CROP WILD RELATIVES

ABSTRACT: Identification of ecogeographic parameters associated with genetic variation would help to prioritize populations within conserved species for collection and maintenance. Previous studies comparing accessions of three Solanum species representing different breeding systems, S. fendleri A. Gray (a disomic polyploid selfer), S. jamesii Torr. (a diploid outcrosser), and S. sucrense Hawkes (a polysomic polyploid outcrosser), revealed no significant associations between genetic and ecogeographic variation. Even physical separation did not predict genetic distance. These previous studies are expanded here by investigating the relationship of genetics and geographic parameters for a fourth type of breeding system: a diploid selfer, modeled by wild S. verrucosum Schlechtd (2n = 2x = 24) from Mexico. The objective was to assess whether genetic distances between accessions are predicted by differences in geographic parameters at the natural sites of origin. Twenty-seven S. verrucosum accessions were studied using 152 RAPD markers to estimate the genetic distance between pairs of accessions. The association of genetic variation with proximity of the S. verrucosum accessions to other Mexican wild potato species (some known to be sympatric with S. verrucosum) was also analyzed. Pairwise comparisons showed that the average GD of all pairs of accessions was 12.8% (ranging from 0–29.3%). Parameters with variation significantly correlated with the average GD of S. verrucosum populations were physical separation (0.42), latitude (0.70), longitude (0.51), proximity to S. hjertingii Hawkes (0.80), S. hougasii Corr. (−0.75), and S. demissum Lindl. (−0.50). Significant effects of proximity to S. hjertingii (for example) might be caused by introgression, or the coincidence that all S. hjertingii occur in the extreme NE corner of the S. verrucosum range.