The multiplication of a specific bacteriophage combined with the host bacterium under a certain environmental condition has a definite passway. Namely, a specific phage-bacterium complex gives always a constant latent period, rise period and average burst size under a certain environmental condition. Based upon these facts, a method was newly deviced to determine the number of the living cells of a certain phytopathogenic bacterium within soil and other materials. The method is as follows: 1) The latent period, the rise period and the burst size of the phage-bacterium combination, in question, have at first to be determined. 2) One-Step growth experiment of the phage is then given with the material containing the bacterium in question under multiple infection. 3) Then the number of the living cells of the bacterium (N) will be obtained by the following formula: N= Total number of phage particles produced
Average burst size 4) When the number of the living bacterium is too small to obtain satisfactory results, the second application of the infection of the phage is required, adding the bacterial suspension into the centrifuged supernatant fluid of the phage of stationary period so that the single-infection of the phage is obtained. 5) In the latter case the calculation of the number of the living cells of the bacterium (N’) is as follows: N’=Total number of phage particles produced
(Average burst size)^2 6) The outline of the whole procedure is given in figure 1. Some examples with the application of this method were shown being used Xanthomonas oryzae No.49 and its phage (Op1 phage). From the results, it was found that X. oryzae could survive in the drought soil for a certain period, and that the multiplication within the leaves of rice plants of resistant variety was inferior to that of the susceptible ones.
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