Pathogenicity and Virulence of Phytophthora capsici Isolates from Taiwan on Tomatoes and Other Selected Hosts. G. L. Hartman, Research Plant Pathologist, Agriculture Research Service, U.S. Department of Agriculture, and Department of Plant Pathology, University of Illinois, Urbana 61801. Y. H. Huang, Research Assistant, Asian Vegetable Research and Development Center, P.O. Box 42, Shanhua, Tainan, Taiwan 74199, Republic of China. Plant Dis. 77:588-591. Accepted for publication 17 February 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/PD-77-0588.

In container experiments, black nightshade, cabbage, cucumber, pepper, potato, tobacco, and tomato plants were inoculated with isolates of Phytophthora capsici obtained from either pepper stems or tomato foliage. Inoculum was applied by atomizing foliage or by drenching soil with zoospore suspensions of 1 × 10⁴ zoospores per milliliter. Foliage and stem blight developed on black nightshade, pepper, and tomato plants but not on the other plant species. Tomato and pepper seedlings were inoculated with five isolates of P. capsici by spraying foliage or drenching soil. Response to individual isolates varied from no symptoms to 100% blighting and death of foliar-inoculated pepper plants. Regardless of isolate, basal stem blight was not observed on soil-inoculated tomato plants, whereas reaction of pepper plants varied from no symptoms to severe crown lesions causing death. Seedlings of 11 tomato lines foliar-inoculated with one isolate were all susceptible, although the amount of foliage blighted differed among lines. Detached tomato leaves inoculated with a zoospore suspension had more blight at 24 and 28 C than at higher and lower temperatures 3 days after inoculation. In the field, two foliar-inoculated tomato lines developed leaf blight by 3 days after inoculation, and by 14 days, 45–60% of the leaf area was blighted.