Further Cytogenetic Information on Arachis stenosperma (Leguminosae)

Abstract

Arachis stenosperma is a wild relative of the groundnut, with a peculiar disjunct distribution in Central Brazil and along the Atlantic coast. Arachis species show one pair of satellited chromosomes (SAT) and some species have a distinct, smaller pair (A pair). The SAT chromosomes are classified according to 10 types. Previous literature information on A. stenosperma documents the presence of SAT type 3 only in the coastal populations, while type 5 was restricted to accessions from Central Brazil. This work sampled a broader area of geographic distribution, represented by an increased number of accessions, and provides further information on karyotypic characteristics. All 23 accessions analyzed present 2n=20. SAT type 5 was found in 10 accessions, irrespective to their area of occurrence. So, type 5 occurs also in the Atlantic coast. Type 3, so far exclusive to the Litoral, is not the most frequent type in the area. With the present data, the potential cytogenetic distinction between coastal and continental populations has vanished. The formula 18m+2sm clearly predominates, both in the Litoral and in Central Brazilian populations. Also irrespective to the area of origin, both idiogram positions A9/SAT10 and SAT9/A10 were identified. As the SAT of type 3 is considered more primitive than type 5, and the coastal area of distribution of A. stenosperma is secondary, it's future detection in continental populations is expected. In the meantime, a unique cytogenetic feature, the presence of SAT type 3 persists as an exclusive attribute of the populations of the secondary area of occurrence.