Karyotypic Evolution and Molecular Cytogenetic Analysis of Solanum pinnatisectum, a New Source of Resistance to Late Blight and Colorado Potato Beetle in Potato

Abstract

To efficiently transfer important disease and insect resistance traits from diploid Mexican wild species Solanum pinnatisectum to tetraploid cultivated Solanum tuberosum, molecular cytogenetic and karyotypic analyses were carried out to examine the degree of chromosomal and genomic variation between these 2 species. The results demonstrated that the chromosome complement in S. pinnatisectum was predominantly metacentric and submetacentric, while S. tuberosum showed prominent subtelocentric and telocentric chromosomes. It appears that karyotype evolution from diploid to tetraploid originates through chromosome rearrangements, involving mainly deletions or multiplication at the same ploidy level. Fluorescence in situ hybridization (FISH) using 18S-5.8S-26S ribosomal RNA (rDNA) as a probe demonstrated that both diploid and tetraploid potato species had a single nucleolus organizer region (NOR) locus. However, the localization of the rDNA sites in one of the 2 accessions of S. pinnatisectum was characterized by a pair of morphologically distinct chromosomes, in which one was a submetacentric chromosome, while its homologous partner was a subtelocentric chromosome, which was very similar to that observed in tetraploid potato. This indicated that chromosome variation in structural alterations and nuclear DNA content, as well as loss or addition of highly repetitive sequences could play a role in potato evolution and development of new cultivars. This study offers a useful molecular cytogenetic marker for species identification, chromosome inheritance and potential introgression in future intergenetic hybridization experiments with Mexican wild potato species.