First confirmed report of witches’ broom caused by Moniliophthora perniciosa on cacao, Theobroma cacao, in Saint Lucia

In November 2006, researchers at the Ministry of Agriculture, Forestry and Fisheries, first observed ‘witches’ broom’ symptoms on cacao trees in the Union Vale, La Dauphine, and Robot estates in Saint Lucia. The disease has since been found in other smallholder plots throughout the island. Estate managers report up to 50% of the cacao trees are infected. Diseased trees have dense, slightly curved proliferations of shoots with shortened internodes (witches’ brooms), arising from the lateral buds (Fig.1). Other symptoms include leaf necrosis, distortion and enlargement of the leaf lamina and veins, and stem swellings. Brooms in cacao are characteristic of infection by the fungus Moniliophthora perniciosa (formerly Crinipellis perniciosa).

In May 2007, samples of older, well-dried brooms were sent to the Global Plant Clinic, UK for confirmation of the pathogen. Aggregations of white saprotrophic hyphae were seen under the bark, which under microscopic examination revealed clamp connections that are characteristic of M. perniciosa. A more definitive morphological identification was obtained by inducing the fungus to produce basidiocarps. Brooms were suspended in a cabinet and subjected to a daily cycle of wetting and drying. The subsequent basdiocarps were pink, tinged with crimson and had a delicate pileus that was radially grooved with fluted edges (Fig. 2.). Fungal mycelia isolated directly from the brooms were also tested using molecular characterisation. The ITS regions of the rDNA was amplified and sequenced with fungal specific primers ITS6 (Cooke & Duncan, 1997) and ITS4 (White, et al., 1990). The sequence obtained (GenBank Accession No. EU861393) showed greater than 99% homology to 16 strains of this species held in the GenBank database.

Witches' broom of cacao is endemic to the Amazon basin region of South America, but has spread to plantations in the Americas and several Caribbean islands. This fungus can cause up to 90% pod losses and is considered to be one of the main limiting factors for cacao production in South America and the Caribbean islands (Griffith et al., 1994). The disease has previously been recorded from the Caribbean islands of the Dominican Republic, Grenada, St Vincent and Grenadines and Trinidad and Tobago, but to our knowledge this is the first confirmed report of witches’ broom in cacao from Saint Lucia.