Dec. 9,191 s Seedling Diseases of Conifers 535 



virulence of most of the strains through several years cultivation, indi- 

 cate not only that the cultures used contained only C. vagum, but that 

 most of them contained only a single strain of the fungus. 



On the whole, the limited comparisons possible of initial and reisolated 

 strains, do not indicate any decided increase in virulence on pine seedlings 

 as a result of a single passage through the host. 



CROSS-INOCTJLATIONS 



In Table I is presented evidence of parasitism on three species of pine 

 of strains of Corticium vagum from spruce and sugar beet. In one of 

 these experiments and also in an earlier experiment not included in this 

 table, the original strains from Russian wild olive (Elaeagnus sp.), proved 

 decidedly parasitic on jack pine. The strains 147 and 213, from spruce 

 and sugar beet, respectively, have proved more virulent on the pines in 

 these and other experiments than any of the strains coming originally 

 from pine seedlings. The slight ability of a single strain from Douglas 

 fir to infect pine, referred to earlier, does not prove any specialization of 

 virulence, as some of the strains from pine give negative results on the 

 same species of pine unless given very favorable working conditions. 

 The positive results on Douglas fir with a strain from jack pine in a single 

 very small-scale test made is indication of the lack of any specialization 

 of strains of C. vagum to pine or Douglas fir. 



Inoculations on both jack and western yellow pine have been success- 

 ful with strains from potato tuber and from bean stems, the latter cul- 

 ture being furnished by Dr. M. F. Barrus, who stated that it was from 

 a strain of proved parasitism on beans. The strains from these two 

 hosts were parasitic on pines only under very favorable conditions. 

 Single experiments with strains from alfalfa and carnation supplied by 

 Dr. Barrus, indicated that these were only weakly, if at all, parasitic on 

 pine seedlings. A strain from a sugar-beet root, isolated in eastern 

 Colorado by Dr. F. A. Wolf, of the North Carolina Experiment Station, 

 proved moderately parasitic on pine seedlings, while another strain from 

 the same host and locality showed little, if any, virulence on pine even 

 under the most favorable conditions; All three of the sugar-beet strains 

 had been previously tested by Dr. Edson in his inoculations on sugar- 

 beet seedlings, and found parasitic on them. Cultures from western 

 yellow pine were also tested on sugar-beet seedlings by Edson (7) with 

 positive results. A strain from jack pine, only moderately parasitic on 

 that pine species in inoculation, was found by Dr. Barrus to produce 

 lesions on bean stems, though small and atypical as compared with his 

 own strains. 



The inoculation evidence, as a whole, supports the conclusion that the 

 Rhizoctonia causing the damping-off of pines is the same as the Rhizoc- 

 tonia commonly concerned in the seedling disease of dicotyledons. The 

 same strain can cause disease of both conifers and dicotyledons. Cer- 



