The agaric Crinipellis perniciosa (Tricholomataceae) is a hemibiotrophic pathogen which causes witches' broom disease of cacao and has recently decimated the Brazilian cacao industry. In addition to the pathogenic cacao (C-) biotype, other biotypes are found in association with unrelated plant taxa, notably bignoniaceous lianas (L-biotype), solanaceous hosts (S-biotype), and the shrub Heteropterys acutifolia (H-biotype). The Cand S-biotypes are non-outcrossing and form broom symptoms on hosts, whereas the L-biotype is outcrossing and asymptomatic. Phylogenetic analysis of several regions of the rRNA locus revealed near identity between C-and S-biotype isolates from diverse locations, with the Land Hbiotypes forming separate groupings. Preliminary analysis of sequence data from Moniliophthora roreri, causal agent of frosty pod disease, indicates that this morphologically distinct pathogen may be closely related to C. perniciosa. Similarities in host infection between C. perniciosa and M. roreri have B02084; Online publication date

Potato dextrose agar (PDA) is one of the most commonly used media for the isolation and cultivation of fungi, with morphological features and pigmentation in culture often being important for identification of cultures. Cultivation of various fungi on different brands and batches of powdered (commercial) potato dextrose media revealed deficient pigmentation in five of 10 media tested. Reduced pigmentation on these media was correlated with low levels of copper and colony colour was restored by the addition of copper. Deficient pigmentation was most pronounced when copper levels in the medium were below 50 ng mL(-1) (50 p.p.b.; 0.8 microM). Differences in pigmentation and laccase activity of spore and mycelial preparations were quantified for representative species belonging to the genera Aspergillus, Fusarium, Trichoderma, Cladosporium and Penicillium grown on PDA containing different amounts of copper. A strong positive correlation between laccase activity and copper levels was observed. Differences were also found between batches of raw potatoes, with organically cultivated tubers having higher copper levels than those grown by conventional methods, possibly because of the use of copper-based fungicides in the former case. Routine addition of 1000 ng mL(-1) copper (or standard trace element solutions) to PDA and other undefined media is advised to avoid atypical culture pigmentation and possibly other consequences of reduced activity of copper-requiring enzymes.

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