22 James Stewart Wiant 



nally isolated. The three most virulent conifer strains, however, gave 

 somewhat greater differences than did the most virulent vegetable strain. 



Turning attention to the results of inoculation tests on vegetable seed- 

 lings, it is apparent from the data in table 6 that greater variation existed 

 in the susceptibility of the different species than was the case with the 

 several conifer species. Pea, cabbage, and sugar beet were distinctly more 

 susceptible than eggplant, pepper, and tomato. 3 



Of the conifer strains tested on vegetables, strain 187 was the most 

 virulent on all species except pepper, on which none of the conifer strains 

 was pathogenic. Strains 156 and 77 were not pathogenic to either pepper 

 or tomato, while strain 167 did not give significant differences over the 

 check in the case of eggplant, pepper, or tomato. Strains 160, 13, and 192 

 were pathogenic only to cabbage and pea. On the basis of these facts, 

 together with that of the extreme differences in average results, it would 

 appear that .strain 187 was the most virulent on vegetables of any of the 

 conifer strains tested, and that strains 13 and 192 were the least virulent. 



Two of the strains from vegetables (196 and 183) were, with one excep- 

 tion, highly virulent on all species of vegetables tested. Strain 1 was highly 

 virulent on cabbage, pea, and sugar beet, but was not pathogenic to 

 eggplant, pepper, and tomato. Strains 195, 184, and 193 were not patho- 

 genic to three suscepts each. The strains from cabbage, sugar beet, and 

 pepper were the most virulent of any of the vegetable strains on the same 

 species of vegetable from which they were respectively isolated. With 

 one exception (strain 187 on sugar beet), the same is true even when all 

 thirteen strains are considered. 



From the tests with the thirteen strains on both conifers and vegetables, 

 it would appear that strains 183 and 196 from vegetables were highly 

 virulent on both groups of suscepts. Strain 187 from white pine was 

 highly virulent on vegetables but not of great virulence on conifers. Strains 

 13, 77, 156, and 160 from conifers were highly virulent on conifers but of 

 low virulence on vegetables. Strains 192 and 167 from conifers, and 193 

 and 195 from vegetables, were of generally low virulence on both groups 

 of suscepts. 



The foregoing relationship is illustrated diagrammatically in figure 1, 

 but, since only the average figures from the last column in tables 5 and 6 

 are plotted, the diagram should be interpreted in the light of the preceding 

 discussion. 



Cultural studies 



Among the numerous strains of Rhizoctonia isolated from conifers, it 

 was observed that marked and more or less constant differences were 

 maintained through successive transfers in tubes of potato-dextrose agar. 

 This led to the study of a number of these strains in petri-dish cultures on 

 cornmeal, oatmeal, potato, potato-dextrose, malt-extract, Czapek's, and 



3 Tests were conducted also with potato. Severe infection occurred with strain 183, and slight infection 

 with strain 193. In view of the extreme variation in soil moisture, the writer does not attacli particular 

 significance to the negative results obtained with the other strains. 



