152 FUNGI AS ANTAGONISTS 



growth not only of the particular fungus but also of other members of 

 the same genus, but not of Fusarium- conglutinans . These bacteria pro- 

 duced a diffusible agent that inhibited the growth of H. sativum 

 (i 15a). The active substance was not destroyed by autoclaving^ it dif- 

 fused into fresh agar and water, producing "stale water" that was in- 

 hibitory to the fungus. 



Chudiakov (143) isolated from the soil two bacteria that were capable 

 of bringing about the lysis of different species of Fusarium as well as 

 other fungi. These bacteria were found to be widely distributed in most 

 soils J they were absent, however, in flax-sick soils, in spite of the abun- 

 dance of Fusarium. When this fungus was added to the soil containing 

 antagonistic bacteria, it did not develop, and the plants did not become 

 diseased. The antagonistic action of a variety of other bacteria against 

 plant pathogenic fungi has been definitely established, as in the case of 

 B. simflex against Rhizoctoniay P. vulgaris against Phyio-phthora 

 (488), and B. mesenlericus against H elminthosforiuin (142). B. sim- 

 plex was grown (491) for 7 days at 28° C. in potato-dextrose medium 

 containing i per cent peptone, and the active substance was removed by 

 charcoal and dissolved in alcohol. Different fungi differed in the de- 

 gree of tolerance to this substance. The majority were repressed when 

 10 per cent concentration of the stale medium was added to fresh 

 medium. 



The ability to produce a thermostable substance toxic to the plant- 

 disease-producing fungus Rhizoctonia is widespread among spore-form- 

 ing bacteria. The toxic substance is insoluble in ether, chloroform, and 

 benzol, but is soluble in ethyl alcohol. It passes through collodion, 

 cellophane, and parchment membranes. It is readily destroyed on boil- 

 ing in alkaline media but is more resistant in acid media. 



Nakhimovskaia (672) found that various bacteria are able to inhibit 

 the germination of rust spores. Nonspore-forming bacteria, such as Ps. 

 ■fluorescens and S. marcescenSj prevented the germination of the spores 

 of Ustilaga avenaey Ustilaga hordeiy Ustilaga nuda^ and Ustilaga reae. 

 Spore-forming bacteria, including B. mycoides and B. 'mesenlericus ^ as 

 well as sarcinae (5. ureae, S. lutea), exerted no antagonistic action on 

 the rust spores. The presence of these bacteria, however, influenced the 

 nature of the germination of the spores, which gave rise to mycelium- 



