16 

 In more diverse communities which develop later, the few r-selected 



species are replaced by a number of k-selected species, which grow 



slower and utilize the available resources over a longer period of time. 



The later successional stages have communities of increased diversity 



and stability (22). Although k-selected species coexist with other k- 



selected species, the r-selected species are usually unsuccessful in the 



presence of the more diverse k-selected communities. Control of an r- 



selected pathogen may be possible by establishing other r-selected 



species before the pathogen is introduced or by establishing k-selected 



species before or after the introduction of the pathogen. 



Since the early studies of biological control, biological agents 

 have been selected for their antagonistic properties toward the patho- 

 gen in various laboratory tests outside of the soil environment (2). 

 The results of these tests usually have not been repeatable under field 

 conditions. In the present series of experiments, antagonists were 

 selected for their abilities to proliferate in freshly treated soil, to 

 occupy the root environment of the host, and to increase the ratio of 

 inoculum density to infection incidence, as discussed in Section I. All 

 of these factors were evaluated using field soil, rather than agar, as 

 the growth medium. The selection for antagonists that were successful 

 competitors, rather than for those that produce toxins or show hyper- 

 parasitism on agar plates, may result in the successful control of other 

 plant diseases in which the epidemic is dependent upon the saprophytic 

 growth of an r-selected pathogen. 



The objectives of this study were: 1 ) to determine the effect of 

 fungal communities on the saprophytic development of F. oxysporum f . sp. 



