Trichoderma asperellum: A Dominant Endophyte Species in Cacao Grown in Sulawesi with Potential for Controlling Vascular Streak Dieback Disease

Abstract

Endophytic strains of Trichoderma species can be used as an alternative to chemicals to control vascular streak dieback (VSD) disease of cacao. Of 21 Trichoderma isolated from Theobroma cacao (cacao) in Indonesia, 19 were identified as Trichoderma asperellum. Four isolates of this species (ART-4, ART-5, ART-6 and ART-8) were reintroduced into young cocoa seedlings by root inoculation and after 4 weeks all were recovered from roots and stems, while ART-4 and ART-5 were recovered from leaves as well. Spraying seedlings pre-inoculated with T. asperellum ART-4, ART-5 and ART-6 with mycelium of the VSD pathogen Ceratobasidium theobromae resulted in no apparent VSD symptoms on the leaves. Those seedlings pre-inoculated with ART-8 showed 8.9 % incidence of VSD symptoms on the leaves when compared to a 20.4 % incidence of VSD on positive control leaves, 12 weeks after inoculation. The same isolates were also reintroduced into 3-month-old cocoa seedlings via the connecting site following shoot grafting, and after 12 weeks all isolates were recovered from stem and leaves. Seedlings grafted with buds infected by VSD and treated by ART-4 showed no VSD symptoms on their leaves 12 weeks after grafting and inoculation. However, those treated with ART-5, ART-6 and ART-8 showed 33.3 %, 50.0 % and 56.0 % incidence of VSD symptoms on their leaves, respectively, compared to an 88.9 % incidence of VSD on positive control leaves. Therefore, the study results demonstrates for the first time the potential of T. asperellum isolates to control VSD disease on cacao.