Influence of Soil Temperature on the Expression of Yellows and Wilt of Crucifers by Fusarium oxysporum. P. W. Bosland, Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706. P. H. Williams, and R. H. Morrison. Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706, and Plant Pathologist, Northrup King Co., Woodland, CA 95695. Plant Dis. 72:777-780. Accepted for publication 24 March 1988. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/PD-72-0777.

The effect of soil temperature (10–24 C) on disease expression by five pathotypes of Fusarium oxysporum, the incitant of yellows and wilt on crucifers, was investigated in soil temperature tanks. Various cabbage cultivars were also tested in a coastal California field naturally infested with F. o. f. sp. conglutinans race 2. For all pathotypes, virulence on their respective susceptible hosts was influenced strongly by soil temperature, with disease severity increasing as soil temperatures increased. With two pathotypes, F. o. f. sp. conglutinans race 2 and F. o. f. sp. raphani, susceptibility was observed on their respective susceptible hosts, cabbage cultivar Golden Acre and radish cultivar White Icicle, at 10 C. In cabbage, monogenic dominant (type A) resistance was highly effective against F. o. f. sp. conglutinans race 1, but was progressively less effective against F. o. f. sp. conglutinans race 2 as soil temperatures were increased from 14 to 20 C, and was ineffective at 22 and 24 C. The polygenic (type B) resistance in cabbage was highly effective against F. o. f. sp. conglutinans race 1 at 20 C and below, but was only effective against F. o. f. sp. conglutinans race 2 at 10 and 12 C. In the field test, resistance in cabbage cultivars with either type A or type B resistance was expressed under cool coastal California conditions during the summer months.