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Etiology

Bacterial Vascular Necrosis and Rot of Sugarbeet: General Description and Etiology. S. V. Thomson, Assistant Professor, Department of Plant Pathology, University of California, Berkeley, CA 94720; M. N. Schroth(2), F. J. Hills(3), E. D. Whitney(4) and D. C. Hildebrand(5). (2)Professor, Department of Plant Pathology, University of California, Berkeley CA 94720; (3)Extension Agronomist, University of California, Davis, CA 95616; (4)Research Plant Pathologist, Agricultural Research Station, Salinas, CA 93901; and (5)Associate Research Plant Pathologist, University of California, Berkeley, CA 94720. Phytopathology 67:1183-1189. Accepted for publication 19 April 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1183.

Vascular necrosis and rot of sugarbeet in California is caused by specific strains of the Erwinia carotovora group of soft-rotting pathogens which can be distinguished from members of the group on the basis of host reaction and biochemical tests. The bacteria invade the vascular tissue of the petiole and roots and usually cause an extensive rot. Vascular bundles of infected roots are necrotic and areas surrounding the infected bundles turn pink upon exposure to air. The disease is found in most California sugarbeet plantings. The incidence of infection is usually 3-5%, but sometimes occurs in excess of 40%. Injury is necessary for infection, and temperatures of 25-30 C favor rapid disease development. Root yield was reduced from 76.8 metric tonnes/hectare (ha) in control plots to 37.9 metric tonnes/ha in plots where plants were injured and inoculated when 8 wk old. Infections which occur early in the season are more important since the reduction in root and sugar yield was significantly greater when 8-wk-old plants were inoculated in the field than when 12 or 15-wk-old plants were inoculated. The pathogen also infected tomato and chrysanthemum plants in greenhouse inoculations and caused typical blackleg symptoms on potatoes grown at 18 C. Some strains of Erwinia carotovora var. atroseptica, Erwinia carotovora var. carotovora, and Erwinia chrysanthemi also infected sugarbeet. A few strains of the latter two species caused blackleg of potatoes in greenhouse tests at 18 C. Populations of the sugarbeet Erwinia sp. in soils planted to sugarbeets ranged from 2.1 × 10² to 2.8 × 10⁶ colony-forming units/g of soil. Populations declined rapidly after harvest and the organism was not detected in soils throughout the winter. The Erwinia sp. was not isolated from sugarbeet seed.