Induction of defence response in Oryza sativa L. against Rhizoctonia solani (Kuhn) by chitosan nanoparticles

Rice is a major food source for more than half of the world population. It is the only crop whose cultivation utilizes large area of land for food production. Recent surveys on rice production revealed that its potential yield has drastically reduced and its demand has exceeded over its production. In this context, the present study focuses on the biocontrol ability of chitosan nanoparticles (ChNP) against rice sheath blight pathogen (ShB) Rhizoctonia solani. To determine the percent disease suppression, detached leaf assay followed by greenhouse experiments were performed. The defence enzyme levels as well as the total phenol content were analysed to understand the mechanism of action of ChNP against ShB. This study recommends ChNP as a cost-effective alternative for chemical fungicides with potential biocontrol efficacy. ChNP was found to suppress 90% disease in detached leaf assay and 75% under greenhouse conditions. The enzyme specific activity of all the defence enzymes were significantly higher than the chemical control. The peroxidase, phenylalanine ammonia-lyase and chitinase enzymes were found to be the most active defence enzymes with 0.19,7.28 and 118.16 U/min/ml/mg protein compared to 0.01, 4.99 and 62.22 U/min/ml/mg protein for control. Hence, the current study suggest that ChNP, a non-toxic biodegradable biopolymer, can be an effective biocontrol agent against ShB caused by R.solani. It is a potent plant immunity booster that can be used as a suitable alternative to commercially available chemical fungicides. Further field trials in this respect are needed to determine the dosage for their application in rice fields.

Keywords: Chitosan nanoparticles; Defence enzyme; Detached leaf assay; Rhizoctonia solani.