Disease Note.

First Report of Pigeon Pea Root Rot Caused by Phellinus noxius in Papua New Guinea.. J. J.C. Dennis, PNG Cocoa & Coconut Research Institute, P.O. Box 1846, Rabaul, Papua New Guinea. Plant Dis. 78:316. Accepted for publication 27 October 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0316B.

In April 1992, 20% of 1 ha of 18-mo-old pigeon pea plants (Cajanus cajan (L.) Huth) growing in an area previously planted with cocoa (Theobroma cacao L.) died as the result of root infections by Phellinus noxius (Corner) G. Cunn. The first symptom observed on the pigeon peas was reduced vigor, followed quickly by yellowing and wilting of leaves, and then sudden death, all within 3 to 4 wk. A brown-black fungal crust was present on the surface of the stem at ground level, and a soil-encrusted fungal sleeve covered the surface of the roots. This disease has been reported on pigeon pea in Nigeria (1). Using cocoa seedlings to isolate the pathogen, Koch’s postulates were successfully tested to verify the causal pathogen as P. noxius. A 10-cm length of infected pigeon pea root, 2-cm diameter, was placed beneath the soil adjacent to the stem of 3-mo-old cocoa seedlings. Symptoms of leaf browning and formation of a brown-black fungal crust at the base of the cocoa stem appeared within 6 mo of inoculation. This disease can result in significant losses of mature cocoa, and symptoms on infected pigeon peas were similar to those of infected cocoa (2). Although old cocoa stumps were cleared from this area before planting, pieces of infected roots remained, and these were found associated with the infected pigeon peas. Because P. noxius infects tree stumps and then spreads by root-to-root contact (2), this finding emphasizes the need not only to disinfect or remove all stumps before replanting an infested area but also to remove as many of the infected roots as possible. This is the first report of pigeon pea root rot caused by P. noxius in Papua New Guinea.