3^ 

 The total number of fungal populations detected increased rapidly 



after fumigation and then decreased with time. Kreutzer (l?) attributed 

 the rapid increase in populations of recolonizing fungi to the avail- 

 ability of nutrients. Wilson (43) hypothesized that the rapid increase 

 in organisms following fumigation or other severe perturbation was the 

 result of the growth of noninteractive populations, and that the 

 eventual decrease in populations was the result of interactive popula- 

 tion growth. In the noninteractive stages of recolonization, competi- 

 tion is low because of the large niche space available. In the inter- 

 active stages, however, the populations interact with each other and the 

 effect is an overall reduction in the total number of individuals. 

 Further evidence for the application of the noninteractive model to soil 

 recolonization was obtained when the pathogen was allowed to grow as a 

 saprophyte in the absence of other soil recolonizers. The highest num- 

 ber of total fungal propagules in any of the experiments (10° propagules 

 of the pathogen itself per gram of soil) was obtained when the pathogen 

 was maintained in a noninteractive environment by the exclusion of other 

 competing species. The noninteractive model may explain why the highest 

 inoculum density of total fungal propagules was not associated with the 

 lowest inoculum density of the pathogen or with the lowest infection 

 incidence of the host. Conversely, inoculum density of the pathogen and 

 the infection incidence of the host were closely related to the total 

 populations in amended soils; this was expected because the artificially 

 introduced isolates were selected specifically for their antagonistic 

 actions toward the pathogen, as described in Section I. 



In fumigated soils to which the pathogen was added every 7 days, 

 there were higher correlations of infection or inoculum density with 



