Genetic Regulation of Development in Sorghum bicolar: I. Role of the Maturity Genes.

The photoperiodic behavior and other developmental and morphological differences of 11 maturity genotypes (as identified by JR Quinby 1967, Adv Agron 19: 267-305) of the milo group of Sorghum bicolor (L.) Moench were studied under 8, 10, 12, and 14 hour photoperiods. Sorghum is a quantitative short day plant. The genotypes studied differ in genes which modify photoperiodic behavior and thus maturity; the alleles are designated as Ma(1), ma(1), Ma(2), ma(2), Ma(3), ma(3), and ma(3) (R) (single symbols indicate homozygosity at the indicated gene loci). Based on floral initiation (differentiation) under 10, 12, and 14 hour photoperiods the 11 genotypes were assigned to three clases: (I) flower initiation delayed by 12 hour photoperiods (all genotypes with Ma(1)Ma(2) but not ma(3) (R)), (II) flower initiation delayed by 14 hour photoperiods (all genotypes with Ma(1)ma(2), ma(1)Ma(2), or ma(1)ma(2) but not ma(3) (R)), (III) flower initiation not drastically delayed by 14 hour photoperiods (all genotypes with ma(3) (R)). All of the class III genotypes were taller, had longer leaf sheaths, narrower and longer leaf blades, and less leaf area, than the other genotypes. In addition, the class III genotypes initiated rapid culm and thus internode elongation sooner after floral initiation than any of the class I or II genotypes. Dry weight did not differ between the class III genotypes and the others. The rate of leaf emergence in the class III genotypes and all others was indistinguishable until after floral initiation in the former. The allelic combination unique to class I, Ma(1)Ma(2), makes plants very photoperiod sensitive without causing observable changes in morphology or other development events. The allelic combination unique to class III, ma(3) (R), makes plants relatively photoperiod insensitive and results in several differences in morphology and development.