title: Phomopsis Stem Canker: A Reemerging Threat to Sunflower (Helianthus annuus) in the United States.
abstract: Phomopsis stem canker causes yield reductions on sunflower (Helianthus annuus L.) on several continents, including Australia, Europe, and North America. In the United States, Phomopsis stem canker incidence has increased 16-fold in the Northern Great Plains between 2001 and 2012. Although Diaporthe helianthi was assumed to be the sole causal agent in the United States, a newly described species, D. gulyae, was found to be the primary cause of Phomopsis stem canker in Australia. To determine the identity of Diaporthe spp. causing Phomopsis stem canker in the Northern Great Plains, 275 infected stems were collected between 2010 and 2012. Phylogenetic analyses of sequences of the ribosomal DNA internal transcribed spacer region, elongation factor subunit 1-α, and actin gene regions of representative isolates, in comparison with those of type specimens, confirmed two species (D. helianthi and D. gulyae) in the United States. Differences in aggressiveness between the two species were determined using the stem-wound method in the greenhouse; overall, D. helianthi and D. gulyae did not vary significantly (P≤0.05) in their aggressiveness at 10 and 14 days after inoculation. These findings indicate that both Diaporthe spp. have emerged as sunflower pathogens in the United States, and have implications on the management of this disease.
authors.affiliation: First, second, third, fourth, and seventh authors: Department of Plant Pathology, North Dakota State University, Fargo 58102-6050; fifth author: United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Systematic Mycology and Microbiology Lab, Beltsville, MD 20705; sixth author (retired): USDA-ARS Northern Crop Science Laboratory, Fargo, ND 58108.
authors.forename: Febina M
authors.initials: FM
authors.lastname: Mathew
authors.affiliation: First, second, third, fourth, and seventh authors: Department of Plant Pathology, North Dakota State University, Fargo 58102-6050; fifth author: United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Systematic Mycology and Microbiology Lab, Beltsville, MD 20705; sixth author (retired): USDA-ARS Northern Crop Science Laboratory, Fargo, ND 58108.
authors.forename: Kholoud M
authors.initials: KM
authors.lastname: Alananbeh
authors.affiliation: First, second, third, fourth, and seventh authors: Department of Plant Pathology, North Dakota State University, Fargo 58102-6050; fifth author: United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Systematic Mycology and Microbiology Lab, Beltsville, MD 20705; sixth author (retired): USDA-ARS Northern Crop Science Laboratory, Fargo, ND 58108.
authors.forename: James G
authors.initials: JG
authors.lastname: Jordahl
authors.affiliation: First, second, third, fourth, and seventh authors: Department of Plant Pathology, North Dakota State University, Fargo 58102-6050; fifth author: United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Systematic Mycology and Microbiology Lab, Beltsville, MD 20705; sixth author (retired): USDA-ARS Northern Crop Science Laboratory, Fargo, ND 58108.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Meyer
authors.affiliation: First, second, third, fourth, and seventh authors: Department of Plant Pathology, North Dakota State University, Fargo 58102-6050; fifth author: United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Systematic Mycology and Microbiology Lab, Beltsville, MD 20705; sixth author (retired): USDA-ARS Northern Crop Science Laboratory, Fargo, ND 58108.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Castlebury
authors.affiliation: First, second, third, fourth, and seventh authors: Department of Plant Pathology, North Dakota State University, Fargo 58102-6050; fifth author: United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Systematic Mycology and Microbiology Lab, Beltsville, MD 20705; sixth author (retired): USDA-ARS Northern Crop Science Laboratory, Fargo, ND 58108.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Gulya
authors.affiliation: First, second, third, fourth, and seventh authors: Department of Plant Pathology, North Dakota State University, Fargo 58102-6050; fifth author: United States Department of Agriculture-Agricultural Research Service (USDA-ARS) Systematic Mycology and Microbiology Lab, Beltsville, MD 20705; sixth author (retired): USDA-ARS Northern Crop Science Laboratory, Fargo, ND 58108.
authors.forename: Samuel G
authors.initials: SG
authors.lastname: Markell
mesh_terms: D001203:Ascomycota / Q000235:genetics* / Q000472:pathogenicity; D006368:Helianthus / Q000382:microbiology*; D054884:Host-Pathogen Interactions; D010802:Phylogeny; D010935:Plant Diseases; D014481:United States
keywords: pathogenicity