PHYTOTOXIC AND ANTIMICROBIAL ACTIVITY OF 5,7-DIHYDROXYCHROMONE FROM PEANUT SHELLS

A flavonoid decomposition product that is present in peanut (Arachis h ypogaea) shells, 5,7-dihydroxychromone (DHC), was found to inhibit the radial growth of cultures of the soil pathogenic fungi Rhizoctonia so lani and Sclerotium rolfsii with I-50 (the concentrations of DHC requi red to inhibit growth 50%) values of 18 and 26 mu M, respectively. Rad icle elongation of velvetleaf, corn, peanut, and wheat was inhibited b y DHC with I-50 values of 30, 50, 65 and 200 mu M, respectively. DHC h ad no effect on the growth of Bradyrhizobium sp. at 10 mu M in medium containing low (1.0 g/liter) mannitol as the carbon source, although t he related flavones luteolin and chrysin each promoted bacterial growt h at 10 mu M 48 hr after inoculation. When tested in high (10.0 g/lite r) mannitol medium, DHC initially inhibited growth of Bradyrhizobium s p., but 120 hr after inoculation the growth of all treatments were sim ilar. These results suggest a role for DHC released from peanut shells in suppressing pathogenic fungal infection and competing plant growth but not for Bradyrhizobium growth promotion.