Chromosome evolution in Solanum traced by cross-species BAC-FISH.

Chromosomal rearrangements are relatively rare evolutionary events and can be used as markers to study karyotype evolution. This research aims to use such rearrangements to study chromosome evolution in Solanum. Chromosomal rearrangements between Solanum crops and several related wild species were investigated using tomato and potato bacterial artificial chromosomes (BACs) in a multicolour fluorescent in situ hybridization (FISH). The BACs selected are evenly distributed over seven chromosomal arms containing inversions described in previous studies. The presence/absence of these inversions among the studied Solanum species were determined and the order of the BAC-FISH signals was used to construct phylogenetic trees. Compared with earlier studies, data from this study provide support for the current grouping of species into different sections within Solanum; however, there are a few notable exceptions, such as the tree positions of S.similar to etuberosum (closer to the tomato group than to the potato group) and S.similar to lycopersicoides (sister to S.similar to pennellii). These apparent contradictions might be explained by interspecific hybridization events and/or incomplete lineage sorting. This cross-species BAC painting technique provides unique information on genome organization, evolution and phylogenetic relationships in a wide variety of species. Such information is very helpful for introgressive breeding.