Silicon potentiates the activities of defense enzymes in the leaf sheaths of rice plants infected by Rhizoctonia solani

Abstract

This study aimed to assess the ability of silicon (Si) to potentiate defense enzyme activities in rice leaf sheaths and thus reduce sheath blight, caused by Rhizoctonia solani, development. Rice plants of BR-Irga 409 and Labelle cultivars were grown in a hydroponic solution containing 0 (-Si) or 2 mM (+Si) Si and inoculated with R. solani. Silicon concentration in the leaf sheaths was significantly higher in the +Si plants than the -Si plants by 727% for BR-Irga 409 and 714% for Labelle. The area under relative lesion expansion progress curve was significantly lower for +Si plants than -Si plants, by 34.2% for BR-Irga 409 and 30.59% for Labelle. Increases in the activities of phenylalanine ammonia-lyases, peroxidases, polyphenoloxidases and chitinases in the leaf sheaths of plants supplied with Si, especially of those from BR-Irga 409, led to reduced progress of sheath blight lesions. Key words: Oryza sativa, fungal disease, host defense response, mineral nutrition, sheath blight.Rice (Oryza sativa L.) is one of the most important carbohydrate sources for the world population, and the occurrence of sheath blight, caused by the necrotrophic fungus Rhizoctonia solani Kühn (teleomorph Thanatephorus cucumeris (A. B. Frank) Donk), has contributed to dramatically decrease yield (Ou, 1985). Severely infected plants produce poorly filled or empty grains, especially those on the lower portion of the panicle (Rush & Lee, 1992). The occurrence of severe sheath blight epidemics and the consequent reduction in yield have been favored by flood irrigation, rotation with soybeans and the use of high-yielding cultivars that are susceptible to the disease (Bedendo & Prabhu, 2005).Sheath blight needs to be managed to prevent yield losses caused by this disease worldwide. Soil amendment with various sources of soluble silicon (Si) has been proposed as an environmentally friendly choice for sheath blight management worldwide (Datnoff et al., 2007). Although Si is not considered an essential nutrient for plants, it is noted for its potential to decrease the intensity of important diseases in several crops, especially grasses (rice, sorghum and wheat) and some dicots (cucumber and soybean) (Datnoff et al., 2007). The increased blast resistance of rice plants when supplied with Si has been attributed to a higher density of long and short silicate cells in the leaf epidermis and/or the existence of a thick silica layer below the cuticle forming a physical barrier that prevents or slows Pyricularia grisea penetration (Kim et al., 2002). Increased concentrations of phenolics, lignins and phytoalexins, enhanced activity of defense-related enzymes (chitinases, β-1,3-glucanases and phenylalanine ammonialyases) and the rapid and strong induction of genes related to host defense against pathogens are the biochemical mechanisms that are potentiated by Si in rice (Rodrigues et al., 2003(Rodrigues et al., , 2004(Rodrigues et al., , 2005Liang et al., 2006;Brunings et al., 2009). This study aimed to determine the effects of Si on the activi...

Silicon induces hormetic dose-response effects on growth and concentrations of chlorophylls, amino acids and sugars in pepper plants during the early developmental stage

“…Importantly, abrasiveness of plant tissues is more influenced by phytolith morphology than by Si concentration applied (Hartley et al, 2015). Moreover, physical strength of the leaf resulting from Si accumulation may induce mechanical protection and thus lower the rate of infection of some pathogens (Zhang et al, 2013;Schurt et al, 2014;Ning et al, 2014). Priming of plant defense responses, alterations in phytohormone homeostasis, and networking by defense signaling components are all potential mechanisms involved in Si-triggered resistance responses (Wang et al, 2017).…”

Silicon, the silver bullet for mitigating biotic and abiotic stress, and improving grain quality, in rice?

“…Sheath blight, Rhizoctonia solani was decreased in two rice cultivars grown hydropically with 2 mM Si compared to no silicon (Schurt et al, 2014). Other studies into the effects of silicon fertilization and infection rates by sheath blight found that enhanced silicon in the shoot protected both a sensitive and insensitive cultivar from this fungus (Zhang et al, 2013 b).…”

The role of silicon (Si) in increasing plant resistance against fungal diseases

“…Zhang et al (2013) demonstrated that application of 1.5 mM silicon improved resistance of rice to sheath blight (Rhizoctonia solani). Moreover, silicon solution at a concentration of 2 mM decreased the area under relative lesion expansion progress curve of sheath blight (R. solani) by 34.2% in rice plants (Schurt et al, 2014).…”

“…Increased activities of superoxide dismutase, ascorbate peroxidase and glutathione reductase in common bean plants reduced severity of Colletotrichum lindemuthianum (Polanco et al, 2014). Schurt et al (2014) found that the increased activities of phenylalanine ammonia-lyases, peroxidases, polyphenoloxidases and chitinases in the leaf sheaths of rice plants supplied with silicon led to the reduction in the progress of sheath blight lesions (R. solani). Increased activation of chitinase, superoxide dismutase, peroxidase and β-1,3-glucanase reduced the severity of powdery mildew (Podosphaera xanthii) in melon plants (Dallagnol et al, 2015).…”