Karyotype analysis and chromosome evolution in southernmost South American species of Crotalaria (Leguminosae)

Abstract

Karyotypes of 18 populations belonging to eight of the southernmost species of South American Crotalaria were examined. All had x = 8, except C. incana which had x = 7. Diploid, tetraploid and octoploid species were found. The octoploid is a new record and is the highest ploidy level detected so far in the genus. Species within the same ploidy level could be distinguished by quantitative karyotype parameters and by the size and position of the satellites. From an evolutionary point of view, our results support a decrease of the basic chromosome number by dysploidy. Polyploidy is one of the more important mechanisms of chromosome change, even though some structural rearrangements may explain variations of the karyotype formula. Gigas effects, due to polyploidy, were evident in the length of the stomatal guard cells and in pollen size, but were less clear in seed weight. Nucleotype effects, caused by the DNA quantity in a nucleus, were also evident for pollen and stomatal guard cell size and seed weight, although only in diploids with x = 8 for the latter character. Chromosome data are further discussed in the light of the infrageneric systematic arrangement.