Fusarium Species Associated with Crown Rot of Alfalfa in Nevada. Wakar Uddin, Former Graduate Student, Department of Plant Science, University of Nevada, Reno 89557. Ted R. Knous, Assistant Professor of Plant Pathology, Department of Plant Science, University of Nevada, Reno 89557. Plant Dis. 75:51-56. Accepted for publication 24 June 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0051.

The distribution, pathogenicity, and phytotoxicity of Fusarium species associated with crown rot of alfalfa (Medicago sativa) was examined in 14 fields in the northern Nevada counties of Churchill, Pershing, and Lyon. The five species recovered, in descending order of frequency, were F. solani, F. acuminatum, F. oxysporum, F. sambucinum, and F. avenaceum. Only F. sambucinum and F. avenaceum were not isolated at all locations. Isolates of F. solani and F. acuminatum were the most pathogenic on 4-mo-old alfalfa, followed by F. sambucinum and F. oxysporum. An isolate of F. avenaceum was the least pathogenic. However, there were interactions between the Fusarium species and the alfalfa cultivars. Pathogenicity and the frequency of recovery were positively correlated. Synergism was observed when all five species were present. Cell-free culture filtrates of F. sambucinum and F. acuminatum caused local and translocatable phytotoxicity in an alfalfa leaf bioassay, while filtrates of the other three species did not. There were no significant differences among eight alfalfa cultivars in the phytotoxic reaction caused by the culture filtrates of these Fusarium species.