Disease Note

Greasy Leaf Blotch of Dendrobium nobile Caused by Aphelenchoides besseyi. W. T. Nishijima, Department of Plant Pathology, University of Hawaii, Honolulu 96822. O. V. Holtzmann, Department of Plant Pathology, University of Hawaii, Honolulu 96822. Plant Dis. 68:826. Accepted for publication 18 June 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-826e.

A leaf blotch disease of the orchid Dendrobium nobile Lindl. was observed in a commercial greenhouse in Mountain View, Hawaii. The foliar nematode Aphelenchoides besseyi Christie was extracted and identified from infected leaves. Initial symptoms were irregular lesions characterized by dark, greasy, hydrotic areas that were often vein- limited. Chlorosis, necrosis, and leaf drop occurred in advanced stages. The abaxial surface of succulent, immature leaves on 30-cm-tall plants were inoculated without wounding with A. besseyi (1,00O/leaf) and incubated in a moisture chamber for 48 hr. Typical lesions developed in 75 days, with an abundance of foliar nematodes in the darkened margins of the spots. High plant densities and frequent overhead sprinkler irrigations are suspected key factors in disease development.