4 BULLETIN 1410, U. S. DEPARTMENT OF AGRICULTURE 



of the plants is characteristic in fields after sod land in Wisconsin. 

 Often the back furrow in a field is the only place where the tobacco 

 grows normally. (Fig. 4.) 



HISTORICAL REVIEW 



So far as could be ascertained, the disease now referred to here as 

 brown root rot of tobacco was undescribed at the time these studies 

 were undertaken in 1915. One of the writers reported the occurrence 

 of the trouble in 1919 * (11). At that time it was believed that 

 Fusarium might be the causal organism, since apparent mild infec- 

 tion was sometimes obtained with certain strains isolated from dis- 

 eased hosts, although no heavy infection comparable to that occurring 

 in the field was ever found. Clinton (4) in 1920 described a red root 

 rot of tobacco in the Connecticut Valley which is undoubtedly the 

 same as our brown root rot. Although red roots occasionally occur 

 in this disease, it is believed that " brown root rot " is a better clescrip- 



Fig. 3. — Lesions of brown root rot on roots of tobacco (A) and tomato (B). The 

 dark-colored lesions shown here are actually brown rather than black. The 

 localized lesions seem to bear a close relation to the point of attachment of 

 secondary roots 



tive name than " red root rot." Chapman (S) in 1920 also discussed 

 the root-rot situation in the Connecticut Valley and recognized a 

 new disease distinct from black root rot. Neither of these writers, 

 however, showed that any particular organism was definitely asso- 

 ciated with the disease. 



In 1924 the senior writer briefly described the disease in a general 

 treatise on tobacco diseases (12). 



Whether or not this disease has been described on crops other than 

 tobacco can not be definitely ascertained. Occasional references 

 in literature* are to be found to obscure root diseases of various 

 plants, attributed to Fusaria, Rhizoctonia, or other organisms, 

 where the causal agency has not been definitely established. 



The western tomato blight, for instance, ascribed by Humphrey 

 (9) to Fusarium and by Heald (7) to Rhizoctonia, has some simi- 



1 The serial numbers in italic in parentheses refer to "Literature cited," at the end of 

 this bulletin. 



