TOBACCO DISEASES A3TD THEIR CONTROL. 



21 



United States show very marked differences in resistance to the dis- 

 ease. White Burley, Maryland Broadleaf, Orinoco, Pryor, and Big 

 Cuban are susceptible. Havana Seed types and Pennsylvania Broad- 

 leaf are of intermediate resistance, and Connecticut Broadleaf, Con- 

 necticut shade-grown Cuban, Little Dutch, and other types are quite 

 resistant. 



A large number of subvarieties or strains ma} 7 be similarly classi- 

 fied, and certain strains of types now growing in some districts are 

 sufficiently resistant to warrant their general use provided their 

 quality is otherwise equally desirable. The testing of the numerous 

 strains on this basis and the development of new resistant strains 

 for the various districts will undoubtedly greatly reduce the damage 

 from this disease, although much experimental work remains to be 

 done before the general usefulness of this measure will be recognized. 

 Up to this time the development of special resistant strains with suf- 



mm 



C - j 







Fig. 14. — Tobacco field affected with brown root-rot. A stunted and uneven growth 

 over the field results from this disease. 



ficient quality to be grown commercially has only been accomplished 

 with Wisconsin Cigar Binder and TVTiite Burley types (fig. 13), al- 

 though much still remains to be done even with these. 



BROWN ROOT-ROT. 



Description. — Brown root-rot is new to tobacco growers, in that 

 it has not been previously described, but it has undoubtedly existed 

 for many years, particularly in the Connecticut Valley. Brown root- 

 rot is also suspected of occurring in Maryland, Tennessee, North 

 Carolina, and Wisconsin. This disease should not be confused with 

 black root-rot. The general aboveground symptoms are the same 

 (fig. 1-i), and the roots are rotted as in black root-rot (PL V, fig. 2), 

 but the two diseases arise from different causes, and therefore the 

 control measures differ in some respects. The signs of the two dis- 

 eases on the root are quite different, black root-rot usually showing 

 many distinctly black roots, whereas in brown root-rot no blackening 

 occurs. Microscopical examination of black root-rot shows the pres- 



