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Gibberellins and Heterosis in Sorghum

Dep. of Biological Sciences Univ. of Lethbridge, Lethbridge, AB T1K 3M4, Canada

David J. Major and Fred R. Miller

Crop Science Section, Agric. Canada Res. Stn., Lethbridge, AB T1J 4B1 Canada
Dep. of Soil and Crop Sciences, Texas A&M Univ., College Station, TX 77843

^* Corresponding author.

Two triplet combinatioas of sorghum, [Sorghum bicolor (L.) Moench], each consisting of two homozygous parental lines and their F₁ hybrid (ATx623 x Hegaria; ATx378 x RTx430), were grown in controlled environment chambers to examine the possible relationship between gibberellins (GAs) and heterosis (hybrid vigor). Heterosis for shoot growth occurred as shoot dry weights and leaf areas were greater in the hybrids than in parental inbreds. The exogenous application of 0.1, 0.5, or 1.0 mg GA₃ by pipetting into the leaf whorl promoted leaf sheath and leaf blade elongation in all genotypes. GA₃ also promoted shoot dry weight and/or leaf area in three of the four inbreds, but hybrids were relatively unaffected. Endogenous GA₁ was measured by gas chromatography-selected ion monitoring, using [²H₂]GA₁ as an internal standard. At one of the two harvests (Day 22 and 29) for each triplet, the hybrid contained significantly higher concentrations of GA₁ than either parent. Endogenous GA₃ was characterized by GC-SIM in samples, from the second harvest and showed the same pattern as GA₁. Thus, at some stages, these sorghum inbreds apparently have a partial deficiency of endogenous GA. The response to exogenous GA₃ application suggests that the GA deficiency is a limitation to their growth. Thus, GAs are apparently involved in heterosis for shoot growth in sorghum.

Received for publication March 6, 1991.