22 

 occurred as natural populations of Trichoderma spp. increased ^00-fold 



between 11 and 18 days after fumigation (Table 4). 



The rate of immigration of naturally occurring fungal species was 

 slower in soil amended with antagonists than in nonamended soil (Table 

 3,^). Thirty-nine days after fumigation, Gladosporium spp. and a wet 

 spored Mucor sp. were the only naturally occurring species isolated 

 from amended soils, whereas ten different naturally occurring species, 

 including Trichoderma sp. and Penicillium sp. , were isolated from non- 

 amended soils. It was not possible to determine if the dominating popu- 

 lations in amended soils were from the original introduced antagonists, 

 but the species were the same as those introduced. 



The frequency of isolation of any particular species varied with 

 time and treatment (Table 3>*0« Aspergillus ochraceus dominated amended 

 soils during the early stages of recolonization, and it accounted for 

 hd% of the total number of propagules isolated 4 days after fumigation. 

 The majority of the isolates from amended soils 11 and 18 days after 

 fumigation were T. harzianum . Beginning 18 days after fumigation, Q5% 

 of the total number of colonies were either P. restrictum or T. 

 harzianum . In amended soils, the introduced species always accounted 

 for at least 98% of the total number of fungi isolated. 



Some species of fungi were isolated frequently in freshly fumigated 

 soil but occurred less frequently with time. In nonamended soils, 

 Geotrichum sp. , Cephalosporium sp. , and Gylindrocarpon sp. were not 

 isolated past 18 days after fumigation. Pythium sp,, Syncephalastrum 

 sp. , Gunninghamella sp. , and Rhizopus sp. were not isolated from non- 

 amended soils until 39 days after fumigation (Table 4) . 



