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Appl. Environ. Microbiol., Jan 1995, 194-199, Vol 61, No. 1
MA de Brito Alvarez, S Gagne and H Antoun
Four commercial composts were added to soil to study their effect on plant
growth, total rhizosphere microflora, and incidence of plant
growth-promoting rhizobacteria (PGPR) in the rhizosphere of tomato plants.
Three of the compost treatments significantly improved plant growth, while
one compost treatment significantly depressed it. Compost amendments caused
only small variations in the total numbers of bacteria, actinomycetes, and
fungi in the rhizosphere of tomato plants. A total of 709 bacteria were
isolated from the four compost treatments and the soil control to determine
the percentage of PGPR in each treatment. The PGPR tests measured
antagonism to soilborne root pathogens, production of indoleacetic acid,
cyanide, and siderophores, phosphate solubilization, and intrinsic
resistance to antibiotics. Our results show that the addition of some
composts to soil increased the incidence in the tomato rhizosphere of
bacteria exhibiting antagonism towards Fusarium oxysporum f. sp.
radicis-lycopersici, Pyrenochaeta lycopersici, Pythium ultimum, and
Rhizoctonia solani. The antagonistic effects observed were associated with
marked increases in the percentage of siderophore producers. No significant
differences were observed in the percentage of cyanogens, whereas the
percentages of phosphate solubilizers and indoleacetic acid producers were
affected, respectively, by one and two compost treatments. Intrinsic
resistance to antibiotics was only marginally different among the
rhizobacterial populations. Our results suggest that compost may stimulate
the proliferation of antagonists in the rhizosphere and confirm previous
reports indicating that the use of composts in container media has the
potential to protect plants from soilborne root pathogens.
Copyright © 1995, American Society for Microbiology
Effect of Compost on Rhizosphere Microflora of the Tomato and on the Incidence of Plant Growth-Promoting Rhizobacteria
Science de la Vie et de la Sante, Pavillon Charles-Eugene Marchand, Universite Laval, Quebec, Quebec, Canada G1K 7P4, and Premier Research Center, Premier Peat Moss Ltd., Riviere-du-Loup, Quebec, Canada G5R 4C9
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