7 

 ratio of inoculum density to infection incidence was lowest in fumigated 



soils and highest in fumigated soils with the antagonists added (Fig. 



1-A). 



Slopes of regression lines plotted with data from the growth- 

 chamber experiments of LogjQ (Log l/l-X), where X is the proportion of 

 infected plants, on Logjg inoculum density were 0.82 (r = 0.98), 0.98 

 (r = 0.97), and 0.99 (r = 0.99) with fumigated soil, nonfumigated soil, 

 and fumigated soil plus antagonists, respectively (Fig. 1-B). The 

 inoculum densities required for 50% infection of plants (ID eg) in each 

 soil were interpolated to be approximately 300, 900, and 6500 chlamydo- 

 spores per gram of air-dried soil in fumigated soil, nonfumigated soil, 

 and fumigated soil plus antagonists, respectively. 



When the initial inoculum density of the pathogen was 500 chlamydo- 

 spores per gram of air-dried soil , populations increased after 2 wk to 

 4000 propagules per gram of soil in fumigated soil, remained constant 

 in nonfumigated soil , and decreased to 50 propagules per gram of soil 

 that had been fumigated and amended with antagonists. 



In the greenhouse experiments, the antagonist amendment reduced 

 significantly (P = 0.05) the mean lesion length and the incidence of 

 disease (Table 1 ) . The analysis of varience also showed that the inoc- 

 ulum density of the pathogen and the pathogen inoculum density-antagonist 

 interaction significantly affect disease incidence and mean lesion 

 length (P = O.Ol). There were no significant correlations between 

 treatments and root weight or percent infection. All of the treatments, 

 including the controls, had infection incidences of over 90%. 



