Biology and epidemiology of Moniliophthora roreri, causal agent of Moniliophthora pod rot of cacao
Moniliophthora pod rot (MPR) is one of the main factors limiting cocoa production in Latin America. Currently insufficient information on the biology and epidemiology of the pathogen limits the development of efficient management options to control MPR. The purpose of this study was to identify meteorological and production variables as epidemiological predictors of the MPR disease and, coupled with the existing evidence on the MPR-cacao pathosystem, to develop a conceptual model. Information obtained is strategic for better understanding of the pathosystem, to guide researchers to define new studies and to improve control methods. The research began with a historical data analysis to determine the influence of the meteorological, productive and genetic resistance variables on the disease over time. This analysis revealed that the resistance of the highly resistant clones is considerably stable and possibly durable; however, for the rest of the clones, disease reaction was shown to be significantly influenced by the environment. Also, temperatures during January, April and May are the only climatic variables that have a significant effect over MPR incidence. A field trial was then carried out to explain MPR development, onset of symptoms of the disease and fungal sporulation, studying different microclimatic variables for three cacao clones in a range of incomplete resistance. We concluded that water-related variables (positively linked) and temperature (minimum temperature negatively linked while maximum temperature presented a threshold) determine symptom expression for the susceptible clones, while, for the resistant clone CATIE-R4, only temperature (minimum temperature negatively linked and maximum temperature positively linked) showed up as an explicative variable, due to low numbers of CATIE-R4 pods showing symptoms. Differences in resistance among these clones possibly lie in the number of resistant genes accumulated; however, the resistance of the three may be affected by certain environmental conditions. To separate the microclimatic effects on the infection and the symptoms onset, we studied the relationship between the MPR infection process and the onset of symptoms of three different cacao clones through artificial inoculations. We determined that symptoms/signs onset is close enough to the infection moment that the influence of the microclimate over onset of the symptoms could be extrapolated to the time of infection.