phytoalexin

A chemical produced by a host plant that inhibits the growth of a pathogenic fungus. For example, the phenolic compound pisatin has been shown to accumulate in pea tissues in the presence of various fungi. Similarly the degree of resistance shown by sweet potato (Ipomoea batatas) to attack by the fungus Ceratostomella has been correlated with the concentration of the terpenoid ipomeamarone in the plant tissue.