PREFORMED AND INDUCED CHEMICAL RESISTANCE OF TEA LEAF AGAINST EXOBASIDIUM VEXANS INFECTION

Levels of (-)-epicatechin in tea cultivars (Camellia sinensis) resistant to blister blight leaf disease (Exobasidium vexans Massee) were significantly higher than those in susceptible cultivars, while the reverse was true for (-)-epigallocatechin gallate suggesting that epicatechin was involved in the resistance mechanism. The content of the methylxanthines, caffeine and theobromine in the leaf increased significantly in the initial translucent stage of the disease, probably as a defense response to fungal attack. Epicatechin and epigallocatechin levels were significantly less than in healthy tissues at this stage, but increases in the corresponding gallate esters suggested that they were being converted into esters. Although epicatechin and epigallocatechin levels decreased from translucent to mature blister stages, the decrease was not significant. The decrease in levels of epicatechin, epigallocatechin and their esters on infection and the formation of cyanidin and delphinidin on oxidative depolymerization of the blisters suggest that proanthocyanidins may play a role in the defense mechanism. The very high resistance of a purple-green leafed cultivar is attributed to the additional catechin source provided by the high levels of anthocyanins present. Cyanidin and delphindin were identified as tw