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Applied and Environmental Microbiology, March 2001, p. 1147-1153, Vol. 67, No. 3
Department of Microbial Ecology and
Biotechnology, National Environmental Research Institute,
Roskilde,1 and Department of
Geochemistry, Geological Survey of Denmark and Greenland,
Copenhagen,2 Denmark
Received 3 July 2000/Accepted 21 December 2000
In recent years, the interest in the use of bacteria for biological
control of plant-pathogenic fungi has increased. We studied the
possible side effects of coating barley seeds with the antagonistic strain Pseudomonas fluorescens DR54 or a commercial
fungicide, imazalil. This was done by monitoring the number of
indigenous Pseudomonas organisms and actinomycetes on
barley roots during growth in soil, harvest after 50 days,
and subsequent decomposition. Bacteria were enumerated by
traditional plate spreading on Gould's S1 agar
(Pseudomonas) and as filamentous colonies on Winogradsky agar (actinomycetes) and by two quantitative competitive PCR assays. For this we developed an assay targeting Streptomyces and
closely related genera. DR54 constituted more than 75% of the
Pseudomonas population at the root base during the first 21 days but decreased to less than 10% at day 50. DR54 was not successful
in colonizing root tips. Initially, DR54 affected the number
of indigenous Pseudomonas organisms negatively,
whereas imazalil affected Pseudomonas numbers positively,
but the effects were transient. Although plate counts were considerably
lower than the number of DNA copies, the two methods correlated well
for Pseudomonas during plant growth, but after plant
harvest Pseudomonas-specific DNA copy numbers decreased while plate counts were in the same magnitude as before. Hence, Pseudomonas was 10-fold more culturable in a decomposition
environment than in the rhizosphere. The abundance of
actinomycetes was unaffected by DR54 or imazalil amendments, and CFU
and quantitative PCR results correlated throughout the experiment. The
abundance of actinomycetes increased gradually, mostly in numbers of
DNA copies, confirming their role in colonizing old roots.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.3.1147-1153.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Succession of Indigenous Pseudomonas spp. and
Actinomycetes on Barley Roots Affected by the Antagonistic Strain
Pseudomonas fluorescens DR54 and the Fungicide
Imazalil
*
Corresponding author. Mailing address: Geological
Survey of Denmark and Greenland, Department of Geochemistry, Thoravej
8, DK-2400 Copenhagen NV, Denmark. Phone: 45 38 14 20 00. Fax: 45 38 14 20 50. E-mail: kj{at}geus.dk.
Applied and Environmental Microbiology, March 2001, p. 1147-1153, Vol. 67, No. 3
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.3.1147-1153.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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