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Resistance

Population Dynamics of Erwinia carotovora pv. carotovora in Potato Stems. M. K. Rahimian, Graduate research assistant, Department of Plant Pathology, University of Wisconsin-Madison, Madison 53706; J. E. Mitchell, professor, Department of Plant Pathology, University of Wisconsin-Madison, Madison 53706. Phytopathology 74:217-220. Accepted for publication 6 September 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-217.

Inoculum (2 × 10³ cfu per plant) of Erwinia carotovora pv. carotovora micropipetted into a potato stem at a leaf axil increased logarithmically in the stem tissue of potato cultivar Norgold Russet, but increased less rapidly in similarly inoculated Russet Burbank potato plants. The population of a weakly virulent strain increased less rapidly than that of a highly virulent strain that caused rapid death of the plants. This weakly virulent strain caused only slight necrosis at the point of inoculation when inoculum of 2 × 10⁷ cfu per plant was used. In infectivity titration tests, specific inoculum doses ranging from 10⁸ to 10² cfu per plant were injected at a leaf axil of each plant by means of a capillary pipette. Probit analysis of quantal responses (number of stems showing soft rot) of potato cultivars to the highly virulent strain gave ED₅₀ values of 1.27 × 10⁵ for the susceptible Norgold Russet and 1.36 × 10⁷ for the more resistant Russet Burbank. A soil strain, serogroup XXIX, was less virulent than a highly virulent strain isolated from a potato stem.