The C.M. Rick Tomato Genetic Resources Center (TGRC) is a genebank of wild relatives, monogenic mutants, and miscellaneous genetic stocks of tomato. The wild species group includes representatives of all nine Lycopersicon spp., as well as four related Solanum species. One of the roles of the TGRC has been to foster the use of the widest available gene pool for tomato researchers. The wild nightshade Solanum lycopersicoides possesses a number of potentially useful traits, but has been untapped by breeders because of sterility and incompatibility barriers. We are using molecular markers to identify alien chromosomal segments introgressed from S. lycopersicoides into tomato. This project involves development of RFLP, RAPD, and isozyme marker linkage maps and their use in selection of homozygous segmental substitutions in backcross inbred progenies. In this fashion, a large proportion of the S. lycopersicoides genome has been integrated into the cultivated tomato. This study has also provided information on the nature of sterility and novel variation in hybrid derivatives.