POLYMORPHISM OF THE LEGHEMOGLOBIN GENE IN PHASEOLUS DEMONSTRATED BY POLYMERASE CHAIN-REACTION AMPLIFICATION

Genetic variance within Phaseolus vulgaris or among Phaseolus species for leghemoglobin composition may be useful in breeding for enhanced n itrogen fixation. Using primers constructed from conserved regions of the leghemoglobin gene, polymerase chain reaction was used to specific ally amplify the Lba gene in total DNA samples from 17 lines and 10 sp ecies of Phaseolus. These primers are 100% homologous with the 5'- and 3'-ends of the leghemoglobin-encoding genes Lba of Phaseolus vulgaris , Lbc2 and Lbc3 of Glycine max, and 90% homologous to the G. max Lba g ene. With one exception, only a single band was amplified using this a pproach with DNA isolated from 11 species of Phaseolus. The species of Phaseolus used in these experiments can be grouped into six classes b ased on the size of the amplified product which corresponded to their presumed genetic relatedness. Arranged in decreasing order by size the se classes are: (1) Phaseolus lunatus and Phaseolus polystacius, (2) P haseolus anisotrichus; (3) Phaseolus acutifolius, Phaseolus filiformis , Phaseolus angustissimus acc. # 16, and Phaseolus oligospermus; (4) P haseolus angustissimus acc. # 166, which had two major bands; (5) Phas eoluspolyanthus, Phaseolus microspermus, and Phaseolus coccineus; and (6) Phaseolus vulgaris. No significant heterogeneity of amplified prod uct within Phaseolus vulgaris was observed among 12 lines examined, bu t heterogeneity was observed between lines within Phaseolus acutifoliu s and Phaseolus angustissimus. Polymerase chain reaction amplification of conserved genes may be a useful method to facilitate the introgres sion of desirable genes from wild and exotic germplasm.