number in the F2 generation and three of these QTL were also detected in the F3 generation. Four QTL for leaflet number correspond to the position of genes for mutant leaf phenotypes on the classical tomato map. Four QTL were identified for fruit diameter in the F2 generation and two of these QTL were also found in the F3 generation.