Fabrício Ávila Rodrigues

Foliar spray of potassium silicate on the control of angular leaf spot on beans.

This study aimed to determine if potassium silicate (KSi) sprays could reduce the intensity of angular leaf spot. In field experiment 1, bean plants were sprayed with KSi (pH 10.5) at rates of 8, 20, 40, and 60 g L−1. In field experiment 2, with the same treatments, the pH of the KSi solutions was 5.5. In experiment 3, the treatments were KSi (40 g L−1, pH 5.5), potassium hydroxide (KOH) (6.5 g L−1, pH 5.5), tebuconazole (0.5 L ha−1), and control. In experiment 4, the treatments were the same as in experiment 3, but the pH of the KSi and KOH solutions was 10.5. Plants sprayed with water served as a control treatment for all field experiments. Plants were artificially inoculated with Pseudocercopora griseola before products application. For experiments 3 and 4, the treatment with KOH was included to equalize the amount of potassium (K) with the treatment corresponding to the application of KSi. Disease severity was evaluated using a scale with values ranging from 0.2 to 30.4% at 85 days after seedling emergence. Plant defoliation, Si, and K concentration in the plant tissues, and yield were also determined. There was no relationship between KSi rates and Si concentration in leaf tissues, but Si concentration increased by 58 and 57%, respectively, as the KSi rates increased from 0 to 60 g L−1 regardless of the pH. The K concentration in leaf tissues did not change among the treatments. Disease severity decreased by 42 and 30%, respectively, at the highest KSi rate with pH 5.5 and pH 10.5 over the control. Disease severity levels were similar between the KSi and KOH treatments, but they were significantly higher compared to the tebuconazole. Plant defoliation at the highest KSi rate with pH 5.5 and 10.5 was 17 and 33%, respectively, less than the control. Plant defoliation decreased with the application of KSi with pH 5.5 and 10.5 in 29 and 34%, respectively, compared to the control. Yield increased by 30 and 43%, respectively, as the KSi rates increased from 0 to 60 g L−1with pH 5.5 and 10.5. No statistical difference in yield was detected between the KSi and KOH treatments regardless of the pH used, but both were different from tebuconazole. Significant differences in yield were found only between tebuconazole and the control. Results from this study suggest that foliar application of KSi and KOH has the potential to reduce angular leaf spot severity. The KSi did not offer any advantage over the KOH spray, suggesting a lack of a direct effect of Si accumulated in the leaf tissue on disease control.

Silicon reduces brown spot severity and grain discoloration on several rice genotypes

This study aimed to investigate the effect of silicon (Si) on the reduction of brown spot severity (BSS), caused by Bipolaris oryzae, and grain discoloration in several rice genotypes. An experiment was conducted in a greenhouse where eight genotypes were evaluated for their response to Si rates and decrease on BSS. The relationship between Si rates and BSS was linear negative. Additionally, a field experiment was conducted including forty-eight genotypes which were grown in upland conditions and evaluated for their response to Si rates and reduction on grain discoloration. The relationship between Si rates and grain discoloration was quadratic negative. Weight of filled grains per panicle increased as the Si rates in the soil increased. Genotypic differences for Si concentration in husk were evident for both non-amended and Si-amended plots. While the Si concentration in husk increased to all genotypes, there was no relationship between grain discoloration and Si concentration in husk for plants from non-amended and Si-amended plots. The genotype CAN-7024 with the highest resistance to leaf brown spot also showed the lowest grain discoloration in comparison to the genotypes Casado and Caqui.

Silicon reduces bacterial speck development on tomato leaves

This study aimed to evaluate the effect of silicon (Si) on the resistance of tomato plants (cv. Santa Clara) to bacterial speck, caused by Pseudomonas syringae pv. tomato (Pst). Tomatoes were grown in soil without calcium silicate (control), in soil without calcium silicate and sprayed with Supa Silica® (2 mL/L) (SS) and in soil with calcium silicate (0.16 g/kg of soil) (CS). The effect of SS on the growth of Pst was evaluated in vitro. There was no significant difference among the treatments for foliar Si concentration and incubation period. No significant differences were observed between the control and CS for the number of lesions per plant (NLP) and bacterial speck severity estimated by the software QUANT. The NLP was significantly reduced with SS spray. There was a negative linear response of in vitro Pst growth to the SS rates. Peroxidase, polyphenoloxidase and glucanase activities were significantly higher for plants sprayed with SS and grown in soil with CS compared to the control treatment. Phenylalanine ammonia-lyase and lypoxygenase activities were significantly higher for plants grown in soil with CS compared to the control. The concentration of malondialdehyde was significantly higher for plants sprayed with SS compared to the control at 0 and 7 dai. The results of this study indicate that the symptoms of bacterial speck are reduced when plants are sprayed with SS, which can be linked to the direct effect of this product against Pst rather than the potentation of host defense responses.

Silicon and manganese on the activity of enzymes involved in rice resistance against brown spot

This study investigated the role of silicon (Si) and manganese (Mn) rates on the activity of peroxidases (POX), polyphenoloxidases (PPO) and phenylalanine ammonia-lyases (PAL) on rice plants non-inoculated and inoculated with Bipolaris orzyae. Rice plants (cultivar Metica 1) were grown in nutrient solution with 0 (-Si) or 2 mmol Si L-1 (+Si) and with 0.5, 2.5 and 10 μmol Mn L-1. Plants were inoculated with B. oryzae and leaf samples were collected at 6, 12, 18, 24, 36 and 48 h after inoculation (hai). Leaf samples were also collected from non-inoculated plants at these same time-points. POX activity increased for -Si plants inoculated with B. oryzae at both rates of 0.5 and 2.5 µmol Mn L-1 with one peak at 48 hai at 10 µmol Mn L-1. For plants supplied with Si, POX activity also increased, but seemed to be low at the rates of 2.5 and 10 µmol Mn L-1. POX activity did not show to be greatly influenced by the Mn rates in the presence of Si. However, in the absence of Si, POX activity increased. PPO activity on -Si plants increased at the rate of 0.5 µmol Mn L-1 and was not affected by the other two Mn rates, except a peak at 18 hai at the rate of 10 µmol Mn L-1. In the presence of Si, PPO activity increased on plants supplied with 2.5 µmol Mn L-1 in contrast to the other two Mn rates for which the PPO activity decreased. By comparing the -Si and +Si treatments at the rate of 2.5 µmol Mn L-1, PPO activity increased from 18 to 36 hai in the presence of Si than on its absence. PAL activity on -Si plants decreased regardless of the Mn rates. On plants supplied with Si and inoculated with B. oryzae, PAL showed low activity at the highest Mn rate and also at the rate of 0.5 µmol Mn L-1, besides its activity been very low compared to the non-inoculated plants. PAL did not increase in activity in the presence of Si, but on its absence, high levels of activity were achieved. Results from this study showed that the activities of POX, PPO and PAL were not boosted by Si at any Mn rate.

Resistência física de bainhas de plantas de arroz supridas com silício e infectadas por Rhizoctonia solani

Physical resistance of leaf sheaths of rice plants supplied with silicon and infected by Rhizoctonia solani This study aimed to associate the silicon (Si) deposition on sheaths of rice plants with an increase in physical resistance against infection by Rhizoctonia solani. Plants from the susceptible cultivars BR-Irga 409 and Labelle were grown in nutrient solution containing (+Si) or not (-Si) Si. Si concentration on sheaths of plants supplied with Si and inoculated with R. solani significantly increased compared to plants non-supplied with Si, reducing the relative lesion length at 96 hours after inoculation (hai). There were significant differences between -Si and +Si treatments for the force required of a metal needle to pass through the sheaths at 48 and 72 hai. The greater physical resistance at 24 hai was due to the fact that R. solani was growing on sheath tissue without destroying it, which could be proved by the absence of symptoms. After this period, the resistance decreased due to the rapid R. solani growth. However, on sheaths of plants supplied with Si, the force required for the needle to penetrate was higher at 48 and 72 hai. The sheath resistance of plants supplied with Si to infection by R. solani can be explained partly by the greater physical resistance due to Si deposition.

Componentes epidemiológicos da ferrugem do cafeeiro afetados pela aplicação foliar de silicato de potássio

Epidemiological components of coffee rust affected by foliar application of potassium silicate Leaf rust, caused by Hemileia vastatrix, is the most important coffee disease. Alternative methods of management of this disease that are less damaging to the environment than fungicide applications are urgently needed. This study aimed at evaluating the effect of foliar applications of potassium silicate (PS) solutions at concentrations of 0, 8, 20, 40, and 60 g/L, at pHs 5.5 and 10.5, on sporulation intensity of H. vastatrix (SI), total number of pustules (TNP) per leaf, and on coffee leaf rust severity. The effect of the applications of PS at the selected rates, of copper oxychloride (7.5 g/L), and of sterile distilled water at pH 5.5, 7.5, and 10.5 on the inhibition of H. vastatrix uredospores germination was also tested and the foliar concentration of silicon (Si) and potassium (K) was determined. A quadratic regression model best described the effect of PS applications, at pH 5.5 or 10.5, on SI, TNP, and severity. The relationship between SI, TNP, or severity and PS applications, at pH 5.5 or 10.5, was linear and negative. Si concentration in leaves increased as the concentration of PS solutions utilized (at pH 5.5) increased from 0 to 60 g/L. There was no effect of PS applications, at pH 10.5, on Si concentration in leaves. K concentration did not change as the PS rates increased from 0 to 60 g/L, both at pHs 5.5 and 10.5. A linear regression model adequately described the relationship of inhibition of uredospores germination versus PS concentrations at the three pHs values. Copper oxychloride significantly reduced uredospore germination as compared with the PS applications. The results from this study highlight the possibility of using PS spray, in a more alkaline pH, as a treatment for reducing coffee leaf rust intensity.