Influence of the Numbers of Rhizobium supplied on the Subsequent Nodulation of the Legume Host Plant

Abstract

The effect of numbers of Rhizobium supplied on the subsequent numbers of nodules formed was tested with Phaseolus radiatus var. aurea in water culture. Nine weeks after inoculation plants supplied with from 88,700 to 887,000 bacteria per c.c. of culture solution bore significantly more nodules than those given from 89 to 887 per c.c. An inoculum of 44,350 per c.c. produced intermediate numbers of nodules. One week after inoculation, the percentage of curled and of infected root-hairs on the seedlings was roughly proportional to the logarithm of the bacterial numbers supplied, while the numbers of nodules produced at this stage already showed a significant difference between extreme doses of inoculum. Nine weeks after inoculation the final nodule numbers were related to the percentages of curled and of infected root-hairs after one week. The final nodule numbers are related to the growth of the root system since the final number of nodules per gramme of root is independent of the initial dose of inoculum, the effect of which was mainly to cause an increase in root growth.