Phytotoxic and antimicrobial activity of 5,7-dihydroxychromone from peanut shells.

A flavonoid decomposition product that is present in peanut (Arachis hypogaea) shells, 5,7-dihydroxychromone (DHC), was found to inhibit the radial growth of cultures of the soil pathogenic fungiRhizoctonia solani andSclerotium rolfsii with I50 (the concentrations of DHC required to inhibit growth 50%) values of 18 and 26µM, respectively. Radicle elongation of velvetleaf, corn, peanut, and wheat was inhibited by DHC with I50 values of 30, 50, 65 and 200µM, respectively. DHC had no effect on the growth ofBradyrhizobium sp. at 10µM in medium containing low (1.0 g/liter) mannitol as the carbon source, although the related flavones luteolin and chrysin each promoted bacterial growth at 10µM 48 hr after inoculation. When tested in high (10.0 g/liter) mannitol medium, DHC initially inhibited growth ofBradyrhizobium sp., but 120 hr after inoculation the growth of all treatments were similar. These results suggest a role for DHC released from peanut shells in suppressing pathogenic fungal infection and competing plant growth but not forBradyrhizobium growth promotion.