THE BACTERIZATION OF HORTICULTURAL SUBSTRATES AND ITS EFFECTS ON PLANT GROWTH

B. DIGAT
In rhizospheric soil there are many microorganisms and a lot of interactions occurs between them. In contrast, certain horticultural substrates are microorganism-poor. Moreover, artificial substrates such as Perlite or fibrous substrates (Rockwool, Polypropylene and wood fibers) are almost bacteria free. The problem of establishing a beneficial microflora in these substrates is becoming necessary as much for promoting growth as for improving plant protection.

Many recent studies provide useful information showing some Pseudomonads belonging to the Pseudomonas fluorescens-putida group have a positive effect on plant growth and are named "Plant-Growth-Promoting-Rhizobacteria" (PGPR).

In this paper, some selection criteria of PGPR strains such as rhizosphere competence, intensive slime and pigment production, thermo and osmo-tolerance are considered. The conditions of inoculum production are described with emphasis on the problem of inoculum formulation. Specially, a new formulation in granulate was recently performed and gives satisfactory results for substrates bacterization. Methods of substrates inoculation are given and certain causes of check such as the drop of bacterial population are analysed. Particularly to obtain an obvious effect on plant growth, the number of bacteria per root centimeter must not drop below 103 to 104 and is named "biostimulation threshold".

Some experiments with successful results obtained in peat concerning Lettuce, Tomato, Chrysanthemum, Pelargonium and ornamental Malus are described and show growth promotion can be effective on emergency stimulation (Tomato), plantlet root and well-rounding precocity (Lettuce), branching (Malus, Pelargonium, Chrysanthemum) cutting yield (Chrysanthemum, Pelargonium).

The artificial substrates seem particularly well adapted to bacterization specially because their quasi-sterility. Making disease supressive substrates using several types of antagonistic and symbiotic microorganisms could become nextly a reality.

DIGAT, B. (1988). THE BACTERIZATION OF HORTICULTURAL SUBSTRATES AND ITS EFFECTS ON PLANT GROWTH. Acta Hortic. 221, 279-288
DOI: 10.17660/ActaHortic.1988.221.30
https://doi.org/10.17660/ActaHortic.1988.221.30

Acta Horticulturae