Introgression and DNA marker analysis of Lycopersicon peruvianum, a wild relative of the cultivated tomato, into Lycopersicon esculentum, followed through three successive backcross generations

Segregation of the Lycopersicon peruvianum genome was followed through three generations of backcrossing to the cultivated tomato L. esculentum cv 'E6203' using molecular markers. Thirteen BC1 plants were genotyped with 113 markers, 67 BC2 plants with 84 markers, and finally 241 BC3 plants were genotyped with 177 markers covering the entire genome and a BC3 map constructed. Several segments of the genome, including parts of chromosomes 3, 4, 6, and 10, quickly became fixed for esculentum alleles, possibly due to sterility problems encountered in the BC1. Observed overall heterozygosity and chromosome segment lengths at each generation were very near the expected theoretical values. Markers located near the top telomeric region of chromosome 9 showed segregation highly skewed towards the wild allele through all generations, suggesting the presence of a gamete promoter gene. One markers, TG9, mapped to a new position on chromosome 9, implying an intrachromosomal translocation event. Despite the great genetic distance between the two parents, overall recombination was only 25 % less than that observed in a previous tomato cross, indicating that L. peruvianum genes may be more readily introgressed into cultivated germplasm than originally believed.