Bionic fungicide physcion controls gray mold in tomato: possible modes of action

In this investigation of the efficacy of the natural product physcion for the control of gray mold of tomato in the field and possible modes of action, physcion was significantly less effective in in vitro antifungal tests than synthetic fungicides pyrimethanil and boscalid. However, in greenhouse tests, physcion dramatically reduced the severity of gray mold on tomato plants. We further found elevated activity of several enzymes associated with the synthesis of phenolic compounds and plant defense reactions, including phenylalanine ammonia-lyase, peroxidase, and polyphenol oxidase. Physcion also significantly increased plant growth, indicating that it can also act as a growth promoter in tomato. The results from two consecutive years of field trials revealed that the application of physcion at a rate of 9 g a.i./ha reduced disease incidence between 63.44 and 69.79%, comparable to the fungicide pyrimethanil. Together, these results indicate that although physcion had little direct effect on the growth of B. cinerea , it increased tomato performance by stimulating an endogenous plant defense response and acting as a growth promoter. The study therefore provides strong evidence that physcion provides an alternative treatment for the management of gray mold in organic and low input tomato production and in traditional integrated pest management programs.