Oct. i, 1920 



Fusarium-B light (Scab) of Wheat and Other Cereals 23 



the conditions that actually exist in nature. It introduces into the 

 soil various substances, toxins perhaps, which may have some effect 

 upon the final results. In order to avoid this and to make conditions in 

 the greenhouse as natural as possible, only conidia were employed for 

 inoculation of the soils used for testing the pathogenicity of Gibberella 

 saubinetii on young seedlings. Practically all Fusarium species when 

 grown under proper conditions will produce large masses of conidia, 

 which can be gathered from the substratum with a flat needle, free from 

 any conidiophores or mycelial hyphae, and suspended in a test tube or 

 flask of sterile distilled water. If the conidia are not abundant, a fairly 

 heavy conidial suspension may be obtained by washing the culture 

 with sterile distilled water and straining the water through sterile cheese- 

 cloth. Suspensions of conidia thus obtained were used for inoculating 

 the seed by dipping the seed into it for a few minutes. Spore suspen- 

 sions thus obtained were used for artificially infesting sterilized soil 

 by pouring part of the suspension upon the soil in each of the pots and 

 mixing it with the upper layer of soil. By this method only a com- 

 paratively small number of conidia and only a negligible amount of 

 foreign matter were introduced into the soil. 



In all the soil experiments the soil used was sterilized in pots in 

 an autoclave for 1 hour at 15 pounds pressure. All the seed used for 

 sowing was placed for several minutes in a weak solution of saponin } 

 and shaken hard, the object being to moisten the seed thoroughly and 

 to remove all air bubbles adhering to it. The seed was then soaked for 

 30 minutes in 1 to 1,000 mercuric chlorid solution. Seeds so treated 

 proved to be perfectly sterile on the outside. However, the fungi 

 present in their internal tissues are not affected by this treatment. For 

 this reason, only seeds that were comparatively free from such fungi and 

 healthy in appearance were used for experimental purposes. 



Throughout the work 6-inch and 12-inch pots and garden soil were 

 used for sowing the seed. In each case two pots were planted with 

 infested soil or seed, and one pot was sown as a control. Each 

 experiment was repeated several times. 



Seed of wheat, rye, barley, and oats naturally or artificially infected 

 with Gibberella saubinetii, or planted on sterile garden soil artificially 

 infested with this organism, showed a decrease in germination. In the 

 case of the seed naturally infected, the decrease in percentage of germi- 

 nation is greater and is variable, depending on the degree of infection 

 and percentage of seed infected. This may vary from 2 or 3 per cent 

 to as high as 50 per cent. Artificially infected seed or seed sown on 

 infested soil also shows a lower percentage of germination than the con- 

 trols similarly planted. Here, too, percentage of germination depends 

 on the kind and condition of the seed. It may vary from o to as high as 



1 One hundred cc. of so per cent alcohol and i gtn. of saponin. 



