First Report of Phytophthora palmivora Causing Aerial Blight on Physocarpus opulifolius ‘Summer Wine’ at a Wholesale Nursery in Virginia

Abstract

On 8 August 2023, at a wholesale nursery in Nelson County, Virginia, approximately 500 Physocarpus opulifolius ‘summer wine’ plants in 11.4-liter containers were observed with leaf necrosis, shepherd's crook, and stem cankers. The isolates recovered from diseased tissue were identified as Phytophthora palmivora based on morphological and molecular analysis. A 778-bp segment of the internal transcribed spacer locus and 827-bp segment of the cytochrome c oxidase subunit 1 locus from isolate AE03 were deposited into the GenBank database under accessions OR754361 and OR760058, respectively. Koch's postulates were fulfilled by spraying a zoospore suspension on three healthy plants and incubating them in a chamber with over 90% humidity at 22 ± 2°C. After 72 h, all three inoculated plants displayed necrotic leaf and stem lesions, and approximately 25% of the leaves senesced. To the authors’ knowledge, this is the first documentation of Phytophthora palmivora causing aerial blight on plants in the genus Physocarpus.