Induction and accumulation of caffeine in young, actively growing leaves of cocoa (Theobroma cacao L.) by wounding or infection with Crinipellis perniciosa

Abstract

Crinipellis perniciosa, the causal agent of witches' broom disease, attacks young actively growing shoots, flowers and developing fruits of cocoa (Theobroma cacao L.). Infected shoots become fasciated and a profusion of hypertrophic shoots with small leaves develop from the lateral buds. This is followed by desiccation and death of the infected stem and leaves. Infected stem tissue contains significant amounts of caffeine (109±35μg g−1), approximately seven to eight times greater than healthy stems (14±1μg g−1). Wounding young actively growing leaves induces the production of considerable amounts of caffeine within 1day of treatment, whereas the level of caffeine in older leaves is unaffected by wounding. Caffeine production is stimulated by treatment of young actively growing leaves with salicylic acid (SA) and its synthetic analog, benzothiadiazole, compounds that induce pathogen defense responses in plants. Growth of C. perniciosa is also significantly inhibited on caffeine-containing media. The results suggest that in cocoa, the caffeine pathway is inducible in young actively growing leaves by pathogen attack, wounding and SA, and may be part of the defense response of this species to herbivory and infection.