PROSPECTS FOR MICROBIAL STABILIZATION IN THE HYDROPONIC CULTURE OF TOMATO USING CIRCULATING NUTRIENT SOLUTION

In Sweden, the cultivation of tomato in closed greenhouse systems is becoming increasingly important. As legislation prohibits the use of chemicals against fungal root diseases in cultures with continuous harvesting, the suppression of pathogens in the nutrient solution and the root zone by microbial stabilization is therefore at present under consideration. By the use of selected microorganisms adapted to the target environment microbial stabilization aims at promotion of plant growth, antagonism of the fungal pathogens and degradation of accumulating organic compounds that may damage the plants and reduce their yield. Preliminary results from our experiments show that growth could be promoted and Pythium spp. could be antagonized by specific bacterial isolates under laboratory conditions. The bacterial isolates tested even promoted growth under greenhouse conditions in respect to leave development and number of flowers in the first truss. Here, the incubation of a mixture of PGPR- (plant growth-promoting rhizo-bacteria)- strains was superior to incubation with single strains. Preliminary results from studies of the degradation of phenolic acids by root- and nutrient solution-inhabiting isolates showed that root-inhabiting bacteria were more tolerant to high concentrations of phenolic compounds than isolates from the nutrient solution. All three topics of microbial stabilization are currently under study in order to find appropriate combinations of bacterial strains for the promotion of plant growth and antagonism as well as for the degradation of organic compounds in closed hydroponic greenhouse systems.