Characterization of diploid, tetraploid and hexaploid Helianthus species by chromosome banding and FISH with 45S rDNA probe.

Comparative karyotype analyses of five diploid, two tetraploid, and three hexaploid species of Helianthus were performed using Feulgen staining, Giemsa C and CMA3 (C-CMA) staining, and FISH with 45S rDNA probe. The karyotypes are composed by a basic number of x = 17 with a predominance of meta- and submetacentric chromosome types. A polyploid series is associated with the basic number. Giemsa C- and C-CMA banding revealed terminal or interstitial heterochromatin according to the species, suggesting the existence of a mechanism that may be acting in the dispersion of heterochromatic segments in Helianthus. The nucleolar organizer regions were located at terminal chromosome positions by FISH with 45S rDNA probe. Diploid species presented four, six, and eight rDNA sites, tetraploid species showed eight sites and hexaploid species presented 12 rDNA sites. Karyomorphological differences include variation in number, size and chromosome morphology, suggesting that rearrangements involving small heterochromatic and rDNA segments played a major role in karyotype evolution.