Journal of Animal and Plant Sciences
J. Anim. Plant Sci. [ISSN 2071 - 7024]
Volume 4 (1): 289 - 297. Published July 15, 2009.
The incidence and distribution of Phytophthora cinnamomi Rands on macadamia in Kenya
Mbaka J.N*^, Wamocho L.S**, Turoop L** and Waiganjo M.M**
*Kenya Agricultural Research Institute, Thika, Kenya **Jomo Kenyatta University of Agriculture and Technology, Nairobi, Kenya
^Corresponding author e-mail: jnmbaka@yahoo.com
SUMMARY
In Kenya, macadamia (Macadamia integrifolia Maiden and Betche and Macadamia tetraphylla L.A.S. Johnson) is grown by over 100,000 small-scale rural farmers. Eighty three percent of the Kenyan macadamia nuts are exported to Japan, USA and China. Root rot and stem canker are major macadamia nut production constraints. This study was carried out to establish the incidence and distribution of the causal organism (Phytophthora cinnamomi) in different macadamia growing areas of Kenya. Disease surveys were carried out between December 2005 and April 2006 in all the macadamia growing areas of Kenya. A questionnaire was administered to capture data on macadamia production practices. The location of each sampling site was marked using a Global Positioning Satellite (GPS) instrument, Gamin®. Phytophthora cinnamomi was recovered from soil and diseased plant parts by plating onto synthetic media (corn meal agar). The recovered isolates of P. cinnamomi were characterised on the basis of pathogenicity and growth. Determination of mating types was done by matching with isolates of known mating types acquired from Australia. Root rot was described as the major disease of macadamia (by 85% of the respondents in the survey areas). Reported yield losses due to macadamia root rot were as high as 36.6% in one of the districts. Disease incidence was higher in flat areas. The Phytophthora root rots affected all macadamia cultivars across the regions but the most commonly affected cultivar was M. tetraphylla. Ninety percent of the interviewed farmers reported that they did not manage the disease in any way. The results show that P. cinnamomi associated with root rots and stem canker of macadamia has a wide distribution in all macadamia growing areas of Kenya. There is need to develop, validate and disseminate the best bet technologies for management of the disease to save the macadamia nut industry in Kenya. Development of integrated pest management (IPM) options for macadamia root rot has been initiated at KARI-Thika and training of farmers and extension field officers is planned to be done through the farmer field school approach.
Key words
Macadamia, root rots, incidence, distribution
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