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Etiology

Evidence for an Expanded Host Range of Fusarium oxysporum f. sp. betae. J. D. MacDonald, Graduate Research Assistant, Department of Plant Pathology, University of California, Davis 95616; L. D. Leach, Professor Emeritus, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 66:822-827. Accepted for publication 13 January 1976. DOI: 10.1094/Phyto-66-822.

Fusarium oxysporum f. sp. betae causes disease and premature death of susceptible sugarbeet lines grown for seed in the Willamette Valley of Oregon. In some fields, pigweed (Amaranthus retroflexus) plants exhibited disease symptoms characteristic of attack by a vascular pathogen. Symptoms included one-sided wilt, vascular discoloration, and death of plants. Cultures from diseased pigweed plants yielded isolates of F. oxysporum morphologically identical to those obtained from blighted sugarbeets. Cross-inoculations conducted in the greenhouse with single-spore isolates from sugarbeet and pigweed have demonstrated that these isolates are indistinguishable in their reaction on these hosts and both therefore are considered to be F. oxysporum f. sp. betae. The susceptibility of pigweed appears similar to that of susceptible sugarbeet lines. Field and greenhouse trials have indicated and that there also may be a relationship between the spinach and sugarbeet pathogens. The weeds Chenopodium album, Brassica nigra, and wild Anethum graveolens have been identified as symptomless carriers of the stalk blight pathogen. These susceptible and symptomless hosts could provide an explanation for the frequent occurrence of stalk blight in Oregon fields cropped with sugarbeets for the first time.