A NODULATION-INHIBITING ROOT EXCRETION FROM A NON-NODULATING SOYBEAN STRAIN

A non-nodulating, near-isogenic soybean strain has been shown to release, during growth, a substance that inhibits nodulation of its normally nodulating sister strain. In greenhouse experiments, inoculated seedlings of both strains were transferred to vessels containing aerated, nitrogen-free, Hoagland's nutrient solution. Two plants per vessel were established in the following combinations: one nodulating and one non-nodulating, two nodulating, or two non-nodulating. Root excretions from the mutant resulted in highly significant decreases in nodulation of the normal plants. In addition, presence of the mutant also resulted in decreased total nodule weight, total dry weight, and total nitrogen per nodulating plant. Nodulation in ladino clover, when grown in nutrient solution, was also significantly inhibited by the presence of the mutant soybean. The excretion apparently does not inhibit growth of Rhizobium japonicum.