INTERACTION BETWEEN RHIZOBIA AND POTATO TISSUES

Several cultivars of Solanum tuberosum L., the potato, were grown on tissue culture media and their roots inoculated with strains of rhizobia known to infect legumes at root junctions or between epidermal cells. Infection incidence and severity showed considerable cultivar/bacterial strain interaction. Bacteria spread through intercellular spaces and invaded cells in a non-structured way: some infections penetrated to the root xylem. There was no evidence that potato root cells produced nod-inducing factors and nitrogenase activity was not detected. In some host/rhizobial combinations outgrowths were formed on roots. These varied from loose infected callus tissue at the junctions of lateral roots, to modified lateral roots of limited growth which showed some colonization by rhizobia.