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Root Decay Caused by Kretzschmaria clavus: Its Relation to Macadamia Decline. W. H. Ko, Professor, Department of Plant Pathology, University of Hawaii, Beaumont Agricultural Research Center, Hilo 96720; R. K. Kunimoto(2), and I. Maedo(3). (2)(3)Research Associates, respectively, Department of Plant Pathology, University of Hawaii, Beaumont Agricultural Research Center, Hilo 96720. Phytopathology 67:18-21. Accepted for publication 9 August 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-18.

Colonies similar to those originating from ascospores of Kretzschmaria clavus were isolated consistently from advancing margins of decay in macadamia roots. Like naturally infected roots, tissues were decayed and black lines were formed when healthy roots were inoculated with root tissues colonized by K. clavus originating from both decayed tissue and ascospores. The pathogen was reisolated from diseased tissues of artificially inoculated roots. At Hilo and vicinity more than 80% of declining macadamia trees had extensive root decay caused by K. clavus. Severity of tree decline was positively correlated with amount of root decay.

Additional keywords: Macadamia integrifolia, Xylariaceae.