EXPERIMENT STATION BULLETINS. 575 



Name of the Disease. 



This disease, like many others, is known by a number of common names. 

 In Germany it is called ' 'Schorf krankheit' ' and the name ' 'Scab' ' has been 

 applied in this country. * 'Root Rot' ' is a term which is commonly used but 

 sometimes confused with rot due to Sclerotinia and other causes. In choos- 

 ing a common name for a disease one should be selected which will not be 

 confused with other troubles and one which is as descriptive as the nature 

 of the signs permits. The diseased area is not typically scabby, but simply 

 composed of dead tissue. Since this is true, the term "Scab" seems inap- 

 propriate for the trouble as it occurs in America; on turnip rooted celery 

 the term may be more descriptive. The roots constitute one of the chief 

 points of attack and it seems that no term is more fitting than Root Rot. 

 To avoid confusion with other Root Rots of celery we suggest that the dis- 

 ease be called Phoma Root Rot, the causal organism being, as will be shown 

 later, a species of Phoma. 



History and Distribution. 



There is considerable difficulty in determining the approximate time at 

 which Phoma Root Rot first made its appearance as a disease of celery, and 

 in tracing the history of the trouble. While the same disease has been de- 

 scribed by certain European investigators on celeriac in Germany, Holland 

 and France, little has been reported regarding its occurrence in this country. 

 It is hardly probable that this is due to a recent introduction of the patho- 

 gen, or to a limited distribution of the disease. Numerous references in 

 literature to root rots of celery, all presenting much the same pathological 

 aspects, make it more plausible to believe that the disease has been present 

 in certain celery districts for a number of j^ears, and that it is generally dis- 

 tributed through the celery growdng districts of the east and east central 

 parts of the United States. Working as it does beneath the surface of the 

 soil, the true cause of the disease has probably escaped observers because 

 of its rather obscure nature and because of confusion with other diseases. 



Aside from a Phyllosticta leaf spot, reported by Halsted (4), no descrip- 

 tion of anything similar to this disease seems to have been made until Van 

 Hook (7) discovered and described a root rot of celery from the celery dis- 

 tricts of Ohio. He did not identify the organism causing the trouble, but 

 mentioned having found a species of Rhizoctonia in the diseased tissue. 

 He states, however, that he does not believe that Rhizoctonia alone was 

 responsible for the disease. Nor can the WTiter believe that any species 

 of Rhizoctonia had a part other than as a secondary organism coming in 

 after the disease had been initiated by another fungus. In the writer's 

 work with diseased plants, Rhizoctonia has quite frequently been associated 

 with diseased conditions. Inoculations from several typical Rhizoctonia 

 isolations from celery, and with Rhizoctonia solani and a Rhizoctonia from 

 milkweed have given no results which would indicate that any of these forms 

 are markedly pathogenic to celery. Van Hook made inoculations with 

 isolations of Rhizoctonia which he found associated with celery root rot, 

 but was unable to obtain infection. Small celery plants, of course, are 

 sometimes attacked by Rhizoctonia as reported by Peltier* and others, but 

 there is at present no conclusive evidence that any species of this genus 

 causes any serious disease of plants which have passed the seedUng stage. 



* Peltier, G. L. Parasitic Rhizoctonias in America. 111. Agr. Exp. Sta. Bui. 189. 1916. 



