Effects of Rhizoctonia solani infection on physiological and biochemical changes in mungbean (Vigna radiata L.Wicks)

Rhizoctonia solani is an important soil-borne pathogen that devastated mung bean plants in Indonesia. Until now, there are no varieties that are resistant to infection with this pathogen. Thirty mung bean genotypes from different countries were evaluated for R. solani resistance. The changes in the physiology and biochemistry of mung beans affected by R. solani infection were investigated. This study showed that thirty genotypes tested were clustered into three groups by Euclidean distance and ward's method based on a number of damping-off incidents, mortality rate, and a number of pods. R. solani infection causes physiological damage such as necrosis of guard cells, tissue collapse, and plant death, particularly in the early stage of plant growth. Seed rot, cotyledon rot, and damping-off were the three most prevalent symptoms. The shoot and root fresh weight, shoot and root length, as well as the number of pods, were reduced due to R. solani infection. Total phenolic and flavonoid content increased in mung bean seedlings under stress conditions. However, antioxidant activity was lower compared to the control untreated plant. As a response to disease attacks, phenylalanine ammonia-lyase (PAL) and tyrosine ammonia lyase (TAL) accumulations in the tolerant variety were remarkably higher than those in a susceptible variety. A similar trend was also observed in peroxidase and polyphenol oxidase activity. The results obtained in this study indicate that the mung bean resistance mechanism against R. solani was related to the synthesis of phenolic metabolites.