Assessing resistance to Crinipellis perniciosa using cocoa callus

Callus cultures from cocoa clones reported to have different susceptibilities to Brazilian isolates of Crinipellis perniciosa , causal fungus of witches' broom disease, including Catongo (susceptible). Scavina-6, CAB 64 and CAB 67 (resistant) were inoculated with basidiospores of C. perniciosa and the subsequent development of mycelia was assessed. Generally, on Catongo callus, mycelium similar to that found in green brooms (parasitic type), developed abundantly but on callus from Scavina-6 and the two CAB clones, mycelial growth was relatively poor and tended to be similar to that in dry brooms and on agar media (saprotrophic type). There was often considerable variation in fungal development on individual callus cultures from the same clone, but there was an overall consistency between successive experiments in ranking the callus material in terms of fungal development. However, growth of isolates from Colombia and Trinidad was similar on callus from Scavina-6 which in the field is known to reac differentially to these two isolates. Experiments with isolates from Colombia indicated that inoculum from basidiocarps produced on brooms which were kept for long periods in cabinets to induce fruiting had a decreased ability to colonize callus.