Selectable traits to increase crop photosynthesis and yield of grain crops

Abstract

The grain yield of cereals has almost doubled this century as a result of genetic manipulation by plant breeding. Surprisingly, there has been no change in the rate of photosynthesis per unit leaf area to accompany these increases. However, total photosynthesis has increased as a result of an increase in leaf area, daily duration of photosynthesis or leaf area duration. There remain substantial opportunities to continue to improve total photosynthesis and crop yield genetically using conventional breeding practices. Selectable traits are discussed here in the context of increasing total above-ground biomass under favourable conditions. Opportunities exist to alter crop duration and the timing of crop development to match it better to radiation, temperature and vapour pressure during crop growth, and to increase the rate of development of early leaf area to achieve rapid canopy closure. The importance of these traits will depend on the environment in which the crop is grown. Increases in crop photosynthesis through breeding are also likely to come via indirect means. Selection for a high and sustained stomatal conductance during the period of stem elongation is one way. Increasing assimilate allocation to the reproductive primordia so as to establish a large potential sink should also indirectly increase total crop photosynthesis. Evidence in the major grain crops suggests that by anthesis the capacity for photosynthesis is high and that photosynthesis is not limiting during grain filling. To use this surplus capacity it is suggested that carbon and nitrogen partitioning to the reproductive meristem be increased so as to establish a high potential grain number and the potential for a large grain size. It is then expected that additional photosynthesis will follow, either by a longer daily duration of photosynthesis or by an extended leaf area duration.

Respiration hastens maturation and lowers yield in rice

“…In uncontrolled three-dimensional growth, lacunarity does not exist, unlike in fractal growth patterns. The role of respiration in controlling the size of a plant, not the other way around as conventionally argued in allometry (Reiss, 1989), is consistent with the observations on the enhanced yield in crop plants due to total leaf area/ biomass (Shipley and Vu T-T, 2002) and not photosynthetic efficiency per unit leaf area (Richards, 2000). The replacement of volume (which incorporates the lacunarity) with mass and, respiration as the basis of differential growth dynamics rather than the result of growth, have important consequences in understanding allometric behaviour of plants.…”

Overexpression of a NAC transcription factor delays leaf senescence and increases grain nitrogen concentration in wheat

“…For further improvement of yields to fulfil growing demand, new targets and strategies must be identified. One possible route to increase crop yield is to extend the duration of photosynthesis (Richards 2000). This may be achieved by delaying leaf senescence during grain filling and creating a functional stay‐green phenotype (Thomas & Howarth 2000).…”

Utility of basic research in plant/crop physiology in relation to crop improvement: a review and a personal account

“…Hamblin (1993) discussed the merits and shortcomings of Donald s ideotype concept, particularly when applied to stressful environments. Advances in adopting the ideotype concept for breeding cultivars adapted to various environmental conditions have been demonstrated in cereal crops such as wheat (Sedgely and Belford, 1991;Buxton et al, 1993;Hamblin, 1993;Richards, 2000), rice (Jennings,1964;Chang et al, 1967;Athwal, 1971) and in cassava (Cock et al, 1979;ElSharkawy and Cock, 1987;Cock and El-Sharkawy, 1988;Hershey and Jennings, 1992;Kawano et al, 1998;Jennings and Iglesias, 2002;Kawano, 2003, El-Sharkawy, 2004Kawano and Cock, 2005;Lenis et al, 2006).…”

“…El-Sharkawy conditions. Also, there is evidence that yield enhancement in the semi-dwarf high-yielding wheat cultivars, as compared to tall individuals, may be attributed to both high harvest index coupled with a strong grain sink and high leaf photosynthetic rates (Lupton, 1972;El-Sharkawy, 1975;Ruckenbauer, 1975;Richards, 2000). Moreover, research at the International Maize and Wheat Improvement Center (CIMMYT), Mexico, on assessing the physiological basis underlying yield improvements in semi-dwarf spring wheat cultivars released between 1962 and 1988, revealed some interesting findings (Fischer et al, 1998).…”