First report of Moniliophthora roreri causing frosty pod rot (moniliasis disease) of cocoa in Mexico

Theobroma cacao, the source of cocoa or cacao, has been cultivated in Mexico for hundreds of years, with around 37,000 farms covering 62,000 Ha in Tabasco and Chiapas dedicated to its production. In March 2005, deformed and premature ripening cocoa pods were noted in the vicinity of Ignacio Zaragoza, Pichucalco in northern Chiapas. Chocolate-coloured lesions with creamy mycelium, darkening with age, mummies (shrivelled pods) and internal necrosis were also commonly observed. By April, local sources stated that around 1000 Ha were affected by the disease in the municipalities of Pichucalco, Juárez, and Ostuacán in Chiapas and nearby Huimanguillo in Tabasco.

The distinctive symptoms suggested frosty pod rot (FPR), caused by the fungus Moniliophthora roreri. This was confirmed via colony morphology and DNA sequencing. Isolates obtained from diseased pods showed an initial whitish growth on modified V8 medium, later salmon-cream and finally dark brown, due to massive spore formation (Evans, 1981). Spores were produced in chains and were thick-walled, pale yellow and heteromorphic, but commonly (74%) globose to subglobose (5-10 µm diameter), with a further 20% ellipsoid (6-11 µm x 8-19 µm).

The internal transcribed spacer (ITS) and 28S large subunit (LSU) regions of the nuclear ribosomal DNA were amplified and sequenced with fungal specific primers ITS1-F/ITS4 (ITS) and LSU4-B/LR6 (LSU) (Aime & Phillips-Mora, In Press). The sequences obtained (GenBank accession numbers DQ222923-26) were 100% homologous to those from other M. roreri isolates from Panama, Costa Rica, Nicaragua, Honduras and Belize. Two isolates obtained from diseased pods are deposited in the U.S. National Fungus Collection (herbarium BPI) as MCA 2952 and MCA 2953.

M. roreri began spreading north from Panama in 1956 (Orellana, 1956) and has now reached the northern limit of cocoa cultivation in continental America. This is the first report of FPR in Mexico, where production is now threatened by one of the most devastating cocoa diseases.