Growth rates of, and mycelial interactions between, isolates of Crinipellis perniciosa from cocoa

Growth of 87 single‐basidiospore isolates of Crinipellis perniciosa, derived from witches' brooms on cocoa in 10 localities throughout South America and the Caribbean, was examined at 25°C on five agar media (Czapek‐Dox, prune extract, potato‐dextrose, V8 and carboxymethylcellulose). Interactions (designated intermingling or mutually antagonistic) between paired mycelia of 64 isolates were determined on V8 plates. Six somatic‐compatibility groups were identified comprising isolates from; (1) Pichilingue and Rio Palenque in Ecuador, Chigorodo and Manizales in Colombia; (2) Sucua (Ecuador); (3) Manaus (Brazil); (4) Ouro Preto (Brazil); (5) Castanhal (Brazil); (6) Trinidad and Tobago. This geographical separation of isolates was supported by results of the growth tests; growth of isolates within each compatibility group differed from other groups on at least one of the five media. Separation of isolates by these methods did not conflict with previous results from tests of pathogenicity and could be useful in selecting isolates for screening cocoa lines for resistance to C. perniciosa.