First Detection of the Obligate Biotroph Phytophthora cyperi Causing Disease on Yellow Nutsedge in the United States, and Establishment of Molecular Barcoding Sequences for the Species

Abstract

A pathogen causing disease on yellow nutsedge (Cyperus esculentus) growing in and near irrigated areas of onion seed and bulb fields in Idaho and Oregon during July and August 1996 was morphologically and molecularly characterized. Plant symptoms included necrotic spots and blotches and blighting of leaves, stems (culms), and bracts. Symptomatic tissue contained glistening white masses of mycelium and oval semi-papillate sporangia emerging from stomata on sporangiophores. Later, subspherical oogonia with smooth oospores were found embedded in older infected tissue. Phytophthora cyperi was identified as the causal agent, and pathogenicity was confirmed by inoculating healthy nutsedge plants with sporangia from infected plants. Infected samples tested negative using Agdia's Phytophthora enzyme-linked immunosorbent assay (ELISA) kit, and all efforts to culture the organism on semi-selective or general fungal media failed. To aid future efforts to detect this species, sequences of the two primary barcoding loci, ITS rDNA and mitochondrial cox1, were obtained from the organism and analyzed, finding an unexpectedly large ITS sequence characterized by an approximately 1,300-bp insertion. [Figure: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Keywords

• cox1
• Cyperus esculentus
• downy mildews
• intron
• ITS
• oogonia