SECTION II 

 EFFECT OF FUNGAL COMMUNITIES ON THE PATHOGENIC AND SAPROPHYTIC 

 ACTIVITIES OF FUSARIUM OXYSPORUM F. SP. RADICIS-LYCOFERSICI 



Introduction 



The causual agent of Fusarium crown rot of tomato ( Lycopersicon 

 esculentum Mill.), Fusarium oxysporum Schlecht f. sp. radicis-lycopersici 

 Jarvis and Shoemaker, is able to compete as a saprophyte in freshly 

 treated soils. Fusarium crown rot is associated with the rapid sapro- 

 phytic proliferation of the pathogen. Naturally and artificially 

 introduced soil recolonizers may reduce the severity of the epidemic by 

 impeding saprophytic proliferation (l3»2?). 



The competitive saprophytic ability of a pathogen is affected by 

 the community of microorganisms which surrounds it. A soilborne plant 

 pathogen that grows poorly or not at all in nontreated soil may grow 

 readily as a saprophyte in soils in which the microbial community has 

 been disturbed recently, as by the application of a broad spectrum 

 biocide. The successional theory of community ecology states that a 

 series of communities, or sere, develop after such a perturbation (22). 

 Specific serai communities have certain characteristics in common, 

 regardless of whether they are plant, animal, or fungal communities. 

 The early successional communities are of low diversity and are domi- 

 nated by a few species, r-selected species, which grow rapidly and 

 quickly deplete the available resources. The success of a particular r- 



selected species is dependent upon the absence of competitors (22). 



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