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Streptomyces scabies and its habitat Baker, Robert Arnold


A study involving variation in strains of the potato scab organism as isolated from a soil in British Columbia is reported. Associated with this is a study of soils from scab-free and scab-infested areas. Exchange capacity and related studies of a number of soil samples indicate a trend toward higher average exchange capacity, higher average exchange calcium and higher average calcium-potassium ratios in the samples from scab-infested areas. There is also a trend toward higher organic matter content and lighter soil textures in the scab-producing soils. In spite of these trends no definite correlations can be established under the method of soil sampling adopted. Thirty-four strains of Streptomyces scabies isolated from diseased White Rose tubers grown on the ranch vary markedly in cultural characteristics and in pathogenicity. The effect of hydrogen ion concentration on four of these strains shows a positive correlation between pH, amount of growth and hydrogen ion concentration up to the optimum pH of 7 to 8 and beyond this range a negative correlation exists. The inhibiting acid pH is 3.4 for two strains and between 4.0 and 5.5 for the other strains. The limiting alkaline pH appears to be beyond pH 11.6. Microphotographs of the Streptomyces scabies show typical open spirals and chains of conidia 0.5 to 1.0 microns in diameter. Scab control measures conducted in pots in the greenhouse and using a severely scab-infested soil sample from the ranch indicate no control by mercuric chloride applications. Applications of sulphuric acid, sulphur and calcium hydroxide indicate that a pH of 8.0 or greater is an effective but not complete control. An acid pH of 5.0 gives less control than pH 8.0 and more acidic reactions give even less control. The applications of these necessary to effect control are too high to be of practical value. The fungicidal effect of compound P-162 as determined under laboratory procedures is no indication of its efficacy in the field or greenhouse. Laboratory technique indicates that most strains are completely inhibited at 100 to 230 parts per million of compound P-162 while in the greenhouse tests 40 parts per million proved effective in giving partial control. The practical value of P-162 in the field is as yet to be determined since its commercial value and its usefulness as a control measure in the field is unknown.

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