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

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 mu g, respectively. For M-A, these values were 40.3, 35.6, and 55.1, and 43.9, 24.3, and 0.5 mu g, respectively. For antifungal activity, momilactone B (IC50: 1.2, 123.9, and 53.4 mu g) exerted significantly greater inhibition than M-A (IC50: 78.1, 198.1, and 95.3 mu g) 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 mu g, 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.