First report of phomopsis stem canker of sunflower (Helianthus annuus) caused by Diaporthe gulyae in Canada.
During September 2012, Phomopsis stem canker was observed on sunflowers (H. annuus) in a production field during seed filling with an average incidence of 15% in Morden, Manitoba, Canada. The infected plants had elongated, brown-black lesions surrounding the leaf petiole, with numerous pycnidia, pith damage, and mid-stem lodging. Based on morphological characteristics, sequence analysis of the DNA internal transcribed spacer region and pathogenicity tests, the causal agent was identified as D. gulyae. This fungus was first reported as a pathogen on H. annuus in Australia and USA in 2011. The pathogen was determined to be as or more aggressive than the other causal agents of Phomopsis stem canker, and its identification in both countries was circumstantially associated with increased incidence and yield loss in commercial production fields. In Canada, Phomopsis stem canker has been observed in sunflower fields over the last 10 years at low incidences, especially in years with above-normal temperatures during the sunflower growing season; however, the causal agent was not confirmed. This is thought to be the first report of D. gulyae causing Phomopsis stem canker on sunflowers in Canada.