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

Authors: Bourret, Tyler; BLOMQUIST, CHERYL - California Department Of Food And Agriculture; MOHAN, KRISHNA - University Of Idaho; SAMPANGI, RAM - University Of Idaho; HO, HON - State University Of New York (SUNY); MOHAMMED, ISRAFIEL - California Department Of Food And Agriculture

Submitted to: PhytoFrontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/13/2024
Publication Date: 10/23/2024
Citation: Bourret, T.B., Blomquist, C.L., Mohan, K.S., Sampangi, R., Ho, H.H., Mohammed, I.A. 2024. 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 . PhytoFrontiers. 2690-5442. https://doi.org/10.1094/PHYTOFR-02-24-0013-R.
DOI: https://doi.org/10.1094/PHYTOFR-02-24-0013-R

Interpretive Summary: Phytophthora is a genus of plant pathogens that pose grave threats to plants growing in agriculture, horticulture and natural ecosystems. A disease on yellow nutsedge (Cyperus esculentus) growing near irrigated onion fields was observed beginning in July 1996 in Idaho and Oregon. Plant symptoms included necrotic spots and blotches, and blighting of above-ground tissue. Morphological and molecular techniques were used to characterize the pathogen. Phytophthora cyperi was identified as the causal agent and pathogenicity was confirmed by inoculating healthy nutsedge plants with zoospores from infected plants. This information will be used by plant pathologists, regulatory officials and others involved in plant disease management to identify this pathogen and track its movement both geographically and by host.

Technical 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, 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 ELISA kit and all efforts to culture the organism on semi-selective or general fungal media failed. 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 a ~1300 bp insertion.