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Sinchieh Liu and Martha A. Mutschler

The transfer of multigenic traits into tomato has been slow due to interspecific barriers (hybrid breakdown) found in the F2 of the Lycopersicon esculentum × L. pennellii cross (esc × pen), including blocks in normal reproductive development and nonfecundity. In a typical (esc × pen) F2 population, failure to flower and premeiotic blocks in pollen development occurred in 2% and 11% of the population, respectively. The remaining plants showed a mean of 37% stainable pollen. Twenty three percent of the F2 plants set seed, with an average of 4.5 seeds/fruit. An average of 33% of the stainable pollen from the 7 F2 plants with the highest stainable pollen measurements germinated in vitro, but only 4 of these 7 plants set seed. Thus, percent stainable pollen is not an adequate predictor of fecundity, and the non-fecundity in the F2Le plants must involve barriers occurring after pollen germination.

A method was developed which greatly reduces or eliminates each of the F2 barriers. The method and its efficacy on each of the aspects of hybrid breakdown will be discussed.

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Martha A. Mutschler, Rebecca W. Doerge, Sin-Chieh Liu, Jian P. Kuai, Barbara E. Liedl, and Joseph A. Shapiro

Lycopersicon pennellii, a wild relative of the tomato, L. esculentum, is resistant to a number of important pests of cultivated tomato due to the accumulation of acylsugars, which constitute 90% of L. pennellii LA716 type IV trichome exudate. An interspecific F2 population created by crossing L. esculentum × L. pennellii was surveyed for acylsugar accumulation and subjected to RFLP analysis to determine the genomic regions associated with the levels of acylglucoses, acylsucroses, and total acylsugars accumulated, and glucose as a percentage of total acylsugars. Data was analyzed using MAPMAKER with and without log10 transformation and using a threshold of either 2.4 (default value for MAPMAKER) or ones calculated according to the Permutation-based Estimated Threshold (PET) method. Genomic regions were identified for each of the traits studied. Effects of analytical method on identification of QTLs, similarities between these results and results published for the genus Solanum, and similarities between these results and the regions transferred by a breeding program selecting for acylsugar production are discussed.