Silicon (Si) plays a pivotal role in the nutritional status of a wide variety of monocot and dicot plant species and helps them, whether directly or indirectly, counteract abiotic and/or biotic stresses. In general, plants with a high root or shoot Si concentration are less prone to pest attack and exhibit enhanced tolerance to abiotic stresses such as drought, low temperature, or metal toxicity. However, the most remarkable effect of Si is the reduction in the intensities of a number of seedborne, soilborne, and foliar diseases in many economically important crops that are caused by biotrophic, hemibiotrophic, and necrotrophic plant pathogens. The reduction in disease symptom expression is due to the effect of Si on some components of host resistance, including incubation period, lesion size, and lesion number. The mechanical barrier formed by the polymerization of Si beneath the cuticle and in the cell walls was the first proposed hypothesis to explain how this element reduced the severity of plant diseases. However, new insights have revealed that many plant species supplied with Si have the phenylpropanoid and terpenoid pathways potentiated and have a faster and stronger transcription of defense genes and higher activities of defense enzymes. Photosynthesis and the antioxidant system are also improved for Si-supplied plants. Although the current understanding of how this overlooked element improves plant reaction against pathogen infections, pest attacks, and abiotic stresses has advanced, the exact mechanism(s) by which it modulates plant physiology through the potentiation of host defense mechanisms still needs further investigation at the genomic, metabolomic, and proteomic levels.

Blast, caused by the fungus Pyricularia oryzae, is a major disease of the wheat crop in the Brazilian Cerrado and represents a potential threat to world wheat production. However, information about the wheat-P. oryzae interaction is still limited. In this work, the activities of the enzymes superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), glutathione-S-transferase (GST), ascorbate peroxidase (APX), glutathione reductase (GR), and glutathione peroxidase (GPX) and the concentrations of superoxide (O₂(-)), hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) as well as the electrolyte leakage (EL) were studied in wheat plants 'BR 18' and 'BRS 229', which are susceptible and partially resistant, respectively, to leaf blast at the vegetative growth stage, during the infection process of P. oryzae. The blast severity in BRS 229 was 50% lower than in BR 18 at 96 h after inoculation (hai). The activities of SOD, POX, APX, and GST increased for both cultivars in the inoculated plants compared with noninoculated plants and the increases were more pronounced for BRS 229 than for BR 18 at 96 hai. The GR and CAT activities only increased in inoculated plants from BRS 229 at 96 hai. For BR 18, the GR activity was not influenced by plant inoculation, and the CAT activity was lower in inoculated plants. The GPX activity only increased in inoculated plants from BR 18 at 48 and 72 hai. The P. oryzae infection increased the O₂(-), H₂O₂, and MDA concentrations and EL. However, the greater increases of the SOD, POX, APX, GST, GR, and CAT activities for BRS 229 compared with BR 18 contributed to the lower O₂(-), H₂O₂, and MDA concentrations and EL verified in the former. These results show that a more efficient antioxidative system in the removal of excess of reactive oxygen species generated during the infection process of P. oryzae limits the cellular damage caused by the fungus, thus contributing to greater wheat resistance to blast.

Blast, caused by Pyricularia oryzae, has become an economically important disease in wheat in Brazil, but little effort has been devoted to understanding the wheat-P. oryzae interaction. This study was intended to determine the effects of P. oryzae infection on the photosynthetic process in wheat plants using a susceptible (BR 18) and a partially resistant cultivar (BRS 229). It was found that the net carbon assimilation rate (A), stomatal conductance (gs), and transpiration rate were dramatically reduced in both cultivars due to P. oryzae infection but to a lesser degree in BRS 229. Photosynthesis was impaired in asymptomatic leaf tissues, indicating that blast severity is not an acceptable indicator for predicting P. oryzae-induced reductions in A. The proportionally larger decreases in A than in gs, in parallel with increases in internal CO2 concentration (Ci), suggest that the lower influx of CO2 into the diseased leaves caused by stomatal closure was not a prominent factor associated with the reduction in A. Additional support for this conclusion comes from the nonsignificant correlation between A and gs, the negative correlation between A and Ci and the positive correlation between blast severity and Ci. Both the maximum rate of carboxylation and the maximum rate of electron transport were dramatically depressed at advanced stages of P. oryzae infection, mainly in BR 18, although the reduction in A was not closely related to the decrease in the electron transport rate. In conclusion, biochemical limitations likely related to the reduced activity of Rubisco, rather than diffusive limitations, were the main factor associated with decreases in A during the infection process of P. oryzae on wheat leaves.

O objetivo do trabalho foi avaliar o efeito de quatro tratamentos de sementes: água (T1), carbendazim + thiram (T2), fipronil + tiofanato metílico + piraclostrobina (T3) e abamectina + thiamethoxam + fludioxonil + mefenoxan + thiabendazole (T4) sobre parâmetros de crescimento de plantas de soja submetidas a dois regimes hídricos (presença e ausência de estresse hídrico) estabelecidos logo após a emergência das plântulas. O experimento foi conduzido em casa de vegetação e campo. Na casa de vegetação, nos tratamentos sem estresse hídrico, foram feitas quatro irrigações por dia e, nos tratamentos com estresse hídrico, foi realizada uma irrigação a cada três dias. Neste ensaio, foi avaliada a estatura de plantas, comprimento radicular, volume radicular, massa seca da parte aérea, massa seca radicular e área foliar. No ensaio de campo, o estresse hídrico foi estabelecido pela construção de túneis baixos de polietileno que impediram o fornecimento de água pela irrigação e chuva. No campo, foram avaliados estatura de planta, teor relativo de clorofila, emergência, ataque de lagarta-elasmo e rendimento de grãos. Nos dois ambientes, as plantas foram mantidas sob estresse até 28 dias após a emergência. Em casa de vegetação, todos os parâmetros foram influenciados pelo tratamento de sementes na presença e ausência de estresse hídrico. No campo, o tratamento com fipronil + tiofanato metílico + piraclostrobina (T3) e abamectina + thiamethoxam + fludioxonil + mefenoxan + thiabendazole (T4) proporcionaram maior estatura de planta e teor relativo de clorofila em ambos os regimes hídricos e maior emergência e rendimento de grãos em plantas sem e com restrição hídrica, respectivamente. Conclui-se que o tratamento de sementes com esses produtos promove alterações benéficas nas plantas, aumentando sua tolerância ao estresse hídrico, com efeito positivo sobre o rendimento de grãos da soja.

Target spot, caused by the fungus Corynespora cassiicola, has become a serious foliar disease in soybean production in the Brazilian Cerrado. Information in the literature regarding the biochemical defence responses of soybean to C. cassiicola infection is rare. Therefore, the objective of this study was to determine the biochemical features associated with soybean resistance to target spot. The activities of chitinases (CHI), b-1-3-glucanases (GLU), phenylalanine ammonia-lyases (PAL), peroxidases (POX), polyphenol oxidases (PPO) and lipoxygenases (LOX), as well as the concentrations of total soluble phenolics (TSP) and lignin-thioglycolic acid (LTGA) derivatives, were determined in soybean leaves from both a resistant (FUNDACEP 59) and a susceptible (TMG 132) cultivar. The target spot severity, number of lesions per cm 2 of leaflet and area under the disease progress curve were significantly lower for plants from cv. FUNDA-CEP 59 compared to plants from cv. TMG 132. The GLU, CHI, PAL, POX and PPO activities and the concentration of LTGA derivatives increased significantly, whereas LOX activity decreased significantly on the leaves infected by C. cassiicola. Inoculated plants from cv. FUNDACEP 59 showed a higher PPO activity and concentrations of TSP and LTGA derivatives at 4 and 6 days after inoculation compared to plants from cv. TMG 132. In conclusion, the results of this study demonstrated that the defence-related enzyme activities increased upon C. cassiicola infection, regardless of the basal level of resistance of the cultivar studied. The increases in PPO activity and concentrations of TSP and LTGA derivatives, but lower LOX activity, at early stages of C. cassiicola infection were highly associated with soybean resistance to target spot.