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.