The growth of nodule bacteria in the expressed juices from legume roots bearing effective and ineffective nodules

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Abstract
Strains of pea and soy-bean nodule bacteria, differing in their effectiveness in benefiting the host legume, were grown in media containing the unheated root juices from uninoculated host plants and from host plants bearing effective and "ineffective" nodules, and their growth was measured. The growth of the different bacterial strains on root juice from uninoculated plants was not correlated with their effectiveness. The juice from roots with effective nodules produced significantly better growth of the bacteria than juice from roots with ineffective nodules in 27 comparisons out of 44, the differences in the remaining comparisons being insignificant. The juice from roots with effective nodules produced significantly better growth than the juice from uninoculated roots in 10 comparisons out of 25, and significantly poorer growth in 3 comparisons. The juice from roots with ineffective nodules produced significantly poorer growth than the juice from uninoculated plants in 11 comparisons out of 25, and better growth in only 1 comparison. The production, as a result of infection, of soluble substances affecting growth of the bacteria, affords an explanation of those differences in nodule growth that determine the effectiveness or ineffectiveness of the different strains of bacteria as regards N fixation within the host.

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