21 



Results 



The infection incidence of tomatoes by F. oxysporum f . sp. radicis- 

 lycopersici was correlated with the inoculum density of the pathogen in 

 nonamended (r = 0.99) and amended (r = 0.86) soils when the pathogen 

 was added to soil samples taken every 7 days during recolonization of 

 fumigated soils (Table 2, Treatment 1,2). Populations of the pathogen 

 and infection incidence were correlated (r = 0.93 and 0.90, respectively) 

 with the natural logarithm of the total number of fungal propagules 

 detected in the nonamended soils. The inoculum density of the pathogen 

 and infection incidence also were correlated (r = 0.89 and 0.9^, respect- 

 ively) with the natural logarithm of the total number of fungal propa- 

 gules detected in the amended soils. No population of a single genus of 

 antagonists had a correlation greater than r = 0.85 with either the 

 infection incidence or inoculum density of the pathogen. 



The proportion of infected tomato plants was directly related to 

 the ability of the pathogen to proliferate in soils which contained 

 different fungal communities (Fig. 2,3). In the recolonization experi- 

 ments, the highest infection incidence and the highest pathogen popula- 

 tions occurred h days after fumigation (Fig. 2,3). The populations of 

 naturally occurring recolonizers were low or not detected in the soil 

 at that time (Table 3i*0« In both amended and nonamended soils, 

 saprophytic growth of the pathogen and infection incidence decreased 

 with time after fumigation. The incidence of infection eventually 

 stabilized at approximately 1% in amended and nonamended soils. The 

 rapid decrease in both the population of the pathogen and in the 

 incidence of infection in nonamended soils by 18 days after fumigation 



