Foliar application of silicon decreases wheat blast symptoms without impairing photosynthesis

ABSTRACT Considering the importance of blast, caused by Pyricularia oryzae, to impact wheat yield, this study investigated whether the foliar spray of potassium silicate (PS) could affect the photosynthesis of wheat plants and its potential to reduce disease symptoms. The Exp. 1 aimed to determine the effect of the foliar spray of PS on the photosynthetic performance of plants and was arranged in a completely randomized design with six treatments (plants sprayed with PS rates of 2.5, 5.0, 7.5, 10.0, and 12.5 g·L-1 at 35 days after emergence) and six replications. The leaf gas exchange (net CO2 assimilation rate (A), internal CO2 concentration (Ci), stomatal conductance to water vapor (gs), and transpiration rate (E)) as well as fluorescence of chlorophyll a (maximal photosystem II quantum yield (Fv/Fm), quantum yield of non-regulated energy dissipation [Y(NO)], photochemical yield [Y(II)], electron transport rate (ETR), and quenching non-photochemical [Y(NPQ)]) parameters were evaluated. The Exp. 2 was carried out to determine the effect of PS on blast control and also on the photosynthetic performance of plants. Plants at 35 days after emergence were sprayed with PS rate of 12.5 g·L-1, which did not affect photosynthesis on plants from Exp.1. This experiment was a 2 × 4 factorial and arranged in a completely randomized design with six replications. The factors studied were plants non-inoculated or inoculated plants and the spray of water, PS, fungicide (trifloxystrobin 10% + tebuconazole 20%; 0.75 L/ha), and fungicide + PS. There were no significant changes in the values of A, gs, E, Ci, Fv/Fm, Y(NO), Y(II), Y(NPQ), and ETR for plants sprayed three times (every 96 h interval) as the PS rates increased from 2.5 to 12.5 g·L-1. There was no significant relationship between the PS rates with either absorbance, reflectance or transmittance on the leaf blades. Linear regression model best described the foliar Si concentration-PS rates relationship. Foliar Si concentration significantly increased by 44 and 42%, respectively, for the PS and PS + fungicide treatments compared to water-sprayed plants. The area under disease progress curve was significantly lower by 64, 58, and 53%, respectively, for the fungicide, PS, and fungicide + PS treatments in comparison to water-sprayed plants. The photosynthetical process, primarily related to the Fv/Fm parameter, on wheat leaves was greatly impaired during the infection process of P. oryzae, but to a lesser extent on the leaves of PS-sprayed plants. In conclusion, the foliar spray of PS can be an environmentally friendly strategy to control wheat blast without causing perturbation to the photosynthetic machinery of wheat plants.

摘要 鉴于稻梨孢菌（Pyricularia oryzae）引发的稻瘟病对小麦产量的显著影响，本研究旨在探讨硅酸钾（potassium silicate, PS）叶面喷施对小麦植株光合性能的影响，及其减轻病害症状的应用潜力。试验1旨在明确硅酸钾叶面喷施对植株光合性能的影响，采用完全随机设计，设置6个处理（于出苗后35天喷施浓度为2.5、5.0、7.5、10.0及12.5 g·L⁻¹的硅酸钾溶液），并设置6次重复。测定指标包括叶片气体交换参数：净CO₂同化速率（A）、胞间CO₂浓度（Cᵢ）、水汽气孔导度（gₛ）及蒸腾速率（E），以及叶绿素a荧光参数：光系统II最大量子产额（Fv/Fm）、非调节性能量耗散量子产额[Y(NO)]、光化学量子产额[Y(II)]、电子传递速率（ETR）及非光化学猝灭[Y(NPQ)]。
试验2旨在探究硅酸钾对小麦稻瘟病的防控效果及植株光合性能的影响。于出苗后35天喷施浓度为12.5 g·L⁻¹的硅酸钾溶液（该浓度在试验1中未对植株光合性能产生负面影响）。本试验为2×4析因设计，采用完全随机设计，设置6次重复，研究因素包括：未接种与接种稻梨孢菌的植株，以及喷施清水、硅酸钾、杀菌剂（肟菌酯10% + 戊唑醇20%；施用量0.75 L/ha）、杀菌剂+硅酸钾4种处理。
当硅酸钾喷施浓度从2.5 g·L⁻¹提升至12.5 g·L⁻¹时，连续喷施3次（间隔96 h）的植株，其A、gₛ、E、Cᵢ、Fv/Fm、Y(NO)、Y(II)、Y(NPQ)及ETR值均无显著变化。小麦叶片的吸光度、反射率及透射率与硅酸钾喷施浓度均无显著相关性。叶片硅含量与硅酸钾喷施浓度的关系以线性回归模型拟合效果最优。与喷施清水的对照组相比，硅酸钾及硅酸钾+杀菌剂处理的植株叶片硅含量分别显著提升44%和42%。
与喷施清水的对照组相比，杀菌剂、硅酸钾及硅酸钾+杀菌剂处理的病情进展曲线下面积分别显著降低64%、58%和53%。在稻梨孢菌侵染过程中，小麦叶片的光合过程（主要与Fv/Fm参数相关）受到显著抑制，但硅酸钾喷施处理的植株叶片受影响程度较轻。综上，硅酸钾叶面喷施可作为一种环境友好型的小麦稻瘟病防控策略，且不会干扰小麦植株的光合机构。