INTROGRESSION OF PHASEOLUS-ACUTIFOLIUS-A GRAY GENES INTO THE PHASEOLUS-VULGARIS L GENOME

The tepary bean (Phaseolus acutifolius A. Gray) is a desirable genetic resource for incorporation of improved disease, pest, and stress resi stance into common bean (P. vulgaris L.). Reproductive barriers separa te the two species and the degree to which tepary genes may be introgr essed into the common bean genome has not been well described. Greenho use studies of gene introgression through recurrent backcrossing to co mmon bean were performed using two first backcross (BC1) and nine seco nd backcross (BC2) populations. The truncate primary leaf characterist ic of tepary bean was readily observed but the short primary leaf peti ole and narrow bract tepary traits were infrequently observed in both BC1 and BC2 populations. In one BC1 population high frequencies of ada xial stomata (characteristic of P. acutifolius) and the presence of a 30 kD cotyledon polypeptide from P. acutifolius were also observed; ho wever, a diaphorase isozyme from P. acutifolius appeared to be elimina ted from BC1 progeny at a high rate whereas 6-phosphogluconate dehydro genase alleles appeared to be transmitted normally. The expression of tepary primary leaf truncate morphology and bract width were correlate d with decreased fertility in one of the two BC1 populations. Given su itable parental genotypes and population sizes it should be possible t o transfer genes from P. acutifolius to P. vulgaris, especially in reg ions of the genome which are not associated with inviability or steril ity. It will be difficult to transfer factors from certain regions of the tepary genome which are preferentially eliminated during introgres sion.