QUANTITATIVE DETERMINATION OF VIABILITY OF POTATO RING ROT BACTERIA FOLLOWING STORAGE, HEAT, AND GAS TREATMENTS

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Abstract
A method for determining quantitatively the viability of Corynebacterium sepedonicum was developed for use in eradication studies on bacterial ring rot of potatoes. Drops of bacterial suspension dried on glass or jute fibers impregnated with the organism were used as test materials. The number of viable bacteria in a population was derived from the lag period in its time–growth curve based on turbidity development in a liquid medium. It was demonstrated that ring rot bacteria on dry jute can survive storage at: 0 °C. for 6 months with no loss in viability. Although viability decreases with time at higher temperatures, mortality is not complete after 6 months at 28 °C. The thermal death points of the organism for 10 minute exposures were found to be 55 °C. in liquid medium and 125 °C. in dry air for bacteria on glass and 150 °C. in dry air for bacteria on jute fibers. The minimum gas dosage found to achieve complete kill of ring rot bacteria on dry jute libers in 18 hours was 2% ethylene oxide by volume of air or 20% methyl bromide.

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