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Etiology

Interaction of Fusarium avenaceum and Pseudomonas viridiflava in Root Rot of Red Clover. K. T. Leath, U.S. Regional Pasture Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, University Park, PA 16802; F. L. Lukezic(2), B. W. Pennypacker(3), W. A. Kendall(4), R. G. Levine(5), and R. R. Hill, Jr.(6). (2)(3)(5)Department of Plant Pathology, The Pennsylvania State University, University Park 16802; (4)(6)U.S. Regional Pasture Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, University Park, PA 16802. Phytopathology 79:436-440. Accepted for publication 5 November 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-79-436.

Fusarium avenaceum and Pseudomonas viridiflava were inoculated separately or together into roots of red clover to determine if these pathogens interacted synergistically to cause more severe disease symptoms. When these pathogens were inoculated together into wounded roots of 4-wk-old plants grown gnotobiotically, they caused significantly longer rot lesions and more severe disease symptoms than when inoculated separately. Samples for microscopic examination were produced by the inoculation of 8-wk-old plants grown hydroponically on slant boards. Inoculations were made by introducing inoculum suspensions into severed lateral roots about 1.5 cm below the crowns. Examination of cross sections, made through the taproot at the juncture with the inoculated lateral root, showed that only minor tissue damage was caused by either organism inoculated alone, and that damage was confined mainly to the inoculated lateral root. Inoculation with both pathogens together resulted in the destruction of periderm, secondary phloem, vascular cambium, xylem parenchyma, xylem fibers, and some xylem vessels in the taproot. The organisms were intercellular and intracellular in the areas of severe tissue disruption. Histological evidence and in vitro tests indicated that the combined organisms degraded cellulose more extensively than could be expected from the individual organisms.