BIOTIC STRESS RELIEF ON PLANTS IN HYDROPONIC SYSTEMS

Soilless cultivation techniques or hydroponic growing systems are designed to provide plants with best growing conditions in order to achieve optimum yield. But even under these conditions stress may occur on plants grown in soil as well as soilless, although at different extent, in shorter or longer periods, and more severe and pervasive. Stress can be caused by temperature (heat and cold), too much or too little nutrient supply, drought, salinity, pathogens, but also by insufficient or excessive light and oxygen or carbon dioxide. Therefore, the introduction of so-called beneficial microorganisms (BMO) into different growing systems may prevent either prophylactically or moderate stressing situations. The advantage of applying BMO in controlled growing systems such as hydroponics or soilless can improve efficiency and prolonged activity of BMO due to the lack of competition occurring in soil. In this paper the focus will be on the free-living and more loosely attached root bound bacteria of the group of plant growth promoting rhizobacteria (PGPRs). The other well-known symbiosis of plants and rhizobia, the arbuscular mycorrhiza fungi (AMF) will not discussed here, although both groups are important for biotic stress relief.