Disease suppressive soilless culture systems; characterisation of its microflora

The trend in glasshouse horticulture has always been to start culture systems as aseptic as possible. However, several root diseases still cause problems under these conditions. The present paper shows the importance of the microflora to suppress Pythium aphanidermatum, a fungal root pathogen which is a serious threat in cucumber. Introduced single antagonists as well as the indigenous microflora suppressed pythium root and crown rot. Pseudomonas fluorescens, Streptomyces griseoviridis, Pythium oligandrum, and 2 isolates of Trichoderma harzianum reduced the disease occurrence by 60 ␘r more in several, but not all, of the experiments. The indigenous microflora showed a very constant disease suppression of 50 to 100 &Eth;This was tested in experiments where P. aphanidermatum was added to sterilised and non-sterilised rockwool, and to sterilised rockwool that had been recolonised with the original microflora. Suppressiveness correlated with the number of filamentous actinomycetes present in the nutrient solution in the rockwool slabs. If a beneficial microflora is present in the cropping system, it should not be disturbed or eradicated by treatments such as disinfection of the recirculated nutrient solution. Therefore, the effects of different disinfection procedures on the composition of the microflora were compared. Numbers of filamentous actinomycetes in the nutrient solution in the tank after the disinfection treatment were highest without disinfection, intermediate after slow filtration, and lowest after UV treatment. Numbers of actinomycetes in the slabs, i.e. around the roots, were not distinctly different between the treatments. The implication of potential shifts in the microbial populations due to certain treatments for the disease development is not known. Increased knowledge on the beneficial microflora and the treatments that influence the composition of such a microflora, will stimulate the exploitation of microbially balanced and optimised soilless culture systems

Disease suppressive soilless culture systems; characterisation of its microflora

The trend in glasshouse horticulture has always been to start culture systems as aseptic as possible. However, several root diseases still cause problems under these conditions. The present paper shows the importance of the microflora to suppress Pythium aphanidermatum, a fungal root pathogen which is a serious threat in cucumber. Introduced single antagonists as well as the indigenous microflora suppressed pythium root and crown rot. Pseudomonas fluorescens, Streptomyces griseoviridis, Pythium oligandrum, and 2 isolates of Trichoderma harzianum reduced the disease occurrence by 60 ␘r more in several, but not all, of the experiments. The indigenous microflora showed a very constant disease suppression of 50 to 100 &Eth;This was tested in experiments where P. aphanidermatum was added to sterilised and non-sterilised rockwool, and to sterilised rockwool that had been recolonised with the original microflora. Suppressiveness correlated with the number of filamentous actinomycetes present in the nutrient solution in the rockwool slabs. If a beneficial microflora is present in the cropping system, it should not be disturbed or eradicated by treatments such as disinfection of the recirculated nutrient solution. Therefore, the effects of different disinfection procedures on the composition of the microflora were compared. Numbers of filamentous actinomycetes in the nutrient solution in the tank after the disinfection treatment were highest without disinfection, intermediate after slow filtration, and lowest after UV treatment. Numbers of actinomycetes in the slabs, i.e. around the roots, were not distinctly different between the treatments. The implication of potential shifts in the microbial populations due to certain treatments for the disease development is not known. Increased knowledge on the beneficial microflora and the treatments that influence the composition of such a microflora, will stimulate the exploitation of microbially balanced and optimised soilless culture systems