Temperature and Photoperiod Effects Mediated by the Sorghum Maturity Genes

Abstract

A more complete understanding of the role of photoperiod and temperature in the genetic control of flowering in sorghum (Sorghum bicolor L. Moench) will allow breeders greater flexibility in making crosses among widely differing maturity types and will also contribute to the understanding of regional adaptation requirements. The objective of this study was to characterize the photoperiodic responses of 10 sorghum lines with all known combinations of the sorghum maturity genes Ma1, Ma2, and Ma3. Twenty growth chamber trials were conducted to examine photoperiods between 11 and 15 h at 0.5‐h intervals and to examine the influence of mean daily temperature as well as the range of day/night temperature. Compared with other genotypes, the recessive maR3 allele resulted in a reduction of 3.1 leaves in the basic vegetative phase (BVP‐Ieaf number under favorable photoperiods) and also eliminated photoperiod sensitivity. There was little influence of Ma2 or Ma3 genes on BVP. The dominant Ma1 allele conferred increased photoperiod sensitivity (4.5 leaves/h) compared to homozygous ma1, condition (1.4 leaves/h). There were no significant differences detected in the Maximum Optimal Photoperiod, which was about 12 h. The Ma2 gene was implicated in a photoperiod ✕ temperature interaction, although the exact role was not clear. The dominant allele of Ma3 increased the phyllochron (leaf development rate) by about 0.2 d/leaf. Thus, the developmental response of sorghum to photoperiod and temperature involves the complementation of effects from these maturity genes.