DAMPING-OFF IE" FOREST NURSERIES. 65 



rious strains of Botrytis, both from conifers and from other hosts 

 (the latter supplied by the departments of plant pathology of the 

 California and New York (Cornell) Agricultural Experiment Sta- 

 tions) , have already yielded confirmatory evidence of the parasitism 

 of B. drier ea. 



While a considerable number of fungi have been considered in the 

 foregoing, it is entirely possible that there are still parasites which 

 have received no consideration and that some of them may perhaps 

 be important. The moist-chamber method of culturing parasites 

 for isolation yields only those which produce spores readily; the 

 planted-plate method is not well adapted to the isolation of slow- 

 growing fungi or bacteria. It is suggested that in further culture 

 work with damped-off conifers an attempt be made to secure slow- 

 growing organisms by dilution plates of teased-up fragments of 

 recent lesio*ns. 



RELATIVE IMPORTANCE OF THE DAMPING-OFF FUNGI ON 



CONIFERS. 



The relative importance of the different damping-off parasites is 

 something that has not been thoroughly investigated for any host. 

 The most information on this point is that given by Busse, Peters, 

 and Ulrich (22) for sugar beet. In this case they find the special- 

 ized Phoma betae distinctly the most important, with Pythium de- 

 baryanum second and Aphanomyces levis third. 



Peters (100) apparently considered Ehizoctonia unimportant as 

 a cause of beet damping-off. The opposite was indicated by a small 

 number of cultures by Edson (38) from beet seedlings on Kansas 

 and Colorado soil. These yielded more Corticium vagum than any 

 other parasite and no Pythium at all. Johnson (81) states that 

 most of the damping-off of tobacco seedlings is due to Pythium 

 debaryanum and Corticium vagum. Atkinson (1), speaking for 

 cotton in Alabama, and Sherbakoff (127, p. xcv; 128; 129), speak- 

 ing for truck crops in Florida, make Corticium vagum the impor- 

 tant damping-off parasite, with P. debaryanum negligible. Home 

 (oral communication) found the same situation in tobacco seed 

 beds in Cuba. Atkinson (3), in an article on trees, held that many 

 of the cases of damping-off attributed to P. debaryanum are in real- 

 ity due to C. vagum. Peltier (98, pp. 336-337) has reported Ehi- 

 zoctonia solani as the cause of damping-off of a large number of 

 plants, recording his observation of the damping-off of seedlings of 

 nearly 50 species of miscellaneous genera and cuttings of 13 different 

 species, all of which he attributes to the Ehizoctonia. He does not 

 state whether in this case he used diagnostic methods likely to de- 

 tect Pythium debaryanum if it had been present. 

 19651°— Bull. 934—21 5 



