Mining Wild Species Alleles From Introgressed Genotypes.

Tomato (Solanum Section Lycopersicon) is composed of one cultivated (S. lycopersicum) and 12 wild species. Because the species are closely related to each other, introgression breeding has been used extensively and released cultivars have been improved for many more traits using wild alleles than has any other crop. Beneficial traits transferred into cultivars from wild species have included disease, pest or abiotic stress tolerance or resistance, ease of mechanical harvesting and fruit quality components. In addition, natural hybridization between S. lycopersicum and its closest wild relative S. pimpinellifolium has been well-documented in sympatric populations. We compared DNA sequences at 47 loci from genotypes of S. lycopersicum and wild tomato species S. pimpinellifolium, Solanum arcanum, Solanum peruvianum, Solanum pennellii and Solanum habrochaites in order to interpret origins of alleles that were apparently introgressed into S. lycopersicum. Cladograms, splits networks, genomic map positions, and historical origins of accessions were used to decipher evolutionary patterns at nine of the 47 loci that showed evidence of introgression. We found that four markers were involved in linkage drag during breeding while alleles at five markers apparently originated from natural hybridization with S. pimpinellifolium. The intrinsic value of naturally introgressed germplasm has been recognized in other crops as a source of novel alleles for various traits. If horticultural effects of introgression are subtle, then accessions descended from interspecific hybridization will be prime sources to screen for new alleles. The positive identification of introgressed genes within tomato will help inform conservation and utilization of germplasm diversity. This includes both facilitating the purging of undesirable linkage drag and the exploitation of novel, favorable alleles.