INTROGRESSION OF AGRONOMIC CHARACTERS FROM EXOTIC COWPEA GERMPLASM INTO BLACKEYE BEAN

Genetic diversity of blackeye bean germplasm (Vigna unguiculata (L.) Walp.) adapted to irrigated environments is limited. Introgression of exotic germplasm may be necessary for future improvement of agronomic characteristics, but methods for its efficient utilization are not well established. The present study investigated how different sources of exotic germplasm and different proportions of exotic and adapted germplasm affect trait means, genetic variability, and frequency of agronomically acceptable lines. Twenty-eight random lines from each of two adapted- x -exotic crosses were evaluated at each of three levels of introgression (F2:4, BC1F3, and BC2F2). These six combinations and the adapted recurrent parent were grown in a replicated experiment at Davis, CA, and evaluated for seed yield, seed size, harvest index, and days to first flower. The recurrent parent was 'California Blackeye No. 5'. The exotic donor parents (Bush 2 and Bush 5) were of tropical African origin. Seed yields of F2:4, BC1F3, and BC2F2 populations were 68%, 85% and 88%, respectively, of the recurrent parent mean for the Bush 2 population; and 68%, 71%, and 82%, respectively, of the recurrent parent mean for the Bush 5 population. BC2F2 populations derived from Bush 2 and Bush 5 retained 67% and 54% of the genetic variability for seed yield exhibited by their respective F2:4 populations. Genetic variance estimates for most traits were comparable between populations derived from either Bush 2 or Bush 5. Means and range of expression for seed yield were greater for the populations derived from Bush 2. Backcross populations generally had greater genetic variance than would be expected if only additive gene action is assumed and dominance of factors in the exotic lines could partially explain this result. Only the BC2F2 populations had any lines with acceptable expression of both seed yield and seed size. Backcross populations were judged to be a superior source of breeding lines with immediate usefulness compared to their single-cross counterparts.