FACTORS AFFECTING THE PATHOGENICITY OF BACTERIA TO POTATO TUBERS. I

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Abstract
An isolate of Erwinia aroideae caused much more rotting of potato tubers than did isolates of Pseudomonas sp., Flavobacterium sp., and Pseudomonas syringae; filtrates from cultures of each of the bacteria in potato extract had about the same macerating activity. Pseudomonas sp. and P. syringae, but not Erwinia aroideae or Flavobacterium sp., were agglutinated in three different types of potato extract at the normal pH of potato tubers.Measurements of growth by turbidity and total count methods were compared. In undisturbed potato sap, Erwinia aroideae had grown much more after 12 hr. than had Flavobacterim sp. and Pseudomonas syringae. Erwinia aroideae also grew more rapidly than Pseudomonas sp., but in this case the difference was caused largely by a longer lag phase.The two species of Pseudomonas grew far less rapidly in potato sap cultures shaken hourly than in undisturbed cultures. Erwinia aroideae grew slightly more rapidly in disturbed culture. Measured by the total count method, growth of Flavobacterium sp. was better in undisturbed cultures, but the opposite result was obtained when growth was measured turbidimetrically.With a small inoculum, growth of Erwinia aroideae and of Pseudomonas sp. was delayed by as much as 3 days in potato sap sterilized by heat. This effect was not obtained with an inoculum twenty times bigger, with potato extract, or with sap sterilized by filtration.Potato sap reduced the macerating activity of preparations from each bacterium; oxidation of the sap had no further effect. Production of macerating enzymes by Flavobacterium sp. and Pseudomonas syringae, but not by Erwinia aroideae and Pseudomonas sp., was less in potato sap than in potato extract. Erwinia aroideae secreted macerating enzymes into potato sap much more rapidly during the first 12 hr. of growth than did Pseudomonas sp.The activities of filtrates from cultures of Erwinia aroideae and Pseudomonas sp. were higher at the pH of the culture at the time of sampling than at higher and lower values.The addition of CaCO3 to media apparently increased the pH optimum for macerating activity of Erwinia aroideae and, to a lesser extent, Pseudomonas sp. preparations.There was little difference in the toxicity of preparations of similar macerating activity from cultures of the four organisms.