Effect of Rhizoctonia spp. on Polyphenol Oxidase Enzyme Activity in Alfalfa Seedling

Abstract

Soil borne diseases cause significant losses on quantity and quality of many crop species annually. Rhizoctonia is a widespread and ecologically diverse soilborne fungus causing different types of diseases in many plant species including alfalfa (Medicago sativa). Rhizoctonia species have been traditionally identified based on the cell nuclear condition. Polyphenol oxidases (PPOs) are ubiquitous copper-containing enzymes that are widely occurring enzymes among plants. PPOs are involved in the oxidation of polyphenols into quinones (antimicrobial compounds) and lignification of plant cells that contribute to the formation of defense barriers against pathogens. The study was conducted with the aim to determine the effect of indigenous isolates of a multinucleate (Rhizoctonia solani AG-4) and nineteen isolates of binucleate Rhizoctonia on PPO activity in alfalfa (cv. Gea) seedling under in vitro conditions. The activity of PPO enzyme was determined in inoculated and uninoculated control alfalfa plants after ten days from inoculation. There was a significant increase in the activity of PPO after treatment of alfalfa seedling with isolates of Rhizoctonia. Among Rhizoctonia isolates, highest induction of PPO activity was recorded with pathogenic R. solani AG-4. In present study, increased amounts of PPO were also observed in plants that were challenged with Rhizoctonia spp. PPO has a role in catalyzing phenolic oxidation in limiting disease development. PPO may therefore be involved in induction of defense resistance against plant diseases.