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BACTERIAL CANKER OF STONE‐FRUITS: IV. INVESTIGATION OF A METHOD FOR MEASURING THE INOCULUM POTENTIAL OF CHERRY TREES
Author(s) -
CROSSE J. E.
Publication year - 1959
Publication title -
annals of applied biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.677
H-Index - 80
eISSN - 1744-7348
pISSN - 0003-4746
DOI - 10.1111/j.1744-7348.1959.tb02546.x
Subject(s) - biology , canker , horticulture , bacteria , botany , pathogen , microbiology and biotechnology , genetics
Pseudomonas mors‐prunorum Wormald, the organism causing bacterial canker of stone‐fruits, was present on healthy cherry leaves during the autumn in numbers sufficient to suggest that they were the main source of inoculum for the infection of stems and branches. Quantitative estimates of the pathogen could be obtained by shaking leaves in water and plating out the washings. This method was examined in detail as a possible means of comparing the inoculum potentials on different cherry varieties. The numbers of the pathogen varied considerably between leaves and between branches, but not between trees of the same variety. It was estimated that a sample of 192 leaves, eight from each of twenty‐four different branches would be adequate to show differences between varieties if sufficiently replicated in time. The accuracy of a twenty‐four branch sample was tested by comparing parallel samples from two separate groups of trees of the same variety. There was a highly significant correlation between the numbers of bacteria obtained from the two series of samples. From the error variance in an analysis of variance, it was calculated that five successive samples would show a significant difference between two such groups of trees if one exceeded the other by 54%. It was necessary to wash leaves for 4 hr. or more, depending on temperature, to recover all the bacteria from the leaf surfaces. At temperatures lower than 27° C. however, bacterial growth intervened before this stage was reached. At laboratory temperatures a period of 4 hr. washing was found to be most suitable for comparing varieties and gave 80–90% recovery of bacteria without errors due to growth. A characteristic flora of non‐parasitic bacteria was observed on cherry trees, coexisting with the pathogen on the leaf surfaces. The fungus Pullaria pullulans was also extremely abundant.