Genotypic Responses to Auxins in Tissue Cultures of Phaseolus

Responses of seven Phaseolus genotypes to the four auxins picloram, 2,4‐D, NAA and 1AA, in tissue cultures, were examined. Callus growth was promoted by picloram and the range of effective concentrations for most genotypes was broad. The auxin 2,4‐D also enhanced callus growth, but the range of optimal concentrations was markedly narrower than that of picloram. NAA when supplied at relatively high concentrations gave good growth. IAA was ineffective in supporting callus growth. The differences in 2,4‐D concentrations required for optimal growth and the differential responses to low concentrations (0.04–1.25 μM) of picloram between several genotypes tested were large. These genotypic variations in auxin responses were repeatable and may thus reflect genetic differences.