The contribution of ear photosynthesis to grain filling in bread wheat (Triticum aestivum L.)

The contribution of ear photosynthesis to grain filling in wheat (Triticum aestivum L) is not well known. The main objective of this work was to evaluate this contribution through three different experimental approaches: (1) ear photosynthesis was reduced by removing awns or shading the ears (in combination with a defoliation treatment), (2) grain weight per ear was compared in an 'all shaded' crop versus plants where only the vegetative parts were shaded ('ear emerging'), and (3) ear photosynthesis was reduced with DCMU (3-(3,4-dichloropheny1)-1,1-dimethylurea), a specific inhibitor of photosystem II. In field experiments in La Plata (Argentina), cultivars Klein Escudo and BioINTA 3000 were subjected to awn removal and ear shading treatments, with or without severe defoliation, and to 'all canopy shaded' versus 'ear emerging' treatments. Although the estimated contribution of ear photosynthesis to grain yield differed depending on the experimental approach used (from about 12-42%), in general cv. Klein Escudo (with the largest awns) showed a greater contribution of ear photosynthesis. In both cultivars, the percentage contribution of ear photosynthesis was larger for defoliated plants. The magnitude of this contribution was positively associated with the length of awns of each cultivar. Awn removal had a nonsignificant (p <= 0.05) effect on grain weight per ear (GW(ear)) in the short-awned cv. BioINTA 3000. In cv. Klein Escudo, the effects of de-awning were larger, reaching values of ca. 15 and 19% decrease of GW(ear) in non-defoliated and defoliated plants respectively. In both cultivars, grains in a distal position within the spikelet (G3) were most affected by the decrease of the photosynthetic source. The photosynthetic rate of the ear was higher in cv. Klein Escudo than in cv. BioINTA 3000. We analyzed the contribution of remobilization of pre anthesis assimilates (stem plus sheaths). Comparing both cultivars, dry matter translocation from the stem showed the opposite pattern to the contribution of ear photosynthesis, i.e. it was higher in cv. BioINTA 3000 than in Klein Escudo. In Bordenave, Argentina, ear shading treatments revealed an important contribution of ear photosynthesis to grain yield in cv. Huenpan (a long awned, water-deficit tolerant genotype), either under water deficit or irrigation, whereas in cv. Baguette Premiun 11 (short awns) there was apparently no effect of ear photosynthesis on yield. Finally, inhibition of ear photosynthesis with DCMU reduced grain weight per ear to a similar extent as ear shading. Ear photosynthesis might represent a "buffer" to maintain grain yield under source limitations (e.g. defoliation, water stress conditions), and could have an important role even without stress, because an incipient 'source' limitation might be emerging in modern cultivars of bread wheat. (C) 2010 Elsevier B.V. All rights reserved.