Gibberellins and Heterosis in Sorghum

Abstract

Two triplet combinatioas of sorghum, [Sorghum bicolor (L.) Moench], each consisting of two homozygous parental lines and their F1 hybrid (ATx623 × Hegaria; ATx378 × 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.