GENOTYPIC VARIATION IN THE RESPONSIVENESS TO GA(3) WITHIN TALL (RHT1) AND SEMIDWARF (RHT1) SPRING WHEAT

The effect of GA(3) on coleoptile- and first leaf elongation of tall (rht1) and semi-dwarf (Rht1) nearly-isog enic genotypes, within each of 25 random F-9 wheat families, was determined on seedlings grown in a growth room at 18 degrees C. Conspicuous and very significant inter-family variation in the response of the first leaf to GA(3) application was found in both the rht1 and Rht1 genotypes. The magnitudes of the response of the different families within genotypes to GA(3) were not related to the leaf length of their untreated seedlings. It is suggested that, under given environmental conditions, background genotypic effects, inducing inter-family variation in responsiveness to GA(3), regulate the elongation growth up to the limits set by the Rht alleles.