The Rhizoctonia Damping-Off of Conifers 5 



conclusively demonstrate the pathogenicity of Rhizoctonia on conifers, and 

 on the basis of inoculation tests point out marked differences in virulence 

 between the strains used. Together with the work of Edson (1915) with 

 sugar beets, and that of Edson and Shapovalov (1918) with potatoes, the 

 results indicate that strains pathogenic on conifers are likewise capable of 

 attacking angiosperms, and vice versa. Hartley (1921) concludes there- 

 fore that the strains from conifers are identical with the common Rhizoc- 

 tonia solani Kiihn, the perfect stage of which is Corticium vagum B. & C. 

 (Burt, 1926). 



It is apparent from the literature (Duggar, 1915; Peltier, 1916; Rosen- 

 baum and Shapovalov, 1917; Edson and Shapovalov, 1918; Matsumoto, 

 1921; Briton-Jones, 1924, 1925; Gratz, 1925; K. S. Thomas, 1925; Van 

 der Meer, 1926) that marked differences exist between various strains of 

 this common pathogene. The evidence presented by Rosenbaum and 

 Shapovalov (1917), Matsumoto (1921), Gratz (1925), and Van der Meer 

 (1926), suggests the existence of special forms within the species. Duggar 

 (1915) and Matsumoto (1921) each report a single fungus which differs 

 sufficiently from the others studied to possibly merit specific rank. Matz 

 (1921), working with strains of Rhizoctonia found on subterranean plant 

 parts, describes three new species which occur along with R. solani. From 

 the work of Briton-Jones (1924), however, it would appear that the differ- 

 ences used by Matz in separating species are not greater than those between 

 several cultures of the same strain of R. solani grown under different 

 conditions. Most of the comparative studies on Rhizoctonia have been 

 made with strains isolated from angiosperms. 



Inoculation tests on coniferous seedlings with a number of miscellaneous 

 fungi are reported in the papers of Hartley, Merrill, and Rhoads (1918) 

 and Hartley (1921). More recently, Rathbun-Gravatt (1925) has brought 

 together the results of direct stem-inoculation tests with more than one 

 hundred different strains of fungi. Of these the author finds a few species 

 of Fusarium and certain strains of Corticium vagum, Pythium debaryanum, 

 Pythium aphanidermatum (Eds.) Fitz., and Botrytis cinerea Pers., capable 

 of causing damping-off. The last three organisms, together with Fusarium 

 sporotrichioides Sherb., are the most virulent. Further tests with this 

 method are reported by Eliason (1928). 



In summary, then, Phytophthora fagi and Fusarium spp. are reported 

 as the chief causal organisms in Europe, and Pythium debaryanum, Corti- 

 cium vagum, and Fusariu?n spp. in the United States. Hartley (1921) 

 presents considerable evidence in support of his conclusion that these 

 last -mentioned fungi are equally important as the chief causal organisms 

 involved in the darnping-off diseases of conifers in this country. 



Many investigators have concerned themselves with attempts to control 

 damping-off of conifers. While various methods have been employed, 

 the most satisfactory results have been obtained through chemical treat- 



