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Abstract
Water spinach, a specialty vegetable and a member of the sweet potato family, is cultivated for Asian markets in California (United States) and Ontario (Canada). Foliar diseases of this vegetable observed in commercial greenhouses of Ontario in 1993 and 1994, as well as in greenhouses of California in 1998, were attributed respectively to Phyllosticta ipomoeae, Cercospora ipomoeae, and Pseudomonas syringae pv. syringae in the present study. In Ontario, C. ipomoeae infected less than 1% of plants, with less than 25% of the foliage affected, while Phyllosticta ipomoeae occurred on 100% of plants in some greenhouses, with leaf spotting affecting up to 25% of the foliage. In California, Pseudomonas syringae pv. syringae occurred on less than 25% of plants with up to 25% of the foliage affected. In Ontario, no virus was detected in eight suspect foliage samples while damage from vectors of plant viruses such as the green peach aphid (Myzus persicae) was minor and from Western flower thrips (Frankliniella occidentalis) was moderate. Edema affected water spinach at four sites in Ontario in 1994, with both the incidence and severity exceeding 75% at one site. For fungal and bacterial pathogens, Koch's postulates were fulfilled by inoculation and reisolation. Morphological characteristics of isolates in vitro and in vivo were used to identify the fungal pathogens, and LOPAT tests and fatty acid analyses were applied to identify the bacterial pathogen. Symptoms and etiology are discussed. This is the first report of these diseases, pests, and abiotic disorders on water spinach in Ontario and California.
