Open Access

When optimizing pre-anthesis dry matter (DM) partitioning among plant organs to enhance grains per m2 and harvest index, the consequences for post-anthesis photosynthetic capacity should be considered. Key processes to consider are: i) leaf lamina and leaf sheath DM partitioning in relation to light interception and photosynthetic rate; ii) non-structural (water soluble carbohydrates; WSC) stem DM partitioning in relation to utilization of stored assimilate for grain filling; and iii) the spike's potential capacity for up-regulation of photosynthesis in relation to decreases in the source:sink balance. In this study, for a set of 26 CIMMYT spring wheat genotypes, grain source:sink balance was estimated by comparing grain weight (GW) responses to several source:sink manipulation treatments. The objectives were to quantify variation in source:sink balance and associations with DM partitioning with photosynthetic traits and grain yield. Results showed responses of cultivars to a de-graining treatment ranged from 1% to 27.9% increases in individual GW in 2011, 2012 and 2013 (P <0.001). The overall decreases in GW in response to a leaf lamina defoliation treatment ranged from -6.5 to -16% (P <0.05) in 2012 and 2013, and in response to a leaf sheath covering treatment from -9.3 to -11.2% (P <0.01) in 2014. Our results indicated that the grain yield of high yielding lines was co-limited by source and sink and that the leaf sheath's contribution to grain filling is important in the studied genotypes and should be taken into account when optimizing partitioning pre-anthesis to enhance HI in high biomass backgrounds.

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