Zinniol,a phytotoxin,is produced by Phoma macdonaldii

Zinniol, a phytotoxin, has been isolated from culture filtrates of Phoma macdonaldii, the causal agent of stem blight of sunflower (Helianthus annuus L.). The production of zinniol appears to be regulated by one or more compounds in the sunflower plant. Zinniol has been isolated from tissues infected with P. macdonaldii implicating it in the disease process. The hypocotyls of sunflower cultivars react differently to zinniol when injected with concentrations from 3.75 × 10⁻³ M to 7.5 × 10⁻³ M. In the most sensitive reaction, zinniol causes the production of a sunken, discolored lesion.