Degree of domestication influences susceptibility of Theobroma cacao to frosty pod rot: a severe disease devastating Mexican cacao

Background: The three-main cacao (Theobroma cacao) varieties cultivated in Mexico are: Criollo, Forastero, and Trinitario. Each variety has a different fruit setting time and has been subjected to several selection stages. The aim of this study was to determine the susceptibility of the three cacao varieties to Frosty pod rot caused by Moniliophthora roreri. We also analyzed the physicochemical properties of the pericarp of the three varieties and its domestication age. Question: Is there a relationship between the degree of domestication of the cacao variety and its susceptibility to Frosty pod rot? Studied species: Theobroma cacao fruits. Study site: A cacao plantation in Chiapas, Mexico. Methods: The content of moisture, lignin, phenols, peroxidase activity and hardness of the pericarp were analyzed in the middle zone of healthy fruits at 4, 8 and 12 weeks of development. Number of healthy and infected fruits were recorded every week. Results: The highest susceptibility to Frosty pod rot was found in the immature stage of fruits from the Criollo variety. The disease was mostly found in the mid-zone of the fruit. The Criollo variety was the most susceptible. This variety showed the highest moisture values and the lowest values of the other measured parameters. Conclusions: The finest cacao is obtained from the Criollo variety, the one with the highest degree of domestication, and also the most susceptible to frosty pod rot. We suggest using material from wild Criollo populations and from the Forastero and Trinitario varieties in future breeding and selection programs.