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ISHS Acta Horticulturae 477: IV International Symposium on Replant Problems

SPECIFIC REPLANT DISEASE REDUCED BY PGPR RHIZOBACTERIA ON APPLE SEEDLINGS

Authors:   B. Biró, K. Magyar, Gy. Várady, M. Kecskés
Abstract:
65 siderophore producing, fluorescent-putida type Pseudomonas strains have been isolated from the rhizosphere and rhizoplane of lupine, crownvetch, potato and apple. After obtaining pure cultures on King B media, plant growth promoting (PGPR) effect and antagonistic (biocontrol) activity were tested in vitro against Erwinia carotovora, Fusarium oxysporum, Sclerotinia sp. The most antagonistic strains were selected for artificial inoculation of apple seedlings. Three types of soils with special replant problems were used in pots under greenhouse conditions. The treatments were roots of apple seedlings soaked in the bacterial suspension of selected, antagonistic PGPR strains before planting, the same procedure was supplemented by adding and mixing the suspension into the soil, and repeated irrigation treatments with the antagonists.

Out of 65 isolates, 20 showed antagonism against the phytopathogenic microorganisms. More than 100% plant growth promotion effect developed as a function of soil types with 12 - 40 strains that were also strongly influenced by the various environmental factors. More fluorescent siderophore were produced by the most antagonistic pseudomonads using a low iron medium. PGPR effects were increased depending on the inoculation frequency using the suspensions of selected antagonistic, fluorescens-putida type pseudomonads. The positive growth stimulation in the inoculated, steamed and also in the unsterilized "sick" soils suggest, that factors such as the persistence and/or hormone productions other than the antibiosis may be involved in the beneficial effects. No correlation was observed between the homologous (apple) and non-homologous (legumes, potato) Pseudomonas isolates and the rate of growth stimulation of the apple seedlings.

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