M) iTobiol 1 7 



f\ini;;al flora were established that wore very siniilir to tho.-.n foiiru) 

 in the natural rhizospheres. 



Tumor (25), working with the fungus Ophiobolus that causes the 

 take-all disease of wheat but that ordinarily does not attack oat 

 plants, fo\ind that the resistance of oat roots was due to an uni- 

 dentified antibiotic substance. The material, even when diluted to 

 one part in a hundred thousand, was effective in reducing the growth 

 of Ophiobolus in laboratory culture. Kirkham (26) found that apple 

 and pear leaves contained phenolic compounds that strongly inhibit 

 the fungi causing black spot diseases of apple and pear. That plants 

 also may produce compounds that are inhibitory to the microfauna, was 

 shown by Ellenby (27). Roots of cruciferous plants that were resist- 

 ant to the potato root nematode were found to contain a mustard oil, 

 allyl isothicocyanate, that prevented the eggs of the parasite from 

 hatching and that was lethal to its larvae. 



Especially interesting is the recent work of Virtanen and Hietala 

 (28,29). In the course of investigating differences in rye seedlings 

 to susceptibility to the snow-mold fungus, Fusarium nivale, these 

 workers isolated a substance strongly inhibitory to the fungus. The 

 substance was separated by cellulose column chromatography, crystal- 

 lized in pure form, and identified as 2(3)-benzoxazolinone, It 

 could not be detected in ungerminated rye seeds, but after 5 to 6 

 days of germination in light at room temperature, the anti-Fusarium 

 factor waf strong. The fact that appearance of the compound in the 

 seedling roots could be correlated to conditions of seedling develop- 

 ment makes the discovery appear an important step forward in explain- 

 ing the environmental effects on seedling susceptibility to root 

 diseases. In the words of Virtanen and Hietala/ the discovery "opens 

 new prospects about the resistance of plants to fungal diseases." 



It would now appear that we can confidently look forward to much 

 further information concerning compoiinds secreted by the roots of 

 different plants or of the same plant at different times and under 

 different conditions. Not only will such information be of great 

 value in plant breeding programs and in achieving effective control 

 of soilborne parasites, but it v/ill also enable us to achieve a much 

 better understanding of the saprophytic microfloras of plant roots. 



How Important Is Antibio sis in Determining the Microflora 

 of the FOiizosphere ? 



The importance of microbial inter-actions or antagonisms in restraining 

 the fiingal parasites of plant roots was recognized by soil and plant 

 scientists many years before the antibiotic wonder drugs became as well 

 known as aspirin, even though, as most of us are painfully aware, by 

 no means as inexpensive. The pioneer vjork of Sanford (30), Millaixl and 

 Taylor (31), and Sanford and Broadfoot (32) showed that scab on potatoes 

 and root rot of wheat could be measurably reduced or controlled, under 

 appropriate conditions, by the antagonistic action of various soil 



