350 



BULLETIN No. 189 



[June, 



TABLE 8. EELATIVE VIRULENCE OF EHIZOCTONIA INOCULATED ON CARNATION 

 PLANTS AT DIFFERENT TEMPER \TUKES: EXPERIMENT 6 



a Ten plants found infected April 1 ; only three plants died during the months 

 of February and March. 



As can be seen from Table 8, the death rate of the plants inocu- 

 lated on September 1 and October 1 was almost 100 percent. This 

 rate diminished very markedly when the plants were inoculated later 

 in the season, increasing with the plants inoculated during the spring 

 months until with those inoculated on May 1, it had again reached a 

 high percentage. This condition prevailed during the summer months, 

 showing very noticeably the influence of temperature on mortality. 



EXPERIMENT?: INOCULATION OF VARIOUS HOSTS. (SEEDLINGS) OTHER 

 THAN CARNATION WITH VARIOUS STRAINS OF RHIZOCTONIA 



In the preceding experiments all the work was carried on with 

 carnation plants of different ages. It was found that under certain 

 conditions all the strains used could attack these plants, but that the 

 resistance was somewhat increased when the plants were rooted. To 

 determine whether the same results could be obtained with other 

 plants, a number of further experiments were made. 



Small flats (8x10 inches) were disinfected and filled with a mix- 

 ture of sterilized sand and soil suitable for germinating seed. In each 

 flat a 250-cc. soil culture of one of the various strains used was thoroly 

 mixed with the soil, and the whole allowed to stand for several days. 

 The seeds, after a short soaking in formalin (1-150), were sown in the 

 flats, thirty-one in all, care being taken not to plant them too closely. 

 Nine different kinds of seedlings and 13 strains were used in the ex- 

 periment. The results obtained are given in Table 9. 



In the first group of the various hosts, clover proved to be more 

 resistant than alfalfa, while the injury to corn roots was negligible. 

 Of the different strains, the one from clover proved the most virulent, 

 while the one from corn was the weakest (Fig. 19). 



