Karyological features and banding patterns in Arachis species belonging to the Heteranthae section

The section Heteranthae of Arachis is endemic to Brazil, occurring mainly in the semi-arid northeastern region. The section is considered derived within the genus and includes only annual herbs. Most previous cytological evaluations were restricted to chromosome numbers and morphology. The present approach comprised karyomorphological evaluation in 10 accessions from five species of this section, including standard staining and fluorochrome banding [chromomycin A3 (CMA)/4',6-diamidino-2-phenylindole (DAPI)]. All accessions presented diploid chromosome numbers (2n = 20) with a prevalence of metacentric to submetacentric chromosome morphology. Arachis dardani, Arachis pusilla, and Arachis interrupta presented karyotypic formula 18m + 4sm and satellite type 2, while Arachis sylvestris and Arachis giacomettii presented 16m + 4sm and satellite type 10. Despite the conserved morphological features, higher diversity was detected in terms of size and number of GC-rich (CMA(+)) heterochromatic blocks among the species; however, all of them were located in the pericentromeric regions. The species A. pusilla presented the highest number of GC-rich blocks, present in all chromosomes of the complement. Based on the data obtained and considering literature data, we suggest that A. dardani and A. interrupta occupy a basal position in the group due to their moderate asymmetry and satellite type. At least in A. pusilla, the constitutive heterochromatin seems to have suffered recent modifications of its constitution, in contrast to other species that present pericentromeric CMA(+) blocks in all chromosomes. A. giacomettii and A. sylvestris are closely related to each other and also similar to the previously studied Arachis seridoensis, revealing two clear-cut subgroups within the section from the karyological point of view.