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.

ABSTRACT Mango wilt, caused by the fungus Ceratocystis fimbriata, is an important disease affecting mango production. In view of the beneficial effects of potassium (K) in other profitable crops and the lack of information about the effect of macronutrients on mango wilt development, the present study aimed to evaluate how mango plants supplied with K respond physiologically when infected by C. fimbriata. Mango plants (» 3 years old) from cultivar Ubá were grown in plastic pots containing 58 mg of K·dm−3 (original K level based on the chemical analysis of the substrate) or in plastic pots with substrate amended with a solution of 0.5 M potassium chloride (KCl) to achieve the rate of 240 mg K·dm−3. Disease symptoms were more pronounced in inoculated plants grown at the lower K level. Substantial declines in stomatal conductance, in line with decreases in the internal-to-ambient CO2 concentration ratio and the absence of detectable changes in the chlorophyll a fluorescence parameters, suggest that the decrease in the net carbon assimilation rate is due, at least initially, to stomatal limitations. High concentrations of K and manganese were found in the stem tissues of inoculated plants and supplied with the highest K rate, most likely due to the involvement of these tissues in the local development of defense mechanisms. The results of this study suggest that the supply of K favored the physiological performance of mango plants and their resistance against C. fimbriata infection.