The breeding biology of biotypes of the witches' broom pathogen of cocoa, Crinipellis perniciosa

Abstract

Investigation of the breeding biology of the agaric Crinipellis perniciosa (causal agent of witches' broom disease of cocoa in South America) found that two distinct breeding strategies exist among the four known biotypes of the fungus, which are specific to cocoa (C-biotype), solanaceous hosts (S-biotype), Bixa orellana (B-biotype) and liana vines (L-biotype). The homomictic (primary homothallic) behaviour of the C-biotype was confirmed and single basidiospore isolates (SSIs) of the S-biotype and B-biotype were found to behave in a similar manner. The mycelia of most SSIs of the L-biotype did not bear clamp connections and pairings between sibling SSIs established that an outcrossing mechanism under the control of two unlinked mating type factors was operating (i.e. bifactorial heterothallism). These matings also suggested that one of the mating factors has a two-gene structure. The occurrence of bi- and trinucleate basidiospores and SSIs bearing true or false clamp connections suggests that the L-biotype exhibits a limited degree of secondary homothallism.