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Ecology and Epidemiology

Endemic and Soilborne Nature of Erwinia carotovora var. atroseptica, a Pathogen of Mature Sugar Beets. Margarida de Mendonça, Graduate research associate, Department of Plant Pathology, University of Arizona, Tucson 85721; M. E. Stanghellini, professor, Department of Plant Pathology, University of Arizona, Tucson 85721. Phytopathology 69:1096-1099. Accepted for publication 10 April 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-1096.

Investigations of the endemic and soilborne nature of Erwinia carotovora var. atroseptica (biotype KSB, hereafter called “KSB”), a pathogen of mature sugar beets, were conducted in the Sulphur Springs Valley (in Arizona) after the occurrence of root rot in July, 1975. The sugar beet field was plowed in October, 1975, fallowed until March, 1976, planted to wheat in April, harvested in August, and subsequently fallowed. Rhizosphere soil from wheat and various weed plants was collected monthly from April to August, 1976, and assayed for the presence of KSB. Soil and rhizosphere isolates were identified by serological, biochemical, physiological, and pathogenicity tests. KSB was recovered from the rhizosphere of wheat, various weed, and volunteer sugar beet plants throughout the sampling period. KSB also was recovered from the rhizosphere of a native plant, Lupinus blumerii, which was collected in the Chiricahua Mountains, a natural watershed of the Sulphur Springs Valley. During a 4-mo period, biotype KSB also was recovered from the rhizosphere of artificially infested sugar beets. Over time, KSB exhibited a distinct vertical distribution in field soil; it consistently survived at soil depths greater than 12 cm. The role of temperature and soil matric water potentials on survival of KSB was investigated in laboratory tests of naturally infested soils. Populations of KSB declined only slowly over a 135-day incubation period at 0 and 10 C, and persisted only briefly under dry soil conditions or fluctuating temperature and moisture regimes.

Additional keywords: Erwinia spp. ecology, serology, sugar beet, root rot.