Microhjo] :8 



saprophytes. Weindling (33,3U,35) demonstrated the parasitism of the 

 pathogenic fungus Rhizoctonia solani by the saprophytic fungus 

 Trichoderma viride , the production of the antibiotic gliotoxin, by 

 Trichoderma , and the fact that antibiosis by Tri choderma could be 

 secured only in an acid soil. These several contributors, together 

 with other workers, thus showed that the saprophytic microflora was 

 an imoortant factor in the ecology of the root-invading fungi. In 

 speaking of this earlier work. Garret (36) has suitmed it up admirably 

 in the following paragraph: 



"The marriage between plant pathology and soil microbiology, 

 now comsummated, was followed by a honeymoon period of vm- 

 bounded optimism, during which the most extravagant hopes 

 were entertained for the progeny of the union, to be chris- 

 tened 'Biological Control.' The first optimistic forecasts 



of the prospective god-parents were dimmed by anxiety 



when it was eventually realized that the pregnancy would be 

 unexpectedly long and difficult. One child, indeed, was 

 still-bom, and was q\iietly laid to rest vinder a tombstone 

 inscribed 'Biological Control by Inoculation of the Soil 

 with Antagonistic Microorganisms, ' even though some of the 

 bereaved claim that it was buried alive and is, in fact, 

 still faintly breathing. Other children of the marriage, 

 though at first puny, are still alive and slowly progress- 

 ing, and more promising ones m.11 assuredly be bom in due 

 course." 



It is not necessary for us here to discuss antibioses generally or 

 the principles of antibiotic action. We need only to pause suffi- 

 ciently long to note the extent to which microbial interactions have 

 been found to affect the microflora at the root surface. Some work 

 already has been cited showing that root-invading fungi are less 

 destructive in their attacks on plants in the presence of a vigorous 

 saprophytic microflora. A statement should be interjected here that 

 in the following paragraphs, almost without exception, examples cited 

 will have a strong phytopathological flavor. There are both economic 

 and procedural reasons why most of the work thus far performed has 

 been concerned with the root parasites. 



Selecting one example, among many, of antibiosis at the root surface, 

 we may mention the observation of Eaton and RLgler (37) that the corn 

 plant, never known to be attacked by the cotton root rot fungus in 

 normal culture, succumbs readily when grown in sterile culture com- 

 pletely lacking root surface bacteria. We could turn to the observa- 

 tions of numerous other workers who have concerned themselves with the 

 Streptomyces scabies scab on potatoes, with the Rhizoctonia seedling 

 and root diseases of a number of plants, with the many similar damping- 

 off and root diseases caused by Phytophthora and Pythium species, or 

 with other diseases caused by Ophiobolus , Helminthosporium , or Pu sariuni . 

 For each, there are reports that antibiosis presumably plays an impor- 

 tant role in protecting plants from soil-borne parasites. For those of 



