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The Role of Bacteria in the Root and Crown Rot Complex of Irrigated Sainfoin in Montana. Denis A. Gaudet, Former research assistant, Montana State University, Bozeman 59717, Present address of senior author: Department of Plant Pathology, North Dakota State University, Fargo 58102; D. C. Sands(2), D. E. Mathre(3), and R. L. Ditterline(4). (2)(3)(4)Assistant professor, and professor of Plant Pathology, and associate professor of Agronomy, respectively, Montana State University, Bozeman 59717. Phytopathology 70:161-167. Accepted for publication 4 September 1979. Copyright 1980 The American Phytopathological Society. DOI: 10.1094/Phyto-70-161.

Root and crown rot limits stand longevity and forage yield in sainfoin grown in Montana. A histological investigation of decayed sainfoin roots revealed the presence of bacterial cells within discolored vessels and decayed cavities in the root xylem. The bacteria were closely associated with tissue degeneration in naturally infected 3- and 4-yr-old sainfoin roots. Four different bacteria consistently were isolated from 2-, 3-, and 5-yr-old naturally infected sainfoin roots with typical symptoms. Three of these bacteria produced typical symptoms of root and/or crown rot when reinoculated into greenhouse-grown sainfoin. The three bacteria, Pseudomonas syringae, P. marginalis (P. fluorescens), and an Erwinia amylovora-like bacterium, were equally capable of producing symptoms in the inoculated plants. Fusarium solani, previously considered the causal organism of root and crown rot of sainfoin, was not consistently isolated from symptomatic tissues. Consequently, the causal organisms involved in the root and crown deterioration in irrigated sainfoin may be one or more bacteria rather than a single fungal pathogen.

Additional keywords: Onobrychis viciaefolia.