Armillaria root rot of theobroma cacao

Abstract

Armillaria root rot of Theobroma cacao was reported for the first time more than a century ago. The pathogen causes a root rot of these trees, resulting in tree death. Mortality commonly occurs in distinct disease centers, often around stumps of dead native trees removed for the establishment of cacao orchards. The cause of Armillaria root rot was, and often continues to be, ascribed to Armillaria mellea. Advances in fungal taxonomy have, however, shown that A. mellea is restricted to eastern Asia, Europe, and North America and that the cause of Armillaria root rot of cacao, in for example Africa, represents a distinct species. Management of Armillaria root rot is often unsuccessful due to the persistence of fungal inoculum in roots, stumps, and soil. Some success has been achieved in managing the disease in other crops, but due to the relatively low acknowledged incidence of Armillaria root rot in cacao plantations, limited experience in controlling the disease exists for this crop. Care should be taken, however, as the impact of root and wood rot pathogens such as Armillaria species results not only in tree death but also in reduced tree vigor and yield. The availability of genomes for both T. cacao and Armillaria species provides valuable opportunities for future endeavors to reduce the impact of this disease in cacao plantations.