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Temperature and Photoperiod Effects Mediated by the Sorghum Maturity Genes

Agriculture Canada Res. Stn., Lethbridge, AB, T1J 4B1, Canada
Biology Dep., Univ. of Lethbridge, Lethbridge, AB, T1K 3M4, Canada
Dep. of Soil and Crop Sciences, Texas A&M Univ., College Station, TX 77843-2474

^* Corresponding author.

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 O.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 ma^R₃ 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 x 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.

Received for publication February 27, 1989.