Recombinant inbred lines for genetic mapping in tomato

A cross between the cultivated tomato Lycopersicon esculentum and a related wild species L. cheesmanii yielded 97 recombinant inbred lines (RILs) which were used to construct a genetic map consisting of 132 molecular markers. Significant deviation from the expected 1:1 ratio between the two homozygous classes was found in 73% of the markers. In 98% of the deviating markers, L. esculentum alleles were present in greater frequency than the L. cheesmanii alleles. For most of the markers with skewed segregation, the direction of the deviation was maintained from F2 to F7 generations. The average heterozygosity in the population was 15%. This value is significantly greater than the 1.5% heterozygosity expected for RILs in the F7 generation. On average, recombination between linked markers was twice as high in the RILs than in the F2 population used to derive them. The utility of RILs for the mapping of qualitative and quantitative traits is discussed.