Does maintaining green leaf area in sorghum improve yield under drought? II. Dry matter production and yield

Retention of green leaf area at maturity (GLAM), known as stay-green, is us ed as an indicator of postanthesis drought resistance in sorghum [Sorghum b icolor (L.) Moench] breeding programs in the USA and Australia. The critica l issue is whether maintaining green leaves under postanthesis drought incr eases grain yield in stay-green compared with senescent hybrids. Field stud ies were undertaken in northeastern Australia on a cracking and self-mulchi ng gay clay. Nine closely related hybrids varying in rate of leaf senescenc e 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 tvas correlated positiv ely with GLAM (r = 0.75**) and negatively with rate of leaf senescence (r = -0.74**). Grain yield also increased by approximate to 0.35 Mg ha(-1) for every day that onset of leaf senescence was delayed beyond 76 DAE in the wa ter-limited treatments. Stay-green hybrids produced 47% more postanthesis b iomass than their senescent counterparts (920 vs. 624 g m(-2)) under the te rminal water deficit regime. No differences in grain yield were found among eight of the nine hybrids under fully irrigated conditions, suggesting tha t 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.