Evaluation of cacao (Theobroma cacao) clones against seven Colombian isolates of Moniliophthora roreri from four pathogen genetic groups

Abstract

Artificial pod inoculation was used to compare the relative aggressiveness of seven Colombian isolates of Moniliophthora roreri (the causal agent of moniliasis or frosty pod disease), representing four major genetic groupings of the pathogen in cacao (cocoa), when applied to five diverse cacao genotypes (ICS‐1, ICS‐95, TSH‐565, SCC‐61 and CAP‐34) at La Suiza Experimental Farm, Santander Department, Colombia. The following variables were evaluated 9 weeks after inoculation of 2‐ to 3‐month‐old pods with spore suspensions (1·2 × 105 spores mL−1): (i) disease incidence (DI); (ii) external severity (ES); and (iii) internal severity (IS). IS was found to be of greatest value in classifying the reaction of the host genotype against M. roreri. Genetic variation reported between isolates and cacao genotypes was not matched by similar diversity in their aggressiveness. All isolates were generally highly aggressive against most cacao genotypes, with only two isolates showing reduced IS and ES reactions. There was considerable variation between clones in the IS and ES scores, but one cultivated clone (ICS‐95) displayed a significant level of resistance against all seven isolates. This clone may be useful in cacao breeding initiatives for resistance to moniliasis of cacao.