4 

 major survival structure (37). For the production of chlamydo spores, 



macroconidia were washed from 2-wk-old cultures grown on potato dextrose 

 agar (Difco, Detroit, MI 48201) at 25 C under continuous fluorescent 

 light (3000 lux). The macroconidia formed intercalary chlamydospores 

 after 4 wk of incubation at 10° macroconidia per milliliter of auto- 

 claved deionized water at 28 G in the dark. 



The potential antagonists were isolated from recolonized soils 1 wk 

 after fumigation. A soil dilution of 1 g of air-dried soil in 1 liter 

 of water was plated on potato dextrose agar which contained 1 ml of 

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

 chlortetracycline hydrochloride (Sigma Chemical Co., St. Louis, MO 63178) 

 per liter of medium (PDA-TC). Conidial suspensions of each isolate were 

 obtained by washing 2-wk-old cultures grown on potato dextrose agar at 

 25 C under 10 hr of fluorescent light (2000 lux) per day. Each suspen- 

 sion then was added to 1 kg of freshly fumigated soil (final water 

 concentration = 10% wt/wt). One-half kilogram of the infested soil then 

 was placed in a plastic container and stored at 25 C for 1 wk after 

 which the population density of each isolate was determined by dilution 

 plating on PDA-TC. The remaining soil that had been infested with an 

 individual isolate was placed in 100-ml polypropylene beakers at 80 g 

 of soil per beaker. Two germinated 'Bonnie Best' tomato seeds were 

 placed in each beaker, and the beakers were moved to growth chambers set 

 at 20 C and 12 hr of light (4000 lux) per day. After 2 wk the roots 

 were washed lightly and plated on PDA-TC. One week later the number of 

 colonies of each potential antagonist growing from the roots was used to 

 evaluate its ability to occupy the root environment. Those isolates 



