Genetic and morphological variability in populations of the wild diploid potato species Solanum maglia and Solanum kurtzianum from Argentina

Solanum maglia Schltdl., a wild potato species that has its widest geographical distribution in Chile, is restricted in Argentina to Quebrada La Cumbre (quebrada = gorge), Mendoza province, where no other potato species has been reported. During two collecting expeditions carried out in 2006 and 2007 in this gorge, tubers of two potato populations separated by 500 m (area 1 and 2) were sampled. The morphological and genetic diversity of these two newly sampled populations and of five accessions from the same gorge classified as S. maglia, a plant of Solanum kurtzianum collected outside this gorge, and a Chilean plant of S. maglia were examined by comparing 24 morphological characters and electrophoretic patterns for simple sequence repeat and amplified fragment length polymorphism markers, respectively. Based on the current taxonomic concept, the results support the classification of plants from area 1 as S. kurtzianum and those from area 2 as S. maglia, except for one plant from the former area, which shared electrophoretic bands from both species. This is the first report on the sympatry of populations of the two species in Quebrada La Cumbre. The importance of performing in situ population studies in the same sites over years is discussed.

Morphological and molecular evidence of natural interspecific hybridization in the diploid potato Solanum kurtzianum from Argentina

The common potato, Solanum tuberosum L. subsp. tuberosum , is a tetrasomic tetraploid. This subspecies has approximately 220 related tuber-bearing species that constitute a genetic pool of enormous breeding value. The diploid species Solanum kurtzianum Bitter et Wittm., described as resistant to drought and nematodes, grows in northwestern and western Argentina and can naturally hybridize with the related diploids Solanum chacoense Bitter, Solanum spegazzinii Bitter, and Solanum maglia Schltdl., in areas of sympatry. In this species, the variability for morphological phenotypes and pollen–pistil relations in intra- and interspecific crosses is large. To investigate whether S. kurtzianum accessions available at the Germplasm Bank in Argentina belong to one taxon with great morphological plasticity or are hybrid and (or) segregant populations, these and accessions of the other three species were characterized using morphological and molecular (SSR) markers. Data were statistically analyzed with ANOVAs and AMOVA. With univariate ANOVA, only 11 characters out of 33 evaluated were statistically significant among species. With multivariate analyses, the grouping did not reflect a priori taxonomic assignments; when population averages were used, a tendency was observed towards grouping by geographical origin. With the AMOVA, only individuals within accessions were separated. Interspecific hybridization and introgression in areas of sympatry can explain these results.

Genomic instability in Solanum tuberosum × Solanum kurtzianum interspecific hybrids

The use of interspecific crosses in breeding is an important strategy in improving the genetic base of the modern cultivated potato, Solanum tuberosum L. Until now, it has normally been interspecific Solanum hybrids that have been morphologically and cytologically characterized. However, little is known about the genomic changes that may occur in the hybrid nucleus owing to the combination of genomes of different origin. We have observed novel AFLP bands in Solanum tuberosum × Solanum kurtzianum diploid hybrids; 40 novel fragments were detected out of 138 AFLP fragments analyzed. No cytological abnormalities were observed in the hybrids; however, we found DNA methylation changes that could be the cause of the observed genomic instabilities. Of 277 MSAP fragments analyzed, 14% showed methylation patterns that differed between the parental species and the hybrids. We also observed frequent methylation changes in the BC1 progeny. Variation patterns among F1 and BC1 plants suggest that some methylation changes occurred at random. The changes observed may have implications for potato breeding as an additional source of variability.Key words: DNA methylation, genome instability, interspecific hybrids, potato, Solanum.