VARIATION IN CHROMOSOMAL DNA ASSOCIATED WITH THE EVOLUTION OF ARACHISSPECIES

The 2C nuclear DNA amounts were determined for 99 accessions, represen ting 23 Arachis species from 8 of 9 taxonomic sections, and two synthe tic amphidiploids. Mean 2C DNA amounts varied by 15.20%, ranging from 10.26 to 11.82 pg, between accessions of Arachis hypogaea (2n=4x=40). Nuclear DNA content variation (5.33-5.91 pg) was also detected among A rachis duranensis (2n=2x=20) accessions. The intraspecific variation i n the two species may have resulted from indirect selection for favour able genome sizes in particular environmental conditions. The accessio ns belonging to A. hypogaea ssp. hypogaea (mean value 11.27 pg) with l onger life cycle had significantly larger mean DNA content than the ac cessions of A. hypogaea ssp. fastigiata (mean value 10.97 pg). For 20 diploid (2n=2x=20) species of the genus, 2C nuclear DNA amounts ranged from approximately 3 to 7 pg. The diploid perennial species of sectio n Arachis have about 12% more DNA than the annual species. Comparisons of DNA amounts show that evolutionary rating is not a reliable guide to DNA amounts in generic sections of the genus; lower DNA values with evolutionary advancement were found in sections Heteranthae and Trise minatae, but the same was not true for sections Arachis and Caulorrhiz ae. Similarly, there is evidence of significant differences in DNA con tent between 4 ancient sections (Procumbentes, Erectoides, Rhizomatosa e, and Extranervosae) of the genus. The occurrence of genome size plas ticity in both A. duranensis and A. hypogaea provides evidence that A. duranensis could be one of the diploid progenitors of A. hypogaea. Th e DNA content in the two synthetic amphidiploids corresponded to the s um value estimated for parental species.