GENERAL METHODS OF CONTROL 305 



rial, the disease could be checked j the toxin was more or less specific for 

 the particular organism. Certain bacteria commonly found in soils were 

 shown (306) to have a deleterious effect on the growth, in artificial 

 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 elminthosforium sp. (729). In a similar manner, flax 

 seedlings were protected from Fusarium sp. 



A watermelon disease, caused by Phymatotrkhum omnivoruniy was 

 considerably reduced when certain specific fungi and bacteria were pres- 

 ent in the soil together with the pathogen (105)} T. lignorum was 

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

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

 diminished when the pathogen was accompanied in the soil by various 

 other fungi (901). 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 

 (359). T. lignorum prevented infection of wheat (63) by H. sativum^ 

 and Fusarium' culmorum (Table 52). Novogrudsky (685) obtained 

 protection against infection of wheat with Fusarium by inoculating the 

 soil with the bacteria isolated by Chudiakov (143), provided the bac- 

 teria were introduced simultaneously with the fungus or preceded it. 



TABLE 52. EFFECT OF TRICHODERMA LIGNORUM ON GERMINATION AND 



GROWTH OF BARLEY INFECTED WITH HELMINTHOSPORIUM 



SATIVUM IN STERILIZED SOIL 



From Christensen (141). 



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. lignorum; H + SI, 

 seed inoculated with H. sativum and soil with T, lignorum. 



