Does Maintaining Green Leaf Area in Sorghum Improve Yield under Drought? II. Dry Matter Production and Yield

Abstract

Retention of green leaf area at maturity (GLAM), known as stay‐green, is used as an indicator of postanthesis drought resistance in sorghum [ Sorghum bicolor (L.) Moench] breeding programs in the USA and Australia. The critical issue is whether maintaining green leaves under postanthesis drought increases grain yield in stay‐green compared with senescent hybrids. Field studies were undertaken in northeastern Australia on a cracking and self‐mulching gray clay. Nine closely related hybrids varying in rate of leaf senescence were grown under two water‐limiting regimes, post‐flowering water deficit and terminal (pre‐ and postflowering) water deficit, and a fully irrigated control. Under terminal water deficit, grain yield was correlated positively with and negatively with rate of leaf senescence Grain yield also increased by ≈0.35 Mg ha −1 for every day that onset of leaf senescence was delayed beyond 76 DAE in the water‐limited treatments. Stay‐green hybrids produced 47% more postanthesis biomass than their senescent counterparts (920 vs. 624 g m −2 ) under the terminal water deficit regime. No differences in grain yield were found among eight of the nine hybrids under fully irrigated conditions, suggesting that the stay‐green trait did not constrain yield in the well‐watered control. The results indicate that sorghum hybrids possessing the stay‐green trait have a significant yield advantage under postanthesis drought compared with hybrids not possessing this trait.