Genetic Regulation of Development in Sorghum bicolor: II. Effect of the ma(3) Allele Mimicked by GA(3).

The class III, ma(3) (R)-containing maturity genotypes of Sorghum bicolor (L.) Moench differ from all of the other maturity genotypes in that they flower earlier, exhibit rapid shoot elongation sooner after floral differentiation, and exhibit several morphological differences. In the present study, a class III, ma(3) (R)-containing genotype (44M) was compared to two other genotypes (60M, 80M) that differed only at the third maturity locus. GA(3) treatment caused 60M and 80M to undergo floral differentiation earlier, to exhibit an increase in shoot elongation rate sooner after floral initiation, and to exhibit morphological changes including: increased leaf blade and leaf sheath length, decreased leaf width and leaf area, as well as increased dry weight, especially in the culm weight. Since every major morphological character which is different in class III genotypes was changed by GA(3) treatment of the class II genotypes (60M, 80M), thereby causing them to be more like the class III genotypes, it is clear that application of GA(3) makes maturity genotypes with Ma(3) or ma(3) behave as if they contained ma(3) (R). All of these results support the hypothesis that the ma(3) (R) allele increases gibberellin activity in the maturity genotypes with that allele.