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Effects of microclimatic variables on the symptoms onset of Moniliophthora roreri, causal agent of Moniliophthora Pod Rot in cacao

Leandro Munoz M.E., Tixier P., Germon A., Rakotobe V., Phillips-Mora W., Maximova S.N., Avelino J.. 2016. In : Frontiers in science and technology for cacao quality, productivity and sustainability. State College : Penn State University, p. 60-60. Symposium Frontiers in Science and Technology for Cacao Quality, Productivity and Sustainability, 2016-05-31/2016-06-02, State College (Etats-Unis).

Moniliophthora Pod Rot (MPR), caused by the fungus Moniliophthora roreri (Cif.) Evans et al is one of the main limiting factors of production in Latin America. Combating MPR is difficult due to the time-consuming and high cost recommended practices. This limitation is due to the current insufficient information on the biology and epidemiology of the pathogen. This research aims to explain MPR development through the following microclimatic variables: daily average, minimum and maximum temperatures and relative humidities and wetness frequency, in the susceptible cacao clone Pound 7. A total of 2268 pods of 5-10 cm length were labelled during 55 weeks. Pods were observed throughout their lifetime: healthy, diseased with no sporulation, diseased with sporulating lesions, harvested. Using GLMM and AIC surfaces we determined the specific period (when and for how long) where each variable better explained the disease development. These new variables were combined in a complete GLMM, where only significant variables were retained. Wetness Frequency from day 14 to day 1, before labelling, and Maximum Temperature from day 4 to day 21, after labelling, were the most explicative variables for the symptoms' appearance. The former was positively linked with the symptoms' appearance when the later exhibited a maximum at 30°C. For sporulation the most explicative variables were Minimum Temperature from day 35 to day 58 and Maximum Temperature from day 37 to day 48, both after labelling. The former was negatively linked with the sporulation when the later was positively linked. Results indicate that the fungal climatic requirements vary from the early to the late cycle stages, corresponding to the pathogen's long latent period. This information is valuable to develop new conceptual models for MPR in order to high- light any weaknesses in its life cycle and take advantage of it to establish low-cost and efficient control methods. (Texte intégral)

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