128 ACTINOMYCETES AS ANTAGONISTS 



ANTAGONISTIC EFFECTS OF ACTINOMYCETES 



AGAINST AGENTS PRODUCING 



PLANT DISEASES 



Various species of Streftomyces are also strongly antagonistic against 

 bacteria causing plant diseases, such as Bacterium solanacearum (426). 

 According to McCormack (593), aerobic conditions are necessary for 

 the development of the antagonistic properties of actinomycetes ; those 

 requiring less oxidized conditions are themselves antagonized. B. mega- 

 theriumy for example, was said to be antagonistic to certain species but 

 was antagonized by others. Vs. -jtuorescens^ however, was antagonistic 

 to actinomycetes as a whole, causing their lysis. 



Actinomycetes possess antagonistic properties not only against bac- 

 teria but also against some other actinomycetes. The more aerobic spe- 

 cies are antagonistic to the less aerobic types. Millard (644) believed 

 that he succeeded in controlling potato scab caused by Streftomyces 

 scabies by the use of green manures such as grass cuttings. The develop- 

 ment of scab on potatoes grown in sterilized soil and inoculated with 

 S. scabies was reduced by the simultaneous inoculation of the soil with 

 Streftomyces fraecoXy an obligate saprophyte. By increasing the pro- 

 portion of the latter organism to the pathogen, the degree of scabbing 

 on the test potatoes was reduced from 100 per cent to nil. The sterilized 

 soil provided sufficient nutrients for the development of the antagonist 

 and only a small increase in the control was obtained when grass cut- 

 tings were added and sterilized along with the soil. 



Sanford (820) was unable, however, to control potato scab by the 

 inoculation, with S. scabies and S. fraecox, of both steam-sterilized and 

 natural soil containing different amounts of green plant materials. 

 These organisms were perfectly compatible on potato dextrose agar, as 

 well as in a steam-sterilized soil medium. The control of scab, there- 

 fore, was said to have been due not to the direct action of S. fraecox 

 but to certain other undetermined microorganisms favored by the pres- 

 ence of the green manure. S. scabies is very sensitive to various products 

 of fungi and bacteria. When grown in close proximity to various bac- 

 teria, the acid production of the latter inhibited S. scabies to a consider- 

 able degree. Its complete inhibition was not due to the acid reaction 



