SUMMARY

Organic mulches are reported to control root rot of avocado, caused by Phytophthora cinnamomi. A possible mechanism for this control is enzyme (specifically cellulase and glucanase) production by the large microbial population supported by the mulch, which can degrade the cell walls of the pathogen. Samples of a wide range of organic mulches were set out in plots at two sites for two years. Rate of decomposition, measured as change in depth, and cellulase activity in the mulch, at the mulch-soil interface and in the soil were measured. Mulches with a low rate of decomposition tended to have low levels of cellulase activity, whereas mulches that decomposed rapidly varied in their cellulase activity. Manuka and eucalyptus mulches had the highest activities. Cellulase acti-vity in the soil 5cm below the mulches was not increased by any of the mulches. Mulches taken from an avocado orchard had similar cellulase activities to mulches from the trial plots, but fresher samples (four months cf. two years) had lower activities. These findings need to be extended by establishing the level of cellulase necessary in the mulch to give control of the root rot fungus. Key Words: cellulase, Phytophthora, mulc