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-fa mily 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 r esponse of the different families within genotypes to GA(3) were not r elated to the leaf length of their untreated seedlings. It is suggeste d that, under given environmental conditions, background genotypic eff ects, inducing inter-family variation in responsiveness to GA(3), regu late the elongation growth up to the limits set by the Rht alleles.