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Disease Note.

A New Threat from Brown Root Rot of Cocoa, Caused by Phellinus noxius, in Papua New Guinea. J. J. C. Dennis, Senior Plant Pathologist, PNG Cocoa and Coconut Research Institute, P.O. Box 1846, Rabaul, Papua New Guinea. . Plant Dis. 76:642. Accepted for publication 12 November 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0642E.

In June 1991, an 18-mo-old balsa tree (Ochroma lagopus Sw.) growing in an area previously planted with cocoa (Theobroma cacao L.) died as the result of a root infection by Phellinus noxius (Corner) G. Cunn. The first symptom was yellowing and wilting of leaves, beginning at the branch tips; in less than 2 wk, the tree was totally defoliated. A brown/black fungal crust was on the surface of the trunk at ground level, and brown encrustations covered the surface of the roots. This disease can result in significant losses of mature cocoa, and the symptoms on the infected balsa were similar to those on infected cocoa (1) or other trees. This is the first report of balsa infected with P. noxius in Papua New Guinea. The disease is of great economic importance to growers redeveloping cocoa-growing areas with new cash crops and to the government, which is researching and promoting cash crop diversification. Balsa and black pepper (Piper nigrum L.) are two of the crops being considered for such diversification, and P. noxius-infected plants of both species were found in June 1991. The disease also occurs on Leucaena leucocephala (Lam.) de Wit, which is commonly used to provide shade for cocoa and as a support for pepper. Because P. noxius infects tree stumps, then spreads by root-to-root contact (1), all stumps in an infested area must be removed before replanting is done.

Reference: (1) F. C. Henderson. Papua New Guinea Agric. J. 9:45, 1954.