Disease Note

Halo Blight (Pseudomonas syringae pv. coronafaciens) on Grasses in Interior Alaska. J. H. McBeath and M. Adelman, Agricultural and Forestry Experiment Station, University of Alaska, Fairbanks 99701.  Plant Disease 70:801, 1986.  Accepted for publication 16 April 1986.  Copyright 1986 The American Phytopathological Society. DOI: 10.1094/PD-70-801f.

Severe leaf blight was observed on smooth bromegrass (Bromus inermis Leyss.) in Fairbanks and Delta-Clearwater areas of Alaska during the summer of 1985.  Similar symptoms were also observed on Kentucky bluegrass (Poa pratensis L.) and bluejoint (Calamagrostis canadensis (Michx.) Beauv.), a grass species indigenous to Alaska.  After prolonged cool, rainy weather in June, large numbers of small, purplish brown lesions appeared on the leaf blades and sheaths of the grasses.  The lesions increased in size and many were surrounded by a bright yellow halo.  A fluorescent gram-negative oxidase-negative arginine-dihydrolase-negative pseudomonad was consistently recovered on King's medium B (KMB) agar from lesions on diseased plants of all three grass species.  The bacterium was identified as Pseudomonas syringae pv. coronafaciens (Elliott) Young et al. by colony morphology on KMB and by physiological-biochemical tests.  Pathogenicity was confirmed on greenhouse tests.  This is the first report of halo blight on Alaska native grasses and the first recording of a pathogenic pseudomonad on any plant in Alaska.

References: B. M. Cunfer and N. M. Schaad. Plant Dis. Rep. 60:61, 1976.  C. S. Reddy and J. Godkin. Phytopathology 13:75, 1923.