Chapter VII — 115 — Antagonistic Properties 



These organisms were perfectly compatible on potato dextrose agar, as 

 well as in a steam-sterilized soil medium. The control of scab (299), 

 therefore, was said to have been due, not to the direct action of S. frae- 

 cox, but to certain other undetermined microorganisms favored by the 

 presence of the green manure. S. scabies was found (379) to be very 

 sensitive to various products of fungi and bacteria. When grown in 

 close proximity to various bacteria, the acid production of the latter 

 inhibited S. scabies to a considerable degree. Its complete inhibition 

 was not due to the acid reaction alone, however, since a certain bacte- 

 rium which definitely inhibited the growth of this plant pathogen was 

 also isolated from the soil, thus suggesting the possibility that the bac- 

 terium may have exerted the antagonistic effect. 



Goss (146, 147) observed that the severity of scab is dependent on 

 the amount of S. scabies present in the soil. This amount was believed 

 to be controlled by the soil microflora. No evidence was obtained as to 

 whether the effect of the soil flora on S. scabies was due to specific or- 

 ganisms. Kjeszling (217, 218) isolated two cultures of bacteria which 

 were antagonistic to S. scabies. When added to the soil, these bacteria 

 prevented the development of scab on potatoes. 



Among the other antagonistic effects of actinomycetes that may 

 prove to be of great economic importance is their action upon nitrogen- 

 fixing bacteria. Konishi and Fukuchi (229) have shown that cer- 

 tain actinomycetes are able to inhibit the growth, on the plate, of root- 

 nodule bacteria; some of the organisms, like S. flavus, were particularly 

 inhibiting. In association with actinomycetes, none of the nodule cul- 

 tures grew readily. In the soil, however, no effect of the actinomyces 

 cultures was observed upon alfalfa bacteria. 



The inhibiting effect of actinomycetes upon the growth of Azoto- 

 bacter was first observed by Nikolaieva (323) in 1914. Nickell and 

 BuRKHOLDER (322) found in the soil a large number of actinomycetes 

 that exert a marked inhibiting effect upon the growth of Azotobacter. 

 It was suggested that antibiosis may be responsible for development of 

 these organisms in the soil. 



The antagonistic effects of actinomycetes upon plant pathogenic 

 bacteria has also been well established. Hino (173) isolated several 

 actinomvcetes active against Ps. solanacearmn. Corynebacteriuvi se- 

 fedonictun, the causative agent of root rot of potato was antagonized 

 by various actinomycetes, some of which produced antibiotic substances 

 and one produced lysis of the bacterium (335). Further studies on this 

 subject were made by McCormack (275). The ability of actinomy- 

 cetes to produce substances active against bacterial viruses or phages has 

 also been established (198). 



In a natural environment, such as the soil, the development of the 

 antagonistic properties among actinomycetes will occur largely under 

 aerobic conditions. In a less well oxidized environment the actino- 

 mycetes may themselves be antagonized. A bacterium, like B. viega- 



