GENERAL METHODS OF CONTROL 251 



media, of Ps. citri, which causes citrus canker. This effect was brought 

 about by inhibiting the growth of and by killing the pathogen. By the 

 use of an antagonistic bacterium, wheat seedlings were protected from 

 infection by H elminthosforiuni sp. (695). In a similar manner, flax 

 seedlings were protected from Fusarium sp. 



A watermelon disease, caused by P hymatotrichwm omnlvoruniy was 

 considerably reduced when certain specific fungi and bacteria were pres- 

 ent in the soil together with the pathogen (91, lOi) j T. Ugnorum was 

 observed to attack and kill the hyphae of Phymatotrichum in culture. 

 The severity of the seedling blight of flax, caused by Fusarium Uni, was 

 diminished when the pathogen was accompanied in the soil by various 

 other fungi (875). The pathogenicity of H. sativum on wheat seed- 

 lings was suppressed by the antagonistic action of Trichothecium 

 roseum, this effect being due to a toxic substance produced by the latter 

 (353). T. Ugnorum prevented infection of wheat (60) by H. sativum 

 and Fusarium culmorum (Table 48). Novogrudsky (646) obtained 

 protection against infection of wheat with Fusarium by inoculating the 



TABLE 48. EFFECT OF TRICHODERMA LIGNORUM ON GERMINATION AND 



GROWTH OF BARLEY INFECTED WITH HELMINTHOSPORIUM 



SATIVUM IN STERILIZED SOIL 



From Christensen (127). 



Notes. Results are based on randomized duplicate pots, each sown with 50 seeds. H, seeds inoculated with 

 a spore suspension of H. sativum; H + T, seed inoculated with H. sativum plus T. Ugnorum; H + SI, 

 seed inoculated with H. sativum and soil with T. Ugnorum. 



soil with the bacteria isolated by Chudiakov (130), provided the bac- 

 teria were introduced simultaneously with the fungus qr preceded it. 

 The role of microbiological antagonism in the natural control of soil- 

 borne fungus diseases of plants has thus been well emphasized (85, 



