17 

 radicis-lycopersici in soil , 2) to monitor the rate of fungal species 



immigration into soils amended or not amended with the antagonists, and 



3) to quantify the effects of fumigation and antagonists on the activity 



of the pathogen in soil and on the host-pathogen interaction. 



Materials and Methods 



The ability of F. oxysporum f . sp. radicis-lycopersici to compete 

 as a saprophyte was quantified by monitoring the pathogen populations in 

 soils in the absence of the host. The pathogenic ability of the pathogen 

 in different soil communities was quantified as the percentage of host 

 plants infected after exposure to pathogen infested soil for 2 wk. 



An isolate of F. oxysporum f . sp. radicis-lycopersici was obtained 

 from a diseased tomato plant collected in a south Florida field. Cul- 

 tures were stored in soil tubes according to the method of Toussoun and 

 Nelson (37). 



Pompano fine sand was treated with methyl bromide-chloropicrin 

 (67/33% v/v) at the rate of 1 kg of fumigant to 50 kg of soil for 2 days 

 in a sealed container. The soil was aired in the greenhouse for k days 

 before further use. 



Ghlamydospores of the pathogen were formed from macroconidia under 

 axenic conditions and quantified by direct count with a standard hemo- 

 cytometer. The establishment of defined initial inoculum densities of 

 the pathogen in freshly fumigated soil was accomplished by methods 

 reported in Section I. 



The antagonists used in the artificial infestation and recoloniza- 

 tion experiments included three isolates of Trichoderma harzianum Rafai, 

 one isolate of Penicillium restrictum Gilman and Abbott, and one isolate 



