138 Journal of Agricultural Research voi. iv, no. 2 



SEED TREATMENT 



Sugar-beet seed is quite universally infected with parasitic fungi. It 

 was therefore necessary to devise some method of freeing the seed from 

 infection before inoculation experiments could be successfully conducted. 

 Among the substances tried were hydrogen peroxid, hydrochloric acid, 

 sulphuric acid, formalin solution, formaldehyde vapor, and hot water. 

 Peroxid solution (6 per cent) was used for varying periods up to one hour. 

 The seed was then sown in sterilized soil and watered with distilled 

 water. The pots were protected from infection, but damping-off was in 

 no degree checked, and Phoma betae was invariably isolated from the 

 diseased seedlings (PI. XVII). 



Hydrochloric acid was employed in various concentrations up to a 

 specific gravity of 20° B. for 15 minutes. The seed was then rinsed in 

 sterile water, followed by lime water, which in turn was followed by 

 sterile water. This treatment was without effect upon the vitahty either 

 of the seed or of the fungi. 



Sulphuric acid was used in various strengths up to full concentration 

 for one hour. The treated seed germinated strongly and from 24 to 48 

 hours earlier than the untreated control, but there was no decrease in 

 the amount of damping-off. 



Formalin solution was employed up to concentrations of 2 per cent of 

 formaldehyde for various intervals up to one hour. This seriously injured 

 the viability of the seed, but afforded no check to the disease. The 

 results with formaldehyde vapor are inconclusive, since they lack uni- 

 formity. 



"The method finally settled upon for experimental work was one em- 

 ployed by Peters (7, p. 273-274), which consists of heating the seed in 

 water at 60° C. for 10 minutes, promptly drying superficially upon filter 

 papers, so as to prevent germination, and after an interval of 24 hours 

 heating a second time for 10 minutes at 60° C. The seed treated in this 

 way and sown in sterilized soil, watered with sterile water, and protected 

 from outside infection remained practically free from disease. Not more 

 than one seedling in three or four hundred was infected with Phoma 

 betae. The percentage of germination is unquestionably lowered by this 

 treatment, but it is the only method tried by which inoculation experi- 

 ments could be controlled. It does not appear to be a method which 

 could be applied on a commercial scale. 



METHODS OF INOCULATION 



Inoculation experiments were carried out in pots either in the labora- 

 tory or usually in the greenhouse, using seed treated in the manner just 

 described, and with soil sterilized by heating three or four hours in the 

 autoclave under a pressure of from 12 to 15 pounds on two, or usually 

 three, consecutive days. Inoculations were made in the soil or upon the 

 seed at the time of sowing, except when otherwise stated. Various 



