VIEW ARTICLE

Resistance

Field Reaction of Artificially Inoculated Alfalfa Populations to the Fusarium and Bacterial Wilt Pathogens Alone and in Combination. F. I. Frosheiser, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108; D. K. Barnes, Research Plant Geneticist, Agricultural Research Service, Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108. Phytopathology 68:943-946. Accepted for publication 23 November 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-943.

Plants of 12 alfalfa cultivars and experimental lines were inoculated with Fusarium oxysporum f. sp. medicaginis and Corynebacterium insidiosum alone and in combination and then transplanted into the field. Differences in reaction to F. oxysporum and C. insidiosum were observed among the entries. The internal root symptoms of Fusarium and bacterial wilts could be differentiated by the color and outline of the discolored areas in cross section. Fusarium wilt severity was about equal in plants inoculated with F. oxysporum alone and with the mixed inoculum. Bacterial wilt was less severe when inoculated with the mixed inoculum than with C. insidiosum alone. Resistance in a cultivar to bacterial wilt, Phytophthora root rot (caused by Phytophthora megasperma), or anthracnose (caused by Colletotrichum trifolii) had no apparent effect on the development of Fusarium wilt. The procedure described for inoculation and culture of the alfalfa plants appeared satisfactory for evaluating their reaction to F. oxysporum and for screening alfalfa populations for resistance to the pathogen.