Karyotypic studies in Solanum section Lasiocarpa (Solanaceae)

Mitotic chromosomes of 13 species included in Solanum sect. Lasiocarpa were studied. All species have 2n = 24. The chromosome numbers of S. stagnale, S. felinum, and S. repandum are reported for the first time. Statistical analyses of chromosomes, genome length, and centromere position yielded estimates of karyotype composition and asymmetry. A generalized karyotype of the section shows that most of the chromosomes are metacentric (73%) or submetacentric (25.6%). Two pairs of subtelocentric chromosomes are present only in S. sessiliflorum. Satellites are quite common, characterizing chromosomes for ten species and are attached to the short arms of either m or sm chromosomes. They could be seen in 10% to 70% of the cells. Only S. pseudolulo bears two satellited chromosomes, one of them attached to a long chromosome arm. Although the section is chromosomally quite homogeneous, species can be distinguished by karyotype formula, presence of satellites in a particular chromosome pair, and total chromosome length. There are no indications of major chromosomal rearrangements within the section. Using cytological data exclusively, cluster analysis indicates S. sessiliflorum is isolated in the section. Solanum candidum and S. vestissimum are somewhat isolated as well and have unique karyological traits. Solanum pectinatum has a peculiar karyotype, but in the phenogram it is not particularly separated. Karyotype features suggest that morphological differentiation was not always followed by chromosomal divergence. The origin of the domesticated S. quitoense is no further elucidated by our data.