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Xanthomonas campestris pv. asclepiadis, pv. nov., Causative Agent of Bacterial Blight of Milkweed (Asclepias spp.). Paula Flynn, Department of Plant Pathology, Iowa State University, Ames 50011. Anne K. Vidaver, Department of Plant Pathology, University of Nebraska, Lincoln 68583-0722. PLANT DIS. 79:1176. Accepted for publication 14 June 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-1176.

Milkweed (Asclepias spp.) is currently grown in Nebraska as an alternative crop, principally for its floss. Plants with symptoms of leaf blight were observed in commercial milkweed fields and field plots from 1987 to 1993. A yellow-pigmented, gram-negative bacterium was consistently isolated from leaves and also from infected or infested seed, steins, roots, and flowers. The pathogen was identified using polypeptide and substrate-utilization profiles, fatty acid and pigment analysis, and growth on a semiselective medium. Host range tests on members of the milkweed family and on plants representing various commercial crops grown in Nebraska showed the pathogenic specificity of the bacterium for five of six Asclepias species tested. The pathogen appears to be a new pathovar of Xanthomonas campestris. The name proposed for this bacterium is Xanthomonas campestris pv. asclepiadis.

Keyword(s): Asclepias speciosa Torr, Asclepias syriaca L