(+)-catechin acts as an infection-inhibiting factor in strawberry leaf

An infection-inhibiting factor (IIF) was isolated from strawberry leaves an d identified as (+)-catechin. This compound inhibited the formation of infe ction hyphae from appressoria of Alternaria alternata, but allowed both spo re germination and appressorial formation. It is a normal component of stra wberry leaves, but further accumulates as the major IIF in response to inoc ulation with nonpathogenic spores of A. alternata. The accumulation of (+)- catechin on a susceptible host was not induced, however, by inoculation wit h pathogenic spores of the strawberry pathotype or by inoculation with nonp athogenic spores supplemented with host-specific toxin (AF-toxin I). These results imply that (+)-catechin acts as a protective agent during induced r esistance and that AF-toxin I acts as a fungal suppressor of induced resist ance.