3 



applicable to a system which demands freshly treated soil "because popu- 

 lations of many microorganisms can become established during the time 

 required for the aging of soil infested with the pathogen. An alterna- 

 tive to this method is to infest soil with chlamydo spores produced under 

 axenic conditions and quantified by direct count; a subsequent estima- 

 tion of the population can be obtained by soil dilution plating. 



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

 ships of densities of chlamydospores of F. oxysporum f . sp. radicis- 

 lycopersici to the incidence of infection in fumigated and nonfumigated 

 soils, 2) to determine the effects that selected antagonists have on 

 the relationship of inoculum density to the incidence of infection, and 

 3) to determine the effects of antagonists on disease severity. The 

 techniques and procedures were developed so that they can be applied to 

 any disease which is severe after fumigation due to decreased competitor 

 populations and subsequently increased pathogen populations. 



Materials and Methods 



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

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

 Cultures 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 A) at the rate of 1 kg of fumigant to 50 kg of soil for 2 days 

 in a sealed container and then allowed to air in the greenhouse for *+■ 

 days. 



Chlamydospores of the pathogen were used as inoculum to simulate 

 natural conditions in which chlamydospores of Fusarium spp. are the 



