5 

 which increased populations rapidly in the freshly fumigated soil and 



occupied the root environment then were tested for their potential to 

 increase the ratio of inoculum density to infection incidence in pre- 

 liminary growth-chamber experiments. Of the 26 isolates which fulfilled 

 the first two requirements, the five that were selected for the rest of 

 the tests included three isolates of Trichoderma harzianum Rafai, one 

 isolate of Fenicillium restrictum Gilman aid Abbott, and one isolate of 

 Aspergillus ochraceus Wilhelm. 



Concentrations of conidia of the antagonists and chlamydo spores of 

 F. oxysporum f. sp. radicis-lycopersici were determined by counting 40 

 fields of a standard hemocytometer, and the desired dilutions were added 

 to soil. 



The relationships of inoculum density to infection incidence were 

 determined by experiments done in growth chambers. Two germinated 

 'Bonnie Best' tomato seeds were placed in a 100-ml polypropylene beaker 

 which contained 60 g of infested soil layered over 50 g of autoclaved 

 sand. A range of inoculum densities of the pathogen was used and a 

 composite of the antagonists was added at the constant concentration of 

 5000 conidia per isolate per gram of air-dried soil. Twenty-four 

 beakers of each inoculum combination then were placed in growth 

 chambers. After 2 wk the soil was washed from the roots; the plants 

 were soaked in 0.6% sodium hypochlorite for 1 min and rinsed in auto- 

 claved deionized water. The roots and lower stem were plated on 

 Komada's (l6) selective medium for F. oxysporum and observed after 10 

 days for colonies of the fungus. Populations of the pathogen in the 

 soil from the beakers also were determined after 2 wk of incubation in 

 the growth chamber. The populations of the pathogen were quantified by 



