Antifungal activity of rapamycin onBotryosphaeria dothideaand its effect against Chinese hickory canker

BACKGROUND The trunk canker caused byBotryosphaeria dothideais a devastating disease for Chinese hickory (Carya cathayensis) in China. Chemical fungicides are commonly and repeatedly applied to control the disease; however, fungicide application raises major environmental and food safety issues. Ecofriendly biocontrol alternatives were urgently needed. Herein, the antifungal activity of a natural secondary metabolite, rapamycin, againstB. dothideaand the effect of a rapamycin-producingStreptomyces hygroscopicusonC. cathayensiscanker were investigated. RESULTS The 50% effective concentrations (EC50) of rapamycin against mycelial growth and spore germination on the potato dextrose agar were 5.1 x 10(-3)and 5.5x 10(-2)mu g mL(-1), respectively, which were much lower than the EC(50)values of thiophanate-methyl. The hyphae ofB. dothideaexhibited premature aging and wrinkling after treatment with rapamycin at 5.0 x 10(-3)mu g mL(-1). A rapamycin-producing bacteriumS. hygroscopicusLYJ637 was batch produced and formulated in a carboxymethylcellulose/poly (vinyl alcohol) (CMC/PVA) blend and used for testing the efficiency of the bacterium in controllingBotryosphaeriacanker inC. cathayensis.S. hygroscopicusexhibited high stability in the CMC/PVA blend. Results of a 3-year field experiment suggested that rapamycin formation reduced the occurrence of both developed cankers and new cankers, with an efficacy comparable to the treatment with thiophanate-methyl. CONCLUSION The rapamycin-producingS. hygroscopicusLYJ637 carried in a CMC/PVA blend prevented effectivelyBotryosphaeriacanker on Chinese hickory, which provides an alternative approach to chemical control strategies.

Automated summary

The study revealed that rapamycin has high antifungal activity against B. dothidea, and rapamycin-producing Streptomyces hygroscopicus can effectively prevent trunk canker disease on Chinese hickory, offering an alternative to chemical control methods.