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CROP PHYSIOLOGY & METABOLISM

Does Maintaining Green Leaf Area in Sorghum Improve Yield under Drought? I. Leaf Growth and Senescence

^a Hermitage Research Station, Department of Primary Industries, Warwick Queensland 4370, Australia
^b QDPI/CSIRO Agricultural Production Systems Research Unit, Toowoomba Queensland 4350, Australia

borrela{at}dpi.qld.gov.au

Production of sorghum [Sorghum bicolor (L.) Moench], an important cereal crop in semiarid regions of the world, is often limited by drought. When water is limiting during the grain-filling period, hybrids possessing the stay-green trait maintain more photosynthetically active leaves than hybrids not possessing this trait. To improve yield under drought, knowledge of the extent of genetic variation in green leaf area retention is required. Field studies were undertaken in northeastern Australia on a cracking and self-mulching gray clay to determine the effects of water regime and hybrid on the components of green leaf area at maturity (GLAM). Nine hybrids varying in stay-green were grown under a fully irrigated control, postflowering water deficit, and terminal (pre- and postflowering) water deficit. Water deficit reduced GLAM by 67% in the terminal drought treatment compared with the fully irrigated control. Under terminal water deficit, hybrids possessing the B35 and KS19 sources of stay-green retained more GLAM (1260 cm² plant^-1) compared with intermediate (780 cm² plant^-1) and senescent (670 cm² plant^-1) hybrids. RQL12 hybrids (KS19 source of stay-green) displayed delayed onset and reduced rate of senescence; A35 hybrids displayed only delayed onset. Visual rating of green leaf retention was highly correlated with measured GLAM, although this procedure is constrained by an inability to distinguish among the functional mechanisms determining the phenotype. Linking functional rather than phenotypic differences to molecular markers may improve the efficiency of selecting for traits such as stay-green.

Abbreviations: APL, area per leaf • CNPP, culm number per plant • DAE, days after emergence • FTN, fertile tiller number • GLAM, green leaf area at maturity • LAI, leaf area index • LAR, leaf appearance rate • ND, no water deficit treatment • PFD, postflowering water deficit treatment • SPLA, senesced plant leaf area • TD, terminal water deficit treatment • TLN, total leaf number on the main culm • TPLA, total plant leaf area • TPLA_max, maximum total plant leaf area • TT, thermal time. *, **, *** Significant at the 0.05, 0.01, and 0.001 probability levels, respectively

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