RESUMO
Blast, caused by Pyricularia oryzae, has become a devastating disease on wheat in several countries worldwide. Growers need alternative methods for blast management, and silicon (Si) stands out for its potential to decrease the intensity of important diseases in several crops. This study investigated the effect of Si on improving photoassimilate production on flag leaves of wheat plants and their partitioning to spikes in a scenario where blast symptoms decreased as a result of potentiation of defense mechanisms by Si. Wheat plants (cultivar BRS Guamirim) were grown in hydroponic culture with 0 or 2 mM Si and inoculated with P. oryzae at 10 days after anthesis. The Si concentration on flag leaves and spikes of Si-supplied plants increased and resulted in lower blast symptoms. High concentrations of total soluble phenols and lignin-thioglycolic acid derivatives and greater peroxidase, polyphenoloxidase, phenylalanine ammonia-lyase, ß-1,3-glucanase, and chitinase activity occurred on flag leaves and spikes of Si-supplied plants and increased their resistance to blast. The concentration of photosynthetic pigments decreased and the photosynthetic performance of infected flag leaves and spikes from plants not supplied with Si was impaired for chlorophyll a fluorescence parameters including maximal photosystem II quantum efficiency, fraction of energy absorbed used in photochemistry, quantum yield of nonregulated energy dissipation, and quantum yield of regulated energy dissipation. The concentration of soluble sugars was lower on infected flag leaves and spikes from plants not supplied with Si, whereas the hexose-to-sucrose ratio increased on infected flag leaves. Sucrose-phosphate synthase activity was lower and acid invertase activity was higher on flag leaves and spikes of plants not supplied with Si, respectively, compared with Si-supplied plants. The starch concentration on spikes of Si-supplied plants increased. In conclusion, Si showed a beneficial effect in improving the source-sink relationship of infected flag leaves and spikes by preserving alterations in assimilate production and partitioning during the grain filling process.
