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Effects of Water Stress on Thyronectria Canker of Honeylocusts. W. R. Jacobi, Associate professor, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523; J. W. Riffle, former research plant pathologist, USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Forestry Sciences Laboratory, University of Nebraska, Lincoln 68583. Phytopathology 79:1333-1337. Accepted for publication 3 July 1989. 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-79-1333.

Drought-stressed 1- to 3-yr-old honeylocust trees (Gleditsia triacanthos) developed significantly (P = 0.05) smaller Thyronectria cankers (Thyronectria austro-americana) than well-watered seedlings, as measured by bark canker size. Analysis of variance of vertical canker size and percent girdling indicated significant interactions of linear trends across time with isolate and stress factors. Xylem (staining and colonization) canker size was not affected by the stress treatment. Pressure bomb assessment of the trees’ water potentials was well correlated with both bark and xylem canker sizes up to 30 days after inoculation. Bark cankers expanded more above the inoculation wound than below. More stromatic conidiomata formed on nonstressed trees than stressed trees. In vitro growth of T. austro-americana was reduced significantly (P = 0.05) with increasing amounts of polyethylene glycol in the media, suggesting that pathogen growth is slower at low osmotic potentials. Thus, the smaller cankers on drought-stressed trees may result partly from reduced growth of the pathogen.