Ak. Borrell et al., Does maintaining green leaf area in sorghum improve yield under drought? II. Dry matter production and yield, CROP SCI, 40(4), 2000, pp. 1037-1048
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.