| One of the largest collections of natural populations of wild tomato species is maintained at the C. M. Rick Tomato Genetics Resource Center (TGRC) at the University of California, Davis. Lycopersicon chilense (syn. Solanum chilense), is a wild relative of cultivated tomato found in N. Chile and S. Peru, and is tolerant to many important diseases and abiotic stresses. Thirty-three accessions of L. chilense were chosen to conduct a diversity analysis, and seven sympatric accessions of the sister species L. peruvianum were included for biological comparisons. These accessions were used to analyze mating system, molecular variation, reproductive isolating barriers, and morphological variation. Strict allogamy, enforced by self-incompatibility, was observed in most populations; however self-compatibility was observed in marginal populations of L. chilense and L. peruvianum. Partitioning of genetic variation within L. chilense indicated significant variation between geographically defined groups, reinforced by the presence of significant isolation by distance. Intraspecific reproductive barriers showed similar spatial patterns of isolation between populations as suggested by the molecular analysis. Three geographically defined groups showed reduced seed set (<50% of normal) in crosses with other accessions: the northernmost accessions ('Acari'), montane accessions from the center of the distribution ('Belen'), and the southernmost coastal accessions ('Taltal'). Reduced seed set observed in crosses between these groups appeared to be due to pre-zygotic barriers. Ten morphological traits were observed for all populations, and morphological distance calculated by cluster analysis. Various distance matrices were compared with each other: geographical, elevational, genetic, crossing, and morphological distances. Significant positive correlations were detected between geographic and both genetic and morphological distances, indicating that genetic and morphological differentiation may be due to genetic drift. Intraspecific reproductive isolation was not correlated with genetic distance, geographic isolation, or variation in mating system. An analysis of quantitative trait loci (QTL) in a cross between L. chilense and cultivated tomato detected up to four QTL for morphological traits used in the diversity study. Despite a high degree of correlation between traits, only two genomic regions affected more than one trait. Taken together, these results suggest that genetic resource evaluation should integrate biological, molecular, and morphological parameters for characterization of natural populations, as different traits provide complimentary information. |
