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Title: Canopy-microclimate effects on the antagonism between Trichoderma stromaticum and Moniliophthora perniciosa in shaded cacao

item Collins, Ronald

Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2009
Publication Date: 8/11/2009
Citation: Loguercio, L.L., Santos, L.S., Pomella, A.W., Miranda, R.A., Souza, J.T., Collins, R.T. 2009. Canopy-microclimate effects on the antagonism between Trichoderma stromaticum and Moniliophthora perniciosa in shaded cacao. Plant Pathology. 58(6):1104-1115.

Interpretive Summary: Research into diseases of cacao are important to the USA economy because this the raw material for the production of chocolate and the production of chocolate is one of the main consumers of dairy, nuts, oils and sugar products. One of the major diseases of cacao that has devastated cacao production and cause political, economic and social problems in the Western Hemisphere is Witches’ Broom Disease. One method of controlling the disease is to use a fungus (biocontrol agent) to attack the disease causing fungus. The results, in the past, have been inconsistent due to variations in the environment. The purpose of these experiments was to grow both fungi in a cacao field while monitoring environmental conditions above and below the trees. From these studies we have determined how temperature, humidity and rainfall affect both fungi in different parts of the canopy. This knowledge is of extreme importance because shade grown cacao helps to preserve the endangered Rain Forests. This work will be useful to researchers and biologists studying biological control methods and has direct applications in the field.

Technical Abstract: Despite some successes, the large-scale use of biological control in the field is still limited by inconsistencies, mostly caused by variation in the environment. This is mostly true for the biological control of the witches’ broom disease of cacao (Theobroma cacao L.) that is caused by Crinipellis perniciosa (Cp), which utilizes the mycoparasite Trichoderma stromaticum (Ts) as a biocontrol agent (BCA). By using an integrated analytical approach, we evaluated the simultaneous interference of several environmental factors on the biology of Ts, under typical cacao-growing conditions in the field in tropical, shaded plantations in southeastern Bahia (Brazil). Biocontrol experiments were performed around an automated weather station, set to continuously record several meteorological parameters, such as temperature and humidity for the air, soil and brooms, as well as rainfall, solar radiation and wind speed. The Ts-inoculated cacao-stem segments (brooms) and the station sensors were placed above and below the cacao-tree canopy, and on the ground. The results clearly demonstrated that the microclimatic effects on the biology of the BCA are related to short periods of specific variation patterns of the weather factors preceding the incidence of conidia production (sporulation) by Ts, which, in turn, determined the final Cp-biocontrol outcome. The sporulation of Ts was 16.3 % at 5.5 M and 30.4% at 1 M. The disease incidence was 17.6% at 5.5 M and 5.9% at 1 M. Beyond the well-recognized importance of humidity and temperature, the data also suggested a major interference of solar radiation and precipitation on the Ts-Cp antagonistic interaction, as well as isolate-specific and canopy level effects. Nevertheless, few off-pattern events occurred in the microclimate-Ts biology interaction, for which some complementary explanations were presented. The potential applications of these findings in the development of more cost-effective schemes for field applications of the BCA, as well as in environmentally sustainable disease management approaches are discussed