. The actinomycetes. Actinomycetales. 268 THE ACTINOMYCETES, Vol. I. 12 10 Figure 104. Influence of pH on the growtli of the potato scab organism (Reproduced from: Dip- penaar, B. J. Union of South Africa Dept. Agr. Sci. Bull. 136: 68, 1933). vary with the soil moisture or the soil re- action. Increasing soil moisture decreased the amount of scab at all soil temperatures and in all types of soil used, and increased the yield of potatoes. Lower moisture was required to control scab at 13 and at 25°C than at either 17 or 21 °C. The disease on actively growing tubers was controlled by increas
. The actinomycetes. Actinomycetales. 268 THE ACTINOMYCETES, Vol. I. 12 10 Figure 104. Influence of pH on the growtli of the potato scab organism (Reproduced from: Dip- penaar, B. J. Union of South Africa Dept. Agr. Sci. Bull. 136: 68, 1933). vary with the soil moisture or the soil re- action. Increasing soil moisture decreased the amount of scab at all soil temperatures and in all types of soil used, and increased the yield of potatoes. Lower moisture was required to control scab at 13 and at 25°C than at either 17 or 21 °C. The disease on actively growing tubers was controlled by increasing the soil moisture after the tubers had developed scab. Relatively scab-free tubers growing in a scab-infested soil with a high soil moisture content will become scabby if the soils are allowed to become dry. In greenhouse experiments, Dippenaar found that a reaction of pli and lower either controlled or reduced the disease in severely scab-infested soils bul did not elimi- nate scab entirely. A reaction of pH and lower, however, had an adverse effect on the potato plant. Goss (1937) made a detailed study of the environmental factors influencing the cau- sation of potato scab by S. scabies. The soil was found to be the major source of infec- tion. Although crop rotation reduced con- siderably the incidence of the disease, the fact that tubers in soil never before planted to potatoes could still show severe scab sug- gested that various other factors were in- volved which influenced the severity of the disease. Among these factors, high temperature, low moisture, alkalinity, abundant aeration, and the addition of barnyard manure are generally accepted as fa\'oring the incidence of the disease. On reading the extensive lit- eratiu'e, one would assume that it should be possible to correlate the occurrence of the disease in the field with one or more of these factors, rnfortimatel}^ it has often been. Please note that these images are extracted from scanned page images
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