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 Piithium debarya/n/um in pots of steri- 

 lised soil. 





Pythium strain. 



Num- 

 ber 

 of 

 pots. 



Inoculation 

 method. 



Results. 



Series, experiment number, 

 and host. 



No. 



Initial strain 

 from which it 

 wasreisolated. 



Emerged 



(per5-pot 



unit). 



Damp- 

 ing-off 



after 

 germi- 

 nation 



(per 

 cent). 



Sur- 

 vival 

 (per 5- 



pot 

 unit). 



Series A.— Initial inocula- 

 tions: 



T218 





5 



5 

 5 



5 



5 

 5 



5 

 5 

 5 

 6 

 5 



5 

 5 

 5 



5 

 5 



Agar cultures 



broadcast 



atoneside 



of pot. 



Noinoculum 



do 



Agar cultures 

 at single 

 point in 

 each pot. 



Noinoculum 



Agar cultures 

 broadcast 

 atoneside 

 of pot. 



do 



Noinoculum. 



do 



do 



Agar cultures 

 broadcast 

 atoneside 

 of pot. 



do 



.....do 



Noinoculum 



(») 



1 



74 

 82 



41 



55 

 16 



18 

 90 

 82 

 82 

 14 



3 

 13 



78 



14 



78 



100 





 



28 







81 



89 

 

 

 



72 



67 



67 







72 

 







No. 58, Pinus banksiana. . 



Controls. 

 ..do 





74 







82 





[295 





30 



No. 58, Pinus ponderosa.. 







55 





f258 





3 





..do 





2 





Controls. 

 ..do 





90 







82 









82 





338" 





4 





347 « 





1 





348 a 





4 





^Controla 

 (338 



[Controls. 





78 



SeeiesB. — Reisolatedstrains: 

 No. 62, Pinus banksiana. . 



No. 295 (in P. 

 ponderosa, 

 expt. 58). 



4 



78 



«A different soil used in these pots from that used with strain 2">s and the, first three control units. 



6A11 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. 



