Effect of soil physical properties on biological control of damping off in sugar beet
The research is focused on soil factors which can affect Pythium ultimum and the bio control properties of Pseudomonas fluorescens and Bacillus subtilis. Similar studies have previously been carried out with results that were not always consistent. One possible explanation was the occurrence of water flow which can influence the location of antagonist bacteria in the rhizosphere, and thus their competitive action. The innovative point of the work was to design a watering method which minimised the possibility of unwanted water flow. Three soil factors were considered: pH (from 5 to 8), temperature (several regimes between 3 and 25°C) and matric potentials (-10, -100, -300 kPa). Their effect on microbial survival and activity was studied by measuring root colonisation, activity and biocontrol of the antagonistic bacteria. Bacillus subtilis did not show antagonistic activity against Pythium ultimum and its colonisation was not affected by any soil factors investigated. No soil pH effect was found on the biocontrol activity of Pseudomonas fluorescens. The root colonisation of P. fluorescens decreased with increasing temperature and at extreme low matric potential (<-300 kPa). However, between -120 and -140 kPa this bacterium reached its highest level of root colonisation and its greatest antagonistic activity. Under such conditions colonisation data showed that there was downward movement of P. fluorescens which could be explained most likely by nematodes as possible vectors. These results were further investigated during a field test in which using minor doses of antagonistic bacteria no effect of biocontrol treatment against damping off was measured. A distinct study was carried out on forecasting the time to crop emergence from a model of sugar beet emergence with a measured and/or simulated set of data.