Physiological and cytological mechanisms of silicon‐induced resistance in rice against blast disease

Abstract

Rice (Oryza sativa L.) blast disease caused by Magnaporthe grisea is one of the most destructive diseases in the rice-growing areas of the world. Silicon is an important nutritional element especially for rice. Two near-isogenic lines of rice with different resistance to blast disease, i.e. CO39 (susceptible) and C101LAC (Pi-1) (resistant), were selected to determine the effects of Si amendment on the severity and incidence of rice blast disease. The physiological and cytological mechanisms involved in the induced disease resistance by silicon were investigated. Exogenous Si application at a concentration of 2 mM reduced the disease index by 45% for CO39 and 56% for C101LAC (Pi-1). Si application alone did not change lignin content and the activities of defense-related enzymes including peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) in rice leaves of both isogenic lines. However, after inoculation with M. grisea, Si-treated rice plants significantly increased the activities of POD, PPO and PAL in leaves of both isogenic lines. Si and lignin content were also significantly increased in Si-treated inoculated seedlings. Environmental scanning electron microscope observations revealed that Si amendment resulted in higher Si deposit on dumbbell bodies in the rice leaves and silicon papilla accumulation on the guard cell of stoma. These results suggest that silicon-induced defense response and cell silicification of rice leaves altogether contribute to the silicon-induced rice resistance to blast disease.

Effect of Foliar and Root Application of Silicon Against Rice Blast Fungus in MR219 Rice Variety

“…The results of this study showed that application of silica gel and sodium silicate effectively reduced the severity and incidence of rice leaf blast. These results further confirm previous reports (Cai et al, 2008;Datnoff et al, 1997;Rodrigues and Datnoff, 2005). The results also revealed that plants treated with silica gel suffered lower levels of disease severity as compared with those treated with sodium silicate.…”

“…The results also revealed that plants treated with silica gel suffered lower levels of disease severity as compared with those treated with sodium silicate. The mechanism of enhanced resistance to disease via Si application can be associated with accumulation of silicon in leaf epidermal cells which acts as a mechanical barrier against fungal infestation (Bowen et al, 1992;Cai et al, 2008). Seebold et al (2001) Showed that Si can alleviate disease severity through blocking of fungus ingress.…”

“…Seven days after inoculation, leaf blast severity was evaluated based on visual assessment of lesions caused by Magnaporthe oryzae on a nine grade scale according to IRRI standards (2002). Disease severity for each replication was calculated according to the equation below (Cai et al, 2008):…”

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

“…Higher accumulation of fungitoxic phenolic compounds due to silicon treatment protected Arabidopsis from powdery mildew caused by Erysiphe cichoracearum (Ghanmi et al, 2004;Fauteux et al, 2005). Increased activity of antimicrobial glycosylated phenolics, diterpenoid phytoalexins, and lignin decreased severity of blast disease in silicon-treated rice plants (Cai et al, 2008). Dallagnol et al (2011) found that decreased level of rice brown spot (Bipolaris oryzae) was due to enhanced accumulation of lignin and soluble phenolics.…”

“…Enhanced peroxidase activity in wheat leaves, due to silicon treatment, decreased the severity of powdery mildew caused by Blumeria graminis f.sp.tritici (Yang et al, 2003). Regarding the rice-M. oryzae interaction, increased resistance against the blast pathogen is characterized by higher accumulation of glucanase, peroxidase, polyphenol oxidase and phenylalanine ammonia-lyase (Rodrigues et al, 2003(Rodrigues et al, , 2004(Rodrigues et al, , 2005Cai et al, 2008). Liang et al (2005) found that enhanced peroxidases, polyphenoloxidases and chitinases activities due to silicon root application were eff ective in reducing powdery mildew severity in cucumber.…”