Plant design features that improve grain yield of sorghum under post-anthesis drought stress

Restricting pre-anthesis water use is an important adaptation mechanism to post-anthesis drought stress of sorghum. The aim of this paper was to identify crop physiological processes associated with known differences in drought adaptation among a range of sorghum hybrids. Plants were grown in large containers in five semi-controlled experiments under either well-watered conditions (anthesis harvest) or post-anthesis drought (maturity harvest) and in an irrigated field experiment at two plant densities, all in south-east Queensland. Observations included leaf area dynamics, tillering, transpiration, transpiration efficiency (TE), biomass, and grain yield. Under low plant density, adapted hybrids restricted pre-anthesis plant size, either through early anthesis or reduced tillering. As hybrids did not differ in TE, smaller plant size reduced pre-anthesis water use. This enabled maintenance of grain number and hence grain yield under drought. Reduced tillering was attained likely through vigourous main shoot growth in response to high leaf appearance rate (LAR). However, this mechanism of drought adaptation may be less effective in environments with high temperatures early in the season, where high LAR caused a disproportionate increase in leaf number and genotypic differences in tillering were small. In environments where tillering is suppressed, differences in dry mass partitioning among organs within an axis may be an alternative mechanism to drought adaptation. Linking these crop physiological causes of genotype-by-environment interactions for grain yield under drought to underpinning QTLs could provide useful tools for crop improvement programs to exploit specific adaptation to drought