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Study of Plasmodiophora brassicae Wor. DeWolfe, Moyra Kathleen

Abstract

Reports concerning the life history of Plasmodiophora brassicae Wor. are highly conflicting. The contradictions in the literature on the subject and the difficulties encountered in the initial phase of the present investigation brought about an inquiry into the techniques employed by previous workers. Repetition of these techniques indicated that many previous experiments had not taken into consideration the problems inherent in an in vitro study of Plasmodiophora brassicae. Conclusions drawn from such experiments are thus of doubtful value. Methods described as successful by earlier investigators were employed in an attempt to stimulate germination. The germination process was not observed, and contaminants introduced with the resting spore material made it impossible to designate any one motile organism as P. brassicae. Attempts were made to obtain root hair infection. Pour methods described by previous investigators proved unsuccessful. A limited degree of infection was obtained by placing young cabbage and cauliflower seedlings in a buffered nutrient solution containing washed P. brassicae resting spores. In spite of the fact that artifacts were readily produced, early infection stages were observed and photographed and the existence of a zoosporangial stage in the root hair was confirmed. The infection rate was too low to permit intensive observations of the development of the parasite within the root hair. A proteolytic enzyme preparation was somewhat successful in increasing the infection rate. This was taken as an indication that a combination of enzymes could provide the necessary germination stimulus. Decay of the host tissues is apparently necessary to the maturation of the resting spores. Present experiments indicated that it is not feasible to separate the contaminants from these spores. As it was not possible to draw conclusions from contaminated cultures, it is concluded that the only approach of value is to provide an artificial germination stimulus to spores from clean clubs, so that the development of the parasite may take place under sterile conditions.

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