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Disease Note.

First Report of Soybean Rust in Hawaii. E. Killgore, Plant Pest Control Branch, Hawaii State Department of Agriculture, Honolulu 96814. R. Heu, Plant Pest Control Branch, Hawaii State Department of Agriculture, Honolulu 96814, and D. E. Gardner, National Biological Survey, Department of Botany, University of Hawaii at Manoa, Honolulu 96822. Plant Dis. 78:1216. Accepted for publication 21 September 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1216B.

Soybean (Glycine max (L.) Merr.) is commonly cultivated in Hawaii and is increasingly important in attempts to diversify agriculture. In May 1994, soybean plants under cultivation in a 0.2 ha field at Mililani, in central Oahu, were found to be severely infected with a soybean rust. Rust pustules occurred on 100% of plants accompanied by chlorosis, necrosis, and defoliation with no salvageable crop. Fields with infected plants were subsequently found in Waimanalo (100% infection) and Kahaluu (80% infection) on the windward side of Oahu, with neighboring fields apparently rust free. In July 1994, moderate infection (10-20% of plants) was found in a field near Kakaha, Kauai, and 80% infection occurred near Hilo, Hawaii. Information on the cultivars or seed source was not available in each case. Many weed hosts of soybean rust are known within the Fabaceae which may serve as noncrop reservoirs of the pathogen (1), but of these only Crotalaria incana L. has been found to be infected in Hawaii. Infection on this host on Oahu was light (a few pustules on <10% of plants observed). Only the uredinial state of the rust has been found in Hawaii, material of which has been confirmed by Dr. Joe Hennen (personal communication) and deposited in the Arthur Herbarium (PUR 89900, 89901). The spores are pale cinnamon-brown, uniformly and finely echinulate, wall uniformly about 1 Μm thick, germ pores obscure, spores sessile, obovoid to broadly ellipsoid, 16-24 x 24-31 Μm. Paraphy-ses are numerous, pale yellow, straight or incurved with thin sidewalls and a prominent apical thickening up to 10 Μm thick. Sori are hypophyllous with spores expelled through a prominent central pore. Rust on soybeans has been until recently referred to a single species: Phakopsora pachyrhizi H. & P. Sydow. However, a second species, P. meibomiae (Arthur) Arthur, also is known to incite soybean rust disease (1). The uredinial states of these fungi, which cannot reliably be distinguished from one another morphologically, have been described as the anamorphic species Malupa sojae (P. Hennings) Ono, Buritica, & Hennen for P. pachyrhizi, thought to originate in Asia and to be the more virulent of the two on soybean, and M. vignae (Bresadola) Ono, Buritica, & Hennen for P. meibomiae, thought to originate in the Americas and to be the less virulent (1). P. pachyrhizi (or M. sojae) has not yet been confirmed on the North or South American continents and introduction would be of tremendous economic significance (1). Hawaii's position as a stepping stone between the eastern and western hemispheres and the high volume of air traffic between Hawaii and North America enhance this threat, to which soybean producers should be alerted.

Reference: (1) Y. Ono et al. Mycol. Res. 96:825, 1992.