Comparative efficacies in vitro of antibacterial,fungicidal, antioxidant,and herbicidal activities of momilatones A and B

Abstract

Momilactones A (M_A) and B (M_B) are phytoalexins derived from rice plant (Oryza sativa) and were considered to be a part of the mechanism of rice self-defense system. The present study was to evaluate the comparative efficacies in vitro of antibacterial, fungicidal, antioxidant, and herbicidal activities of M_A and M_B. In general, M_B shows higher antifungal, antibacterial, and herbicidal action than M_A, although its antioxidant property was less than M_A. In herbicidal trial, the IC₅₀ values of M_B against germination, shoot and root elongation of barnyardgrass and monochoria were 40.9, 45.5, and 27.5, and 27.1, 17.3, and 0.9 µg, respectively. For M_A, these values were 40.3, 35.6, and 55.1, and 43.9, 24.3, and 0.5 µg, respectively. For antifungal activity, momilactone B (IC₅₀: 1.2, 123.9, and 53.4 µg) exerted significantly greater inhibition than M_A (IC₅₀: 78.1, 198.1, and 95.3 µg) against Botrytis cinerea, Fusarium solani, Colletrotrichum gloeosporioides, respectively, except for Fusarium oxysporum that both M_A and M_B showed no marked difference. In addition, M_B exhibited significantly stronger antibacterial activity than M_A against Pseudomonus ovalis, Bacillus cereus, and Bacillus pumilus, whereas the inhibitory activity of the two compounds was similar against Escherichia coli. Both M_A and M_B exerted rather weak antioxidant activity (EC₅₀ was 783.9 and 790.7 µg, respectively), of which M_A showed a slightly stronger antioxidant activity than M_B. This study is the first to examine antifungal, antibacterial, and antioxidant activities of two phytoalexins, as well as their comparative efficacies against growth of the noxious weeds barnyardgrass and monochoria.