Twenty-nine recently introduced diploid (2n = 2x = 20) accessions of section Arachis plus an A. correntina (Burk) Krap. et Greg. norm. nud. control were hybridized to the diploid A-genome spe cies -I. duranwnsis Krap. etGreg. nom. nud. (ace. 7988), the diploid B-genome species .1. batizocoi Krap. et Greg. (acc. 9484), and with two subspecies of the A-B genome (2n = 4x = 40) .1. hypogaea cultivars NC 4 and Argentine. Most attempted crosses were successful and the resulting plants were vigorous.

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... owever, A. hatizocoi x accesrion 30008 hybrids died as seedlings and A.bhaizocoi x accession 30017 produced only dwarf plants. The 710 diploid Fs from .-1. batizocoi were generally sterile, while those from .,. duranensishad fertility ranges from 5% to 84%. Meiotic chromosome relationships in diploid crosses were cytologically eval uated in 185 plants plus tester accessions. Most taxa in section Arachis have an A genome, only A. batizocoi accessions have a B genome, a D genome is represented by accessions 30091 and 30099, anC two other genomic groups, represented by accessions 30011 and 30033, may be present in the section. Most cytological differentiation was found among species originally collect:d in southern and eastern Bolivia. On the other hand, species collected at the extremes of the distribution of section .. lrachis speci.s (northern Argentina to north-central Brazil) were cytologically very similar. Evidence is presented for speciation in Arachis being associated with both genetic diflerentiation and with translocated chromosomes. All taxa in the section except the D-genome species are believed to b,: cross-compatible with .,A.hypogaea. so germplasm introgression from most Arachts species should be possible. the cultivated peanut, A. hypogaea L. (2n = 4x = 40), is a member of the group. Other species of this section will hybridize with A. hvpogaea (Smartt and Gregory, 1967; Gregory and Gregory, 1979; Pompeu, 1983), and the taxonomic '