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Crown Rot of Eustoma Caused by Fusarium avenaceum in California. S. T. Koike, University of California Cooperative Extension, Salinas 93901 . T. R. Gordon, Department of Plant Pathology, University of California, Davis 95616; and S. E. Lindow, Department of Plant and Microbial Biology, University of California, Berkeley 94720. Plant Dis. 80: 1429. Accepted for publication 3 October 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1429B.

From 1994 to 1996, symptoms of a previously undescribed disease were observed on greenhouse-planted Eustoma (Eustoma grandiflorum (Raf.) Shinn. = Lisianthus russellianus Hook), grown in coastal Monterey County for cut flowers. Symptomatic plants appeared water-stressed and dull green in color. Leaves and growing tips wilted and eventually collapsed. Plant crowns and lower stems were rotted, with the decay extending 10 to 15 cm above the ground. Leaves attached at the crowns and lower stems became light tan, as did the stems. White mycelia and orange sporodochia were commonly observed on diseased crowns and stems, from which a Fusarium sp. was consistently recovered on acidified potato dextrose agar. Single-spore subcultures of four representative isolates were grown under fluorescent lights on carnation leaf agar. All isolates produced abundant macroconidia in sporodochia on carnation leaf pieces. Macroconidia were slender and gently curved with a notched basal cell and an elongate, sometimes bent, apical cell. Chlamydospores were absent. Microconidia were sparse in two isolates and apparently absent in the other two. All isolates were positive for ice-nucleating activity (1). Based on these criteria, all isolates were identified as F. avenaceum (Fr: Fr.) Sacc. Pathogenicity was demonstrated on 10- to 12-week-old E. grandiflorum cv. Soyokaze plants inoculated at the crowns with colonized agar plugs or drops of a 150,000 conidia per ml suspension. Control plants received sterile agar plugs or drops of sterile, distilled water. All plants were maintained in a greenhouse. After 18 to 21 days, inoculated plants developed crown decay symptoms similar to those initially observed, and F. avenaceum was reisolated from crown tissue. Control plants remained symptomless. The two inoculation methods were conducted three times each, with similar results each time. This is the first report of a crown rot disease of Eustoma caused by F. avenaceum.

Reference: (1)S. Pouleur et al. Appl. Environ. Microbiol. 58:2960, 1992.