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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. |