The Endophytic Trichoderma hamatum Isolate DIS 219b Enhances Seedling Growth and Delays the Onset of Drought Stress in Theobroma cacao

Abstract

Theobroma cacao (cacao) is a tropical understory tree with sensitivity to drought. Cacao responds to drought by decreases in net photosynthesis, PS II efficiency, stomatal conductance, water potential and changes in leaf florescence. Drought also alters cacao gene expression as well as leaf glucose and free amino acid content. In recent years an incredible diversity of fungal endophytes has been identified in association with cacao. These endophytes are being studied for the benefits they provide to cacao including tolerance to biotic and abiotic stresses. During establishment of the endophytic association between cacao and fungal endophytes both plant and fungal gene expression are altered. The endophytic Trichoderma hamatum isolate DIS 219b delays the onset of drought stress in cacao. This delay manifests itself through enhanced root growth, maintenance of stomata] conductance, water potential, net photosynthesis, and PSII efficiency, changes in free amino acid concentrations, and a delay in drought-induced changes in leaf gene expression. The cacao plant and DIS 219b adapt to each other and this adaptation may contribute to the observed plant growth promotion and the delay in onset of drought stress. The increase in root growth is thought to increase water uptake and availability, delaying the time point where the water supply becomes limiting and drought stress occurs.