42 



BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 



Pythium can cause the "germination-loss" type of damping-off in 

 Douglas fir as well as in species of Pinus. Of the seeds sown in the 

 control plat 43 produced seedlings which appeared above the soil, 

 while only two seedlings appeared from an equal number of seeds 

 sown in the inoculated plat. 



Altogether, 38 strains, excluding reisolations, have been tested on 

 one or more of the 3 pine species. Strains from both the Pacific 

 coast and the eastern United States and from a number of hosts 

 other than pines were among those used. With the exception of two 

 or three strains from a pine nursery in Michigan, the use of which 

 was followed by so little damping-off as to leave their parasitism 

 uncertain, all of the strains proved parasitic under favorable condi- 

 tions, though some were more virulent than others. The positive re- 

 sults in the 14 successful experiments are based on the comparison 

 of a total of approximately 1,160 inoculated pots with 195 control 

 pots. 



TABLE III. Inoculation experiments with Pythium delmruanum in pots of steri- 

 lized soil. 



a A different soil used in these pots from that used with strain 258 and the first three control units. 



&A11 inoculations with fragments of agar cultures scattered broadcast at one side of the pot, including 

 about one-fourth of its area. Nothing was added to the controls in experiment 62, but sterile agar was 

 added to the controls in experiments 66, 67, and 68. 



