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Changes in the microbial population of apple leaves associated with the inhibition of the perfect stage of Venturia inequalis after urea treatment
Author(s) -
CROSSE J. E.,
GARRETT CONSTANCE M. E.,
BURCHILL R. T.
Publication year - 1968
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.1744-7348.1968.tb04526.x
Subject(s) - biology , venturia inaequalis , urea , population , ascospore , botany , antagonism , microbiology and biotechnology , fungus , microorganism , bacteria , biochemistry , fungicide , spore , genetics , demography , receptor , sociology
SUMMARY Treatment of detached apple leaves in October with urea induced a rapid and prolonged increase in the microbial populations present in the leaves during the winter. These effects were accompanied by a major shift in the population balance from a predominantly Gram‐positive, chromogenic type of microflora to one dominated by Gram‐negative and non‐chromogenic organisms. Fluorescent pseudomonads became particularly numerous in the urea‐treated leaves and many were found to suppress the development in vitro of Venturia inaequalis. An organism forming yellow colonies, possessing exceptional activity against the scab fungus, which was also found in urea‐treated leaves, was shown to be a Gram‐negative, peritrichous bacterium. No antagonistic organisms were isolated from untreated control leaves, but many were found–usually chromogenic forms–which appeared to stimulate the scab fungus in vitro. Treatment with urea accelerated the decomposition of the leaves and suppressed the development of V. inaequalis in the portions of the laminae which remained structurally intact until the following spring. Many of the effects of urea were enhanced by the addition of glucose, streptomycin, or a suspension of a Pseudomonas sp. isolated from leaves during the winter. Streptomycin alone reduced the total numbers of microorganisms in the leaves but increased the proportion of Gram‐negative organisms: this was associated with diminished ascospore production in the spring. There was no direct evidence that the antagonistic flora stimulated by urea was responsible for the inhibition of V. inaequalis , and alternative explanations are suggested.