Canopy‐microclimate effects on the antagonism between Trichoderma stromaticum and Moniliophthora perniciosa in shaded cacao

Abstract

The collective impact of several environmental factors on the biocontrol activity of Trichoderma stromaticum (Ts) against Moniliophthora perniciosa (Mp), the cause of cacao witches’ broom disease, was assessed under field conditions of shaded cacao (Theobroma cacao) in south‐eastern Bahia, Brazil. Biocontrol experiments were performed adjacent to an automated weather station, with sensors and Ts‐treated brooms placed at different canopy heights. Sporulation occurred at the same dates for all Ts isolates, but in different quantities. Broom moisture >30%, air temperature of approximately 23 ± 3°C, relative humidity >90%, solar radiation intensities <0·12 KW m−² and wind speed near zero were the key environmental parameters that preceded Ts sporulation events. A multiple logistic regression indicated that these weather variables combined were capable of distinguishing sporulation from non‐sporulation events, with a significant effect of wind speed. Analyses of environmental factors at ground level indicated similar pre‐sporulation conditions, with a soil moisture content above a threshold of 0·34 m3 m−3 preceding all sporulation events. The sporulation of five selected Ts isolates was compared at four different canopy heights. Isolates responded differently to weather variation in terms of sporulation and antagonism to Mp at different canopy levels, indicating that different microclimates are established along the vertical profile of a shaded cacao plantation. The potential of these findings for development of predictive mathematical models and disease‐management approaches is discussed.