CONTROL OF PATHOGENIC FUNGI 311 



The inoculation of sterilized soil with F. graminearum led to the in- 

 evitable death of wheat plants, but additional inoculation of the soil 

 with lysogenic bacteria protected the wheat from the disease. The addi- 

 tion of bacteria to unsterilized soil which has been made sick by con- 

 tinuous growth of flax markedly lowered the percentage of plants dis- 

 eased by F. lint. 



The term "bacterization" was suggested by the Russian investigators 

 (46, 673) to designate the process of treatment of seed with lysogenic 

 bacteria, whereby the plants are protected against pathogenic fungi. 

 The susceptibility of plant seedlings to infection by fungi could be 

 decreased not only by the specific antagonistic bacteria, but also by the 

 presence of other bacteria which are able, in one way or another, to re- 

 tard the development of the fungi. The conclusion was reached that the 

 effect of bacteria on germinating seeds is due to the metabolic products 

 liberated by the bacteria, which are capable of depressing the develop- 

 ment of parasitic fungi. By treating flax seeds with the culture filtrate of 

 the antagonistic bacteria, a similar or even greater decrease in the num- 

 ber of diseased seedlings was obtained. The nature of the active sub- 

 stance produced by the antagonists was not investigated further. It was 

 said to accumulate in 5-to-io-day-old cultures. Heating at 80° C. for 

 10 minutes had no effect upon the substance, but heating at 100° C. 

 brought about its inactivation. 



Jensen (467) concluded that the beneficial result of bacterization is 

 due not to nitrogen-fixation by A-zotobacter or to production of growth- 

 promoting substances by microorganisms, but to the protection of the 

 seedlings against plant pathogens by specific bacterial antagonists. 



Although it has now been definitely established that certain organ- 

 isms can repress or even destroy disease-producing fungi, the utilization 

 of specific microbial products for the control of plant diseases has made 

 comparatively little progress so far. Leemann {SS^) tested the action 

 of various secretions and extracts of microorganisms upon H. sativum. 

 He concluded that microorganisms, pathogenic or nonpathogenic, can 

 supply substances useful as preventive measures against plant patho- 

 gens. No favorable effects upon the development of Rhizoctonia disease 

 in plants could be observed, however, from the application to soil of cer- 

 tain bacterial and fungus products. 



