Crinipellis perniciosa (Stahel) Singer, the causal agent of witches' broom disease of cocoa (Theobroma cacao L.), is one of the 63 known species of the genus Crinipellis, which is placed in the Tribus Marasmiae of Tricholomataceae, the largest family of order Agaricales. The genus Crinipellis is characterized by the pseudoamyloid hairs in pileus (Singer, 1986).

Although originally believed to be restricted to plant genera Theobroma and Herrania (Sterculiaceae), Crinipellis perniciosa has also been reported in many other quite unrelated plant hosts such as species of Solanaceae and Bignoniaceae, suggesting that there are at least four distinct biotypes: the Cocoa biotype (C-biotype), the Solanum biotype (S-biotype), the Bixa (B-biotype) and the liana biotype (L-biotype). In marked contrast to other biotypes, the L-biotype does not cause witches' broom disease symptoms on its host, exhibiting a highly restricted geographical distribution and a multialelic outcrossing mechanism (Griffith & Hedger, 1994a).

The C-biotype of Crinipellis perniciosa has a hemibiotrophic life cycle. In nature, the disease spread commonly results from the abiotic dispersal of uninucleate basidiospores released from basidiomes present in host organs. After reaching novel plant surfaces, monokariotic germtubes are produced, which actively infect meristematic cocoa tissues. The infective, biotrophic, (primary) mycelium is characterized by wide, non-clamped, intercellulary hyphae. It induces excessive and disorganized growth at apices usually resulting in multiple swollen shoots from vegetative buds, and more occasionally vegetative cushions - the green brooms. After 3-9 weeks, the fungus undergoes dikaryotization, with the invasion of host tissues by a narrower, clamped, saprotrophic, (secondary) mycelium, culminating in the death of broom tissue. The necrotic brown brooms remain attached or may fall into the canopy or to the soil. The completion of life cycle is achieved by the production of basidiomes on the surface of brown brooms 6-24 months later (Isaac, Hardwick & Collin, 1993; Purdy & Schmidt, 1996).

Crinipellis perniciosa (C-biotype) is unusual amongst Basidiomycota since it exhibits true homomixis (primary or homo-dikaryotic homothallism). According to Lemke (1969), only 1% of basidiomycete species are primary homothallic. As most self-fertile (homothallic) basidiomycetes are closely related to or taxonomically conspecific with self-sterile (heterothallic) species, it is supposed that such a breeding strategy change could involve small genetical changes. Although the coincident inactivation of both of mating type factors of a bifactorial heterothallic ancestor is highly improbable, it cannot be ruled out that such a change could occur via inactivation of only one of the two mating type loci in individuals of an unifactorial population, which has not been found in nature yet. (Griffith & Hedger, 1994b). As heterothallism is the prevailing condition of heterobasiomycota fungi, it is tentative to consider true homothallism as an apomorphic condition in the homobasidiomycete Crinipellis perniciosa.

There is no molecular phylogenetic study, which includes Crinipellis perniciosa. In a recent work, one species of the genus Crinipellis (Crinipellis maxima) comes closer to two Marasmius species in a same clade (Moncalvo, 2000) as would be expected in morphology-based classification schemes.

Griffith, G. W. & Hedger, J. N. (1994a). Spatial distribution of mycelia of the liana (L) biotype of the agaric Crinipellis perniciosa (Stahel) Singer in tropical forest. New Phytol. 127:243-259.

Griffith, G. W. & Hedger, J. N. (1994b). The breeding biology of the witches' broom pathogen of cocoa, Crinipellis perniciosa. Heredity 72:278-289.

Isaac, S., Hardwick, K. & Collin, H. (1993). Interactions between the pathogen Crinipellis perniciosa and cocoa tissue. In Aspects of Tropical Mycology (eds S. Isaac, J. C. Frankland, R. Watling & A. J. S. Whalley), pp.219-232. Cambridge University Press: Cambridge, U.K.

Lemke, P. A. (1969). A reevaluation of homothallism, heterothallism and the species concept in Sistotrema brinkmanii. Mycologia, 61:57-76

Moncalvo, J-M, Lutzoni, F. M., Rehner, S. A., Johnson, J. & Vilgalys, R. (2000). Phylogenetic relationships of agaric fungi based on nuclear large subunit ribosomal DNA sequences. Systematic Biology 49:278-305

Purdy, L. H. & Schmidt, R. A. (1996). Status of cacao witches' broom: biology, epidemiology and management. Annu. Rev. Phytopathol. 34:573-594.

Singer, R. (1986). Agaricales in Modern Taxonomy. Koeltz Scientific Books: Koeningstein.