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Variability in Septoria musiva in Aggressiveness. J. M. Krupinsky, Plant pathologist, Northern Great Plains Research Laboratory, Agriculture Research Service, U.S. Department of Agriculture, P.O. Box 459, Mandan, ND 58554; Phytopathology 79:413-416. Accepted for publication 19 October 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1989. DOI: 10.1094/Phyto-79-413.

In growth studies on five different culture media, spore production of Septoria musiva was best on V-8 juice with phytone peptone agar and yeast malt extract agar. A spore concentration of 1 106 spores/ml and an incubation time of 48 hr were found to promote good symptom development in glasshouse inoculations. Different levels of aggressiveness were detected for S. musiva in glasshouse inoculations of five Populus clones with local leaf isolates, local canker isolates, and regional leaf isolates from North Dakota, South Dakota, and Minnesota. Isolates with high and low levels of aggressiveness were selected from the local leaf isolates, the local canker isolates, and the regional leaf isolates and compared. High and low levels of aggressiveness were confirmed for the three types of isolates. Canker isolates were found to be as aggressive as leaf isolates. The local leaf and local canker isolates were found to be as aggressive as isolates that were obtained from a more widespread geographic area.