Sink-limitation to yield and biomass: a summary of some investigations in spring wheat

Abstract

Yield potential can be expressed as a product of light interception, radiation use efficiency (RUE), and the partitioning of biomass to grain yield, or harvest index (HI). Traits related to early or late light interception have not been shown to be associated with genetic improvement of spring wheat yield in favourable environments. It is, however, well established that yield improvement is largely a result of increased HI, although the most recent studies comparing genetic progress in HI over time in spring wheat indicate that it has not made any additional progress since the mid 1980s. These observations suggest that future genetic progress in yield will most likely be achieved by focusing on constraints to RUE. Considering the possibility that RUE may be influenced indirectly by sink limitation, it is apparent that biomass may be increased by increasing grain number, for example. Experiments with high yielding spring wheat lines containing the alien translocation 7DL.7Ag showed increased grains m -2 (15%), yield (12%), and biomass (9%) compared with controls. The translocation was also associated with a larger investment in spike mass at anthesis (15%), more grains/spike (10%), and increased flag-leaf photosynthetic rate during grain-filling (20%). The data suggest that increased biomass in 7DL.7Ag lines was due to significantly increased RUE post-anthesis, as a result of a larger kernel number (sink) that increased the demand for photosynthesis during grain-filling. The hypothesis that increased photosynthesis and RUE may respond directly to a larger number of grains/spike was tested experimentally by imposing a light treatment during boot stage. The treatment was associated with a small increase (5%) in the proportion of biomass invested in spike mass at anthesis, reflected by on average three extra grains/spike at maturity. The treatment was associated with 25% more yield and 22% more biomass than controls, while carbon assimilation rate measured on flag-leaves during grainfilling was 10% higher than controls. The results suggest that RUE can be increased indirectly by increasing sink strength and that the current yield limiting process in spring wheat is the determination of kernel number. Experimental data are presented on how spike fertility may be increased through breeding, for example by introgression of the multi-ovary trait to increase grain number per spikelet. In addition, results of analysis of the physiological bases of genotype × year interaction in high yield environments are presented in the context of how such information can provide a focus for genetic studies of sink limitation.

Wheat physiology: a review of recent developments

“…While low radiation (as simulated by post-anthesis shading) and high temperature can reduce GW by tipping the source-sink balance towards source limitation, in most wheat studies GW is quite insensitive to artificial manipulation of source/sink, such that in the control crop, sink limitation appears to dominate during grain filling (Borras et al 2004;Miralles and Slafer 2007). A component of this apparent insensitivity is seen in the increased P max during grain filling when GN was artificially increased in four modern varieties (Reynolds et al 2005).…”

Effect of drought stress on yield and yield components, relative leaf water content, proline and potassium ion accumulation in different white bean (Phaseolus vulgaris L.) genotype

“…The high harvest index of these two genotypes under stress shows the appropriate and increasing distribution of photosynthesis material towards economical yield and this can be a desirable characteristic in producing high yield plants. Reynolds et al (2005) harvest index in water shortage conditions could be related to adaptation to stress and results in optimized yield in the seed filling phase due to the movement of the stem reserve and an increased capability in water accessibility.…”

Field Measurements of Canopy Spectra for Biomass Assessment of Small-Grain Cereals

“…The relationship between above-ground biomass and yield has been demonstrated empirically in wheat. Positive associations (R 2 =0.56, P<0.05) have been reported between biomass at maturity and yield in durum wheat (Waddington et al, 1987), and between biomass at anthesis and yield in bread wheat (Reynolds et al, 2005;Shearman et al, 2005;Singh et al, 1998;Tanno et al, 1985;Turner, 1997;Van der Boogaard et al, 1996), durum wheat (Royo et al, 2005), barley (Ramos et al, 1985) and rice (Turner, 1982). In a study conducted in Mediterranean conditions with 25 durum wheat cultivars, Villegas et al (2001) found a strong association (R 2 =0.75, P<0.001) of the biomass accumulated from the first node detectable stage with anthesis and yield.…”