Accuracy of a Plant-Infection Technique for Counting Populations of Rhizobium trifolii

A "plant-infection" technique for identification and estimation of populations of Rhizobium is described and compared with petri dish colony counts of the same bacterial populations. Provided that bacterial suspensions are agitated thoroughly, dilutions made at 4 C, and test plants grown on agar, the plant-infection technique is an accurate method of estimating R. trifolii in pure culture or when added to soil. The results are discussed in relation to previous investigations of the subject. Tables are presented which, when applied to the distribution of positive (nodulated) test plants in either fivefold or tenfold dilution series, permit calculation of most probable numbers, and confidence limits are stated.