154 Journal of Agricultural Research Voi. iv, No. a 



field soil, i; crown-rot sugar beets from Rocky Ford, Colo., 5; from 

 Garden City, Kans., 2; from Chino, Cal., i; from Kenosha, Wis., i; 

 potato tuber from Carbondale, Colo., i; radish from Madison, i; carrot 

 from Madison, i ; pine seedlings grown at Garden City (contributed by 

 Mr. Carl Hartley, of the Bureau of Plant Industry), 2; and decaying 

 tomato grown on Potomac Flats, Washington, D. C. (contributed by 

 Dr. H. W. Wollenweber (44), of the Bureau of Plant Industry, as R. 

 potomacensis Wollenw.), i. 



The various strains in cultures exhibited no striking differences. Those 

 which did appear are due largely to difference in vigor. The virulence 

 is reduced temporarily by long continuance in artificial culture. Differ- 

 ence in the virulence of the several strains, both when freshly isolated and 

 when rejuvenated, was sometimes noted, and this difference appeared to 

 be quite constant, although it bore no relation to the host which furnished 

 the original culture. For example, one of the two strains most virulent 

 to beet seedlings was secured from the beet root and the other was the 

 form from tomatoes received as R. potomacensis Wollenw. Certain of the 

 strains that were least virulent v/ere obtained originally from sugar-beet 

 seedlings. 



The inoculations were carried out with extreme care, following the meth- 

 ods already described. Every precaution was taken to insure the accuracy 

 of the results, which were uniformly positive. Each strain was recovered 

 and reinoculated into seedlings through from four to six generations. 



The type of disease produced upon beet seedlings is similar to that 

 caused by Phoma betae, but the plants are attacked at a younger stage, 

 and the progress of decay is likely to be more rapid, so that it was neces- 

 sary to exercise considerable care in making inoculations at the time of 

 seeding. In the cases of heavy inoculation few or no seedlings broke 

 through the soil. With lighter inoculation a milder form of damping-off 

 developed, or the disease took the form of root sickness, in which case a 

 relatively large number of plants eventually recovered. The fungus is 

 capable of attacking its host at any time after germination. Inoculations 

 upon older seedlings also gave positive results. Young beets 4 or 5 weeks 

 old were readily killed by inoculations upon the crown when no wound 

 was made. 



DISTRIBUTION OF THE FUNGUS 



The distribution of the fungus is very general, but under field condi- 

 tions damping-off due to Rhizoctonia is far more general in the soils of 

 the semiarid West. Soils brought from western Kansas and Colorado to 

 Wisconsin and placed in pots in the pathological garden yielded a large 

 percentage of damping-off from Rhizoctonia sp., while Wisconsin soils in 

 control pots were practically free from the ravages of this parasite. The 

 fungus has been isolated a few times from the Wisconsin beet fields, but 

 it appears to be of little consequence as a beet parasite under Wisconsin 

 conditions. The reverse is true in Colorado and Kansas, where a majority 



