GENETIC DIVERSITY AND POPULATION STRUCTURE OF MONILIOPHTHORA RORERI IN COCOA PRODUCING AREAS OF GUATEMALA

Abstract

Frosty pod rot (FPR) disease, caused by Moniliophthora roreri, is the most important cocoa disease in the Western Hemisphere. In Guatemala, the presence of the pathogen is attributed to a rapid and clonal dissemination throughout Central America after one or very few introductions of M. roreri from South America. We analyzed the genetic diversity of isolates from the main cocoa producing departments in Guatemala using AFLP. In total, 15 different multilocus genotypes were found among 119 isolates, indicating a low genetic diversity (percentage of polymorphic loci and Nei’s gene diversity, 12.28% and 0.321, respectively). The obtained linkage disequilibrium through the observed and standardized indexes of association (I_A and r̄_d) confirmed clonality and asexual reproduction in the populations of M. roreri. The discriminant analysis of principal components suggested three genetic groups; nonetheless, the minimum spanning network and fixation index (Φ_ST = 0.043 P = 0.09) revealed a weak population structure, mainly attributed to high human-mediated gene flow (Nm = 11.13). Given the high mutation rate of M. roreri, constant monitoring of its evolution is suggested along with quarantine practices that limit its dispersal and evaluation of cocoa clones tolerant to the new genotypes of M. roreri, thus preventing increases in losses of Guatemalan cocoa production.