Efecto de los factores macro y microclimáticos y las características productivas del cacao sobre la epidemiología de la moniliasis

Cocoa, diseases, especially the frosty pod rot, produced by the fungus Moniliophthora roreri (Cif.) Evans et al (Basidiomycetes, Marasmiaceae) are the main limiting factor of production in Latin America. This pathogen is aggressive and easily dispersed. Also, most commercial genotypes of cacao in the region are susceptible. The arrival of this pathogen to the Caribbean, Brazil and West Africa (largest producer area) can cause devastating effects in the global cocoa production. Combating moniliasis is difficult due to the time-consuming recommended practices. Moreover, there is currently insufficient information of the pathogen, thus it is essential to further study the basic aspects of the pathogen, the epidemiology of the disease and the climatic and production factors that affect the development of the epidemic, in order to achieve effective, simple and lasting control methods. The present investigation studied on the effect of macro and microclimatic factors such as precipitation, temperature and relative humidity as well as the production of cocoa on the initiation, development and impact of the moniliasis in the Atlantic Coast of Costa Rica. The research was divided into two parts. The first was an analysis of historical data (yield, climatic and phenological data) collected over 9 years by CATIE´s Cacao Breeding Program. The collection was utilized to generate regression trees from the accumulated data in order to rank the most relevant descriptors over the incidence of moniliasis in the different cacao clones over time. The second part was based on a field trial to study the microclimate (temperature, relative humidity and wetness) of each fruit and its correlation with the epidemiological development of the disease. While, two Campbell microclimate data loggers were placed on shade contrasting conditions. Also, a Burkard trap was also placed in the experimental area in order to quantify the amount of airborne spores present throughout the trial. The first part of the research determined that the most important variables explaining the annual incidence of moniliasis are "clone", "tree", "production" and "temperature" respectively. The "clone" variable divided the total number of studied plots in 7 groups according to their level of resistance or susceptibility to the pathogen. In the highly resistant clones group highlighted the CATIE-R2, CATIE-R4 and CATIE-R6, while in the highly susceptible clones group appeared the CATIE-1000, POUND-7, SCA-6 and SCA-12. The "year" variable indicated that in years 3, 5 and 6 of this experiment showed the lowest number of infected pods. According to the variable "production" higher pod production increased incidence of this disease. Finally, the highlighted average temperatures in this analysis were January, July and August temperatures. During these months, average temperatures above 23,1°C; 25,2°C and 25°C respectively, increased the number of infected pods. Field trial determined that there is evidence that moniliasis is a monocyclic disease: only one disease cycle for one generation of pods. The illusion of an epidemic was given by the continuous fruiting on cacao trees throughout the year, providing susceptible tissue to the fungus at all times. Regarding the effect of microclimatic factors within the investigation, air and fruit temperature at the first 21 days of its existence were the only variables affecting microclimatic growth rates of the disease in different generations of fruit. Furthermore, the optimum temperature range for the development and reproduction of M. roreri is 24-28°C in vivo. Also, it was discovered that the age of the fruit and the microclimate conditions may vary the symptomatic picture of disease over time, accelerating the progress and causing that some symptoms were not detected as the temperature and the number of susceptible young fruits increased. Shade conditions of the plots also affect the incidence of this disease by directly affecti