摘要:

Studies on the relation of cropping to numbers of bacteria in soil were carried on in an experiment designed for statistical control. Plots were cropped as follows: fallow, three; wheat, three; barley, two; sugar beets, two; soybeans, two; and corn, two. The estimate on each plot is based on counts from 24 plates. A series of from 17 to 20 such estimates, made at weekly intervals from each plot, is available for the analysis. Moisture data are available also. The effect of cropping on numbers of bacteria is shown for each plot as the multiple regression of bacteria on days and moisture reduced to two dimensions by the elimination of moisture.Bacteria respond to a growing crop. This response is similar in replicate plots of one treatment; but is markedly different with different crops.

ISSN:1923-4287    

DOI:10.1139/cjr42c-038

出版商:NRC Research Press    

年代:1942

数据来源: NRC

摘要:

Data on the errors of the plate count method are presented. They are based on changes in numbers of bacteria during the crop season in plots supporting different crops. Duplicate samples were used at each step in the procedure. This provides information on variations associated with sampling, which contribute to the error of the plot estimate on any date.A large portion of the differences among estimates from each plot made on different dates is explained by correlations among numbers of bacteria and changes in environmental factors. Obviously, a large error masks a small relationship.This may be minimized by (1) careful sampling and the use of duplicates at each step in the procedure and (2) collecting data for correlating bacteria with changes in many environmental factors other than the one of chief interest m the investigation.

ISSN:1923-4287    

DOI:10.1139/cjr42c-039

出版商:NRC Research Press    

年代:1942

数据来源: NRC

摘要:

The form of apple tree crown rot that occurs in the irrigated orchards of British Columbia is confined to the below-ground bark tissues of the tree. It has been encountered in trees of all ages and of all the commercial varieties.Proof is given that this crown rot is caused by the fungusPhytophthora cactorum(L.&C.) Schroet. Typical symptoms of the disease have been reproduced in over 200 trees of various ages as a result of their inoculation with this fungus. Isolation has been possible only from the margins of active lesions, and has proved difficult even from these tissues. There is evidence that the activity ofP.cactorumis inhibited in rotted tissues by the antagonistic effect of one or more secondary organisms.The influence of soil moisture and temperature on disease incidence has been studied by field observations and by the inoculation of two-year—old trees under controlled conditions in Wisconsin tank equipment in the greenhouse. The effects of these two factors seem to be interrelated, with the highest incidence of disease in an almost saturated soil at the highest temperature imposed, 32 °C. The influence of soil moisture is exerted particularly in the subsoil, rather than in the locus of crown rot attack.Certain varieties of apple have been found to vary in their resistance to crown rot. Deep wounds have proved necessary to allow entry of the fungus into bark tissues.The additional information now available is being utilized in a search for improved means of combating the disease.

ISSN:1923-4287    

DOI:10.1139/cjr42c-040

出版商:NRC Research Press    

年代:1942

数据来源: NRC