Attack on tea by Xyleborus fornicatus: Inhibition of the symbiote, Monacrosporium ambrosium, by caffeine

Abstract

Methylene chloride extracts of tea ( Camellia sinensis), stems from two clones, TRI 2023 and TRI 2025, inhibited growth of the fungus, Monacrosporium ambrosium, the symbiote of the shot-hole borer beetle, Xyleborus fornicatus. Activity-guided fractionation of the extracts yielded caffeine as the major antifungal compound. The caffeine content of healthy pencil-thick stems of the two clones was estimated and compared with the caffeine content of pencil-thick stems infected by the beetle. Healthy stems of clone TRI 2023 had a very low caffeine content, but accumulation of caffeine was found to have occurred to a greater extent in infected samples of stems from this clone. Infected stems from both clones had a higher caffeine content than samples of healthy stems. The effect of caffeine on mycelial growth, sporulation and spore germination of M. ambrosium in liquid and agar media was also studied. Inhibition of mycelial growth was observed with 5000 ppm of caffeine, while 500 ppm resulted in 21% inhibition in the liquid medium. In the agar medium, colony-size was reduced by 500 ppm of caffeine, while no growth took place with 5000 ppm of caffeine. Inhibition of sporulation was observed with 2000 ppm of caffeine. Germination of conidia was inhibited completely with 3750 ppm of caffeine; inhibition was also observed with 500–2500 ppm of caffeine.