Location: Sunflower and Plant Biology ResearchTitle: Phomopsis Stem Canker: A reemerging threat to sunflower (Helianthus annuus) in the United States Author
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2015
Publication Date: 7/23/2015
Citation: Mathew, F.M., Alananbeh, K.M., Jordahl, J.G., Meyer, S.M., Castlebury, L.A., Gulya, T.J., Markell, S.G. 2015. Phomopsis Stem Canker: A reemerging threat to sunflower (Helianthus annuus) in the United States. Phytopathology. 105(7): 990-997. DOI: http://dx.doi.org/10.1094/PHYTO-11-14-0336-FI. Interpretive Summary: Sunflower is an important oilseed crop in the Great Plains of the United States and elsewhere in the world. It is plagued by a number of diseases that reduced yield, including Phomopsis stem canker. This disease was assumed to be the caused by a fungus called Diaporthe helianthi. However, an analysis using very specific genetic markers indicates that the disease is also caused by D. gulyae. Both fungal organism are about equally aggressive in their infection of cultivated sunflower. Knowledge concerning the casual agents for Phomopsis stem canker is important for management of the disease.
Technical 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-a, 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.