Silicon‐Induced Changes in the Antioxidant System Reduce Soybean Resistance to Frogeye Leaf Spot

Abstract

Frogeye leaf spot (FLS), caused by the fungus Cercospora sojina, is one of the most important soybean diseases and can cause great yield losses. Several studies have demonstrated that silicon (Si) enhances the plant antioxidant system, especially when they are subjected to stresses. Thus, this study was designed to evaluate the effect of Si on soybean resistance to FLS, on the antioxidant system, on the concentration of reactive oxygen species and on cellular damage during the infection process of C. sojina. Plants from cultivars Bossier and Conquista, susceptible and resistant to FLS, respectively, were supplied with either 0 (−Si) or 2 mm (+Si) and non‐inoculated or inoculated with C. sojina. FLS severity was greater for Bossier than for Conquista, regardless of the Si supply, and it was increased by Si for both cultivars. The activities of the most antioxidant enzymes were lower in the +Si plants than in the −Si plants when they were not inoculated. Inoculated plants usually showed an increased enzyme activities and higher concentrations of ascorbate and reduced glutathione than did the non‐inoculated plants, regardless of Si supply. At advanced stages of fungal infection, the +Si‐inoculated plants from Bossier had higher activity of most antioxidant enzymes and higher concentrations of superoxide and malondialdehyde compared to the non‐inoculated plants as a result of an increased oxidative stress. The results from this study provide the first evidence that Si reduces the basal activity of antioxidant enzymes in soybean leaves leading to an increase in host susceptibility to FLS.

Changes in leaf gas exchange and chlorophyll a fluorescence on soybean plants supplied with silicon and infected by Cercospora sojina

“…The present results not only bring support to the concept soybean susceptibility to frogeye spot can be potentiated by Si (Nascimento et al., , ), but also provide the first evidences at the physiological and biochemical levels. The susceptibility of soybean plants to frogeye spot potentiated by Si was linked to a reduction on their photosynthetic performance, especially for those of the most susceptible cultivar.…”

“…In agreement with these results, tomato plants infected by Botrytis cinerea showed reduced chlorophylls concentration (Kuźniak & Skłodowska, ). This decrease, similarly reported in the present study, was linked to an increase in the concentration of ROS in the leaflets of soybean plants supplied with Si and infected by C. sojina (Nascimento et al., ).…”

“…By contrast, Nascimento et al. (, ) noticed an increase in the susceptibility of soybean plants to FLS when supplied with Si. Deshmukh et al.…”

“…However, considering that one of the effects of Si on the resistance of plants against pathogens infection is on the increase on H 2 O 2 concentration (Shetty et al., ; Sun et al., ) and photorespiratory process (Van Bockhaven, De Vleesschauwer, & Höfte, ), which also increase the H 2 O 2 levels, it is believed that the infection by C. sojina had benefited itself by the high ROS generated at the infection sites that culminated to a great impairment of the photosynthetic apparatus as previously reported by Nascimento et al. ().…”

“…Potassium silicate was passed through a cation‐exchange resin (Amberlite IR‐120B, H + form; Sigma‐Aldrich, São Paulo, Brazil) to obtain the monosilicic acid (Ma, Tamai, Ichii, & Wu, ). The Si concentration of 2 mM (+Si) was used to prepare the nutrient solution (Debona et al., ; Nascimento et al., , ) to allow the highest Si uptake by plants during their growth.…”