Variability of populations of the witches' broom disease of cocoa ( Crinipellis perniciosa)

Abstract

In a study of variation in the causal agent of witches' broom disease ( Crinipellis perniciosa ) in S. America, two distinct populations of the fungus were found. Basidiocarps formed on infected cocoa ( Theobroma cacao ) differed from those found on non- Theobroma material such as the dead stems of the liana Entada gigas . Basidiocarps on cocoa (C-type basidiocarps) were smaller, of a light colour and had a different, basidiospore quotient than those found on other substrata (L-type basidiocarps). There were also some differences between the cheilocystidia of the two types. Pathogenicity tests showed that basidiospores from L-type basidiocarps could not infect T. cacao seedlings. Cultures derived from L-type basidiocarps proved to be more active saprotrophs than those from C-type basidiocarps, as measured by ability to degrade lignocellulose and sterilized Theobroma brooms and leaves. Confrontation of C-type and L-type cultures on agar indicated that they were incompatible; mutual antagonism occurred between colony margins accompanied by formation of purple pigmentation in the interaction zone. The co-existence of saprotrophic and pathogenic populations of C. perniciosa is discussed in relation to the known variability of the species throughout its range in South America.