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Disease Note.

First Report of Calonectria colhounii Causing Blight of Leucospermum in Hawaii. J. Y. Uchida, Department of Plant Pathology, University of Hawaii, Honolulu 96822. C. Y. Kadooka, S. Ferreira, and N. Nagata, Department of Plant Pathology, University of Hawaii, Honolulu 96822. Plant Dis. 80:103,. Accepted for publication 14 November 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0103C.

Leucospermum cordifolium (J. Knight) Foure., L. conocarpodendron (L.) Buek, and other species of this genus, commonly known as pincushion, are widely grown in Hawaii for floral export. Tan to brown leaf spots associated with a Cylindrocladium species were found on plants on the island of Hawaii. Single conidial cultures of three Cylindrocladium isolates were established from diseased plants and maintained on V8 juice agar (VJA). Most morphological studies were made on VJA, and perithecia were produced on autoclaved Howeia leaves placed on water agar. For pathogenicity studies, conidia were produced on VJA at 240C with light, collected, suspended in water, and adjusted to 104 spores/ml. Cuttings of an interspecific hybrid of commercial Leucospermum species, selection #31, developed by the University of Hawaii, were rooted and planted in Sunshine Blend No. 4 peat mix. Leaves were sprayed to run-off and plants were incubated at 100% relative humidity for 24 h and returned to the glasshouse (20 to 400C). Roots of other plants were inoculated by drenching with 2.5 x 106 conidia per 400 cc of peat mix. Three clays following inoculation all foliar inoculated plants were symptomatic. Young leaves were blighted while older leaves had numerous flecks. Blighted areas and spots 30 to 65 mm long by 8 to 15 mm wide were typically tan to light brown. Stem lesions were small (3 to 4 min) spots with brown centers, green borders, and a diffuse reddish zone. Loss of apical leaves was followed by the production of new shoots plants were not killed. Roots appeared to be tolerant of the fungus and root-inoculated plants remained healthy for at least 4 months following inoculation. Pathogenicity tests were repeated at least once and the pathogen was reisolated from leaves but not stems or roots. Based on conidial dimensions, stipe length, clavate vesicle, and yellow perithecia with asci each having four ascospores, the pathogen was identified as Calonectria colhounii Peerally (anamorph = Cylindrocladium colhounii). This is the first report of this disease in Hawaii. This fungus has also been isolated from Howeia (1), Metrosideros, Eucalyptus, and Chrysalidocarpus. This disease report, as well as others of ornamental and foliage hosts, suggests that Calonectria is a major pathogen in the tropics.

Reference: (1) J. Y. Uchida and M. Aragaki. Plant Dis. 76:853, 1992.