Evidence for an Expanded Host Range of Fusarium oxysporum f. sp. betae

Abstract

F. oxysporum f. sp. betae causes disease and premature death of susceptible sugar beet [Beta vulgaris] lines grown for seed in the Willamette Valley of Oregon [USA]. In some fields, pigweed (Amaranthus retroflexus) plants exhibited disease symptoms characteristic of attack by a vascular pathogen. Symptoms included 1-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 sugar beets. Cross-inoculations conducted in the greenhouse with single-spore isolates from sugar beet and pigweed demonstrated that these isolates are indistinguishable in their reaction on these hosts and both are considered to be F. oxysporum f. sp. betae. The susceptibility of pigweed appears similar to that of susceptible sugar beet lines. Field and greenhouse trials indicated that there also may be a relationship between the spinach [Spinacia oleracea] and sugar beet pathogens. The weeds Chenopodium album, Brassica nigra and wild Anethum graveolens are 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 sugar beets for the 1st time.