Arachis Genetic Resources for Peanut Improvement.

The genus Arachis contains about 80 species, of which many are diploid but tetraploid and aneuploid species have also been described.  The genus has been divided into 9 sections and the cultivated species, A. hypogaea, is an allotetraploid in section Arachis, the largest section with about 31 distinct species.  Most species of section Arachis possess an A genome, with only a few having a B and one with a D genome. Section Arachis species are cross-compatible with A. hypogaea whereas species from the other sections do not hybridize easily with it.  Also, several diploid species in section Arachis have been identified as sources of resistance to many common diseases of peanut and as a result species from this section have received more attention from peanut researchers.  Thus, it is important to study their taxonomic relationship to A. hypogaea in order to develop efficient gene introgression pathways.  In our research program, we have employed conventional cytogenetic approaches combined with molecular marker systems to gain insight into the genomic identities and species relationships in section Arachis.  Many of the newly named Arachis species have been hybridized to representative A and B genome testers and the cytogenetic analysis of the hybrids grouped the species into corresponding A and B genome types.  Molecular analysis indicated some discrepancies. Results from these studies will be discussed with their implication for peanut improvement.