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Disease Note.

First Report of Race 2 of Cabbage Yellows Caused by Fusarium oxysporum f. sp. conglutinans in Texas. R. H. Morrison, Sakata Seed America, Salinas, CA 93907. A. Mengistu and P. H. Williams, Deparlmenl of Plant Pathology, University of Wisconsin, Madison 53706. Plant Dis. 78:641. Accepted for publication 3 February 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0641C.

Yellows of cabbage, Brassica oleracea L. var. capitata L., is caused by races 1 and 2 of Fusarium oxysporum Schlect. f. sp. conglutinans (Wollenweb.) W.C. Snyder & H.N. Hans (2). Race 1 does litlle damage al soil temperatures below 18 C and is controlled by polygenic B resistance up to 22 C and by monogenic dominant A resistance up to 28 C. Race 2, in contrast, damages susceptible genotypes at 12 C and above and overcomes B and A resistance at temperatures above 14 and 22 C, respectively. In October 1992, cabbage plants with yellows symptoms (stunting, chlorosis, leaf drop, and vascular browning in stems and roots) were found in commercial plantings of susceptible and A-resistant cabbages in the Rio Grande Valley near Mission, Texas. Isolations consistently yielded F. oxysporum. Isolates were compared with races 1 and 2 of F. oxysporum f. sp. conglutinans on Ihe differential cabbage cultivars Golden Acre (susceptible), Rio Verde (B resistant), and Greenboy and Bravo (A resistant) with a standard root dip inoculation method (106 spores/ml) (1) at 23-24 C. All cultivars showed typical yellows symptoms and were susceptible to the Texas isolates, a response comparable to race 2. Against race 1, in contrast, Golden Acre was susceptible, Rio Verde was moderately susceptible, and Greenboy and Bravo were resistant. Consequently, the Texas isolates were typed as race 2, which has previously been identified only in California (1985) and Russia (1988). Texas is typically a cool season cabbage-growing region and has been considered at low risk for yellows. However, race 2 may pose a threat since it attacks susceptible, B-resistant, and A-resistant cultivars at lower respective soil temperatures than race 1. Late summer and early fall plantings, when soil temperatures often exceed 24 C, may be al particular risk.

References: (1) P. W. Bosland et al. Plant Dis. 72:777, 1988. (2) P. W. Bosland and P. H. Williams. Can. J. Bot 65:2067, 1986.