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Preservation of Corynebacterium insidiosum in a Sterile Soil Mix Without Loss of Virulence. R. B. Carroll, Graduate Assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; F. L. Lukezic, Associate Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 61:688-690. Accepted for publication 21 January 1971. DOI: 10.1094/Phyto-61-688.

Forty-five single-cell isolates of Corynebacterium insidiosum were maintained for 1 year at 4 and 21 C in sterile, distilled water, on beef-lactose agar (BLA), in a sterile 3:1:1 soil:peat:perlite mix. Forty-two of the isolates kept at each temperature in soil persisted over this interval and produced typical colonies when cultured on BLA. No variant colonies were detected. Parent isolates of the single-cell isolates persisted for 20 months in a sterile soil mix with no apparent change. In contrast, all isolates maintained on BLA persisted but grew poorly, produced little of the typical blue pigment, and produced variant colonies. Only 50% of the isolates could be recovered from sterile water. These grew poorly on BLA and produced only a small amount of the pigment. Thirty-two of the isolates held at 21 C on BLA and in sterile soil were tested for virulence. Results showed a loss of virulence for all isolates maintained on agar in contrast to those in soil. No change in virulence due to soil-storage temperature was detected when eight virulent isolates were tested on seedlings grown under sterile conditions. This method is more convenient and reliable than previously described methods, and should be useful for maintaining a large number of isolates for long periods without loss of virulence.

Additional keywords: bacterial wilt, alfalfa.