Abstract
Stay-green sorghum plants exhibit greener leaves and stems during the grain-filling period under water-limited conditions compared with their senescent counterparts, resulting in increased grain yield, grain mass, and lodging resistance. Stay-green has been mapped to a number of key chromosomal regions, including Stg1, Stg2, Stg3, and Stg4, but the functions of these individual quantitative trait loci (QTLs) remain unclear. The objective of this study was to show how positive effects of Stg QTLs on grain yield under drought can be explained as emergent consequences of their effects on temporal and spatial water-use patterns that result from changes in leaf-area dynamics. A set of four Stg near-isogenic lines (NILs) and their recurrent parent were grown in a range of field and semicontrolled experiments in southeast Queensland, Australia. These studies showed that the four Stg QTLs regulate canopy size by: (1) reducing tillering via increased size of lower leaves, (2) constraining the size of the upper leaves; and (3) in some cases, decreasing the number of leaves per culm. In addition, they variously affect leaf anatomy and root growth. The multiple pathways by which Stg QTLs modulate canopy development can result in considerable developmental plasticity. The reduction in canopy size associated with Stg QTLs reduced pre-flowering water demand, thereby increasing water availability during grain filling and, ultimately, grain yield. The generic physiological mechanisms underlying the stay-green trait suggest that similar Stg QTLs could enhance post-anthesis drought adaptation in other major cereals such as maize, wheat, and rice.
Highlights
IntroductionFeeding more people with less water is a major challenge facing humanity (Foley et al, 2011), requiring crops that are highly adapted to dry environments
The stay-green trait is positively correlated with sorghum grain yield in field conditions under terminal drought (Borrell et al, 1999, 2000b; Jordan et al, 2003, 2012)
Establishing this correlation is important because sorghum breeders were initially concerned that leaves may remain green because of a small sink demand, indicating that stay-green may be correlated with low grain yield (Henzell and Gillieron, 1973; Duncan et al, 1981; Rosenow et al, 1983; Tangpremsri, 1989)
Summary
Feeding more people with less water is a major challenge facing humanity (Foley et al, 2011), requiring crops that are highly adapted to dry environments. While the global population will increase from about 7 billion to 9 billion by 2050, most of the increase will occur in sub-Saharan Africa, where population growth is among the highest in the world (Haub, 2013), increasing the risk of food insecurity in this region (United Nations Development Programme, 2012) Plant traits such as semidwarfism and enhanced responsiveness to N fertilizer increased food production in the so-called Green Revolution in the 1960s and 1970s (Khush, 2001). A new set of plant traits is needed to further increase crop yield in a Blue Revolution (Pennisi, 2008), making plants resilient to the challenges of a water-scarce planet where climate change and global warming threaten food supplies (Vidal, 2013)
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