Cytokinin autonomy in tissue cultures of phaseolus: a genotype-specific and heritable trait

Intra- and interspecific differences in cytokinin requirement were detected in callus cultures of Phaseolus vulgaris L. and P. lunatus L. Of the ten genotypes of P. vulgaris tested in the present study, one required cytokinin for callus growth, six exhibited some to moderate growth on cytokinin-free medium, and the remaining three grew uniformly in the absence of cytokinin. In contrast, six of the P. lunatus genotypes were strictly cytokinin-dependent, while four genotypes displayed irregular amount of callus growth on cytokinin-free medium. The genotype-specific behavior of Phaseolus callus tissues was independent of the tissue of origin and the time in culture. The inheritance of the cytokinin requirement of Phaseolus tissue cultures was studied in hybrid tissues resulting from crosses between a strictly cytokinin-dependent genotype (P.I. 200960) and two independent genotypes (cv. G 50 and P.I. 286303) of P. vulgaris. Fresh weights of hybrid tissues on cytokinin-free medium were intermediate between and significantly different from the parental tissues. No differences were found between reciprocal hybrids. These results suggest that cytokinin autonomy in tissue cultures of P. vulgaris is a genetic trait under nuclear control. Both parental and intermediate phenotypes were recovered in the F(2) progeny. The frequency distribution of cytokinin-dependent progeny in F(2) and backcross populations indicates that the cytokinin requirement of P. vulgaris callus tissue may be regulated by one set of alleles.