40 



The population of antagonists consisted of three isolates of 



Trichoderma harzianum Rafai, one isolate of Penicillium restricting 

 Gilman and Abbott, and one isolate of Aspergillus ochraceus Wilhelm. The 

 antagonists were selected for their abilities to increase rapidly in 

 freshly fumigated soil, to occupy the root environment of the host, and 

 to increase the ratio of inoculum density to infection incidence under 

 growth-chamber conditions (Section I). The antagonists were applied at 

 a concentration of 5 X lO- 5 conidia per isolate per plant. One day 

 before use, conidia of each antagonist were harvested from petri plates 

 containing l4-day-old cultures grown on potato dextrose agar at 25 G 

 under 2000 lux of fluorescent light. The antagonists were added to the 

 soil by pouring 25 ml of a conidial suspension over the roots of each 

 transplant after it was positioned in the transplant hole and then 

 adding another 25 ml over the crown of the transplant immediately after 

 the roots were covered with soil. The treatments included infestation 

 of soil with pathogen populations of 0, 50, 500, or 5000 chlamydo spores 

 per plant with or without the addition of antagonists. 



Soil-dilution plating techniques were used to monitor populations 

 of the pathogen and antagonists during the growing season. Soil samples 

 were obtained by preparing composite samples of 5-g subsamples from the 

 crown areas of five plants from each plot. Komada's (l6) medium, which 

 is selective for F. oxysporum , was used to isolate the pathogen from 

 soil dilutions of 1:25, 1:100, or 1:1000 (wt:vol). The pathogen was 

 identified further by a technique developed by Sanchez et al. (29) and 

 discussed in Section I. Potato dextrose agar, which contained 1 ml of 

 Tergitol NPX (Sigma Chemical Co., St. Louis, MO 63178) and 50 mg of 



