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Disease Note.

First Report of Alternaria helianthi on Sunflower in Canada. W. E. Sackston, Department of Plant Science, Macdonald College of McGill University, Ste. Anne de Bellevue, Que., Canada H9X 1C0. . Plant Dis. 72:801. Accepted for publication 18 April 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0801E.

Sunflower (Helianthus annuus L.) leaves with atypical lesions of Septoria leaf spot (Septoria helianthi Ell. & Kell.) collected in a field near Arthur, Ont., in September 1987 were stored in a plastic bag at 4 C and examined 10 days later. A few spores of Alternaria helianthi (Hansf.) Tubaki & Nishihara were observed among masses of S. helianthi spores. Because of its very short latent period, A. helianthi was isolated readily by spraying a suspension of spores from the stored leaves onto young sunflower plants (cv. Peredovik), maintaining them at 100% relative humidity and 22/18 C day/night temperature, harvesting spores from the typical small brown spots that developed in 2-3 days, and repeating the process. This is the first reported occurrence of A. helianthi in Canada. S. helianthi and A. helianthi can be seed borne. As the seed for all the sunflower fields in the Arthur area came from the north central United States, where A. helianthi is present (I), it may have been introduced with the seed or debris. Temperature and humidity conditions in southern Ontario can be favorable for A. helianthi, which can cause a destructive leaf and stem disease.

Reference: (I) M. L. Carson. Phytopathology 75:1151,1985.