Comparison of Methods to Evaluate Alfalfa Cultivars for Reaction to Verticillium albo-atrum. C. R. Grau, Professor, Department of Plant Pathology, University of Wisconsin-Madison 53706. S. L. Nygaard, D. C. Arny, and P. A. Delwiche. Research Pathologist, W-L Research, Inc., Evansville, WI 53536, Emeritus Professor, Department of Plant Pathology, University of Wisconsin-Madison 53706, and Plant Pathologist, L. D. Maffaei Seed Co., Newman, CA 95360. Plant Dis. 75:82-85. Accepted for publication 29 June 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0082.

The evaluation of 34 alfalfa (Medicago sativa L.) cultivars for reaction to Verticillium albo-atrum was conducted in controlled and field environments. In controlled environments, the results of two different methods of host inoculation were compared and found to be similar. Inoculation with conidia of V. albo-atrum was accomplished by either uprooting 6-wk-old plants, clipping off their stems, and soaking the entire plant in a conidial suspension or by clipping the stems off with an infested scissors and spraying the stubble with a conidial suspension. In the field, Verticillium wilt symptom frequency and stand density were recorded for 4 yr at one location. Maximum symptom expression occurred during the spring regrowth in the third and fourth years of the stand. Maximum field disease severity was significantly correlated with results from either of the inoculation methods in controlled environments. Several cultivars expressed less disease in the field test than was predicted based on evaluations conducted in controlled environments. These cultivars may possess a type of field resistance that is not readily identified by artificial inoculation and incubation in controlled environments.