Nov. 1, 1915 Potato Tuber-Rots Caused by Fusarium Spp. 195 



from that produced by F. coeruleum and other species * * *. In tubers with the 

 jelly -end rot F. orthoceras is often, but not always, associated with such fungi as F. 

 radicicola, Mycosphaerella solani, Sporotrichum Jlavissimum Lk., Rhizoctonia, and also 

 with bacteria. 



Concerning F. radicicola, he says (p. 258): 



It is often isolated from Irish potato, especially from dry tubers affected with stem- 

 end dry rot. Sometimes it is associated with other organisms, but frequently seems 

 to invade the tuber from the stolon before a cork layer has been formed * * *. Its 

 presence in the sweet potato suggests that it might require a higher optimum tempera- 

 ture than its related species, such as F. solani and F. martii. 



F. radicicola, F. oxysporum, F. moniliforme Sheldon, and Rhizoctonia 

 sp., together with various saprophytic fungi and bacteria, were isolated 

 by the writer from jelly-end rots from Watsonville and Moorland, Cal. 

 F. orthoceras, Mycosphaerella solani, and Sporotrichum flavissimum were 

 not obtained from such tubers. 



F. radicicola was most frequently obtained from typical "jelly-end" 

 tubers from California and Idaho. Its ubiquitous nature and its be- 

 havior in all of the inoculation experiments support the view that it is 

 one of the most important causes of this disease. The relation of this 

 species to other tuber rots is discussed in the paragraph on dry-rot. 



The prevalence in California of wilt caused by species of Fusarium and 

 the frequency with which F. oxysporum was isolated from jelly-end rot 

 suggests the fundamental relationship of this species to the disease. F. 

 oxysporum was isolated and identified 24 times from jelly-end rot and 

 stem-end dry-rot tubers from California alone. While often associated 

 with bacteria and fungus saprophytes, in most of these cases it was 

 the only organism secured from the respective tubers which could be 

 regarded as the cause of the condition. It was freqently present in pure 

 culture at the border of rotting and healthy tissues. Whether unaided 

 it produces jelly-end rot under field conditions is not known. A potato 

 tuber from California was diagnosed as ring disease and placed in the 

 incubator. After a period of two months at an average temperature of 

 18.36° C. a typical jelly-end rot had developed. F. oxysporum was the 

 only organism secured from the interior of this tuber at the border of 

 healthy tissue. The inoculation experiments with F. oxysporum sup- 

 port the view that it is capable of producing jelly-end rot. F. radicicola 

 and F. oxysporum were also isolated, though not necessarily in associa- 

 tion, from rot areas on the side of tubers resulting from wounds and 

 lenticel invasion. 



F. radicicola as a cause of stem-end dry-rot was first obtained in 

 August, 1913, from some tubers submitted from Grassfield, Va. Its 

 widespread occurrence in stem-end dry-rotting tubers may be judged 

 from the following distribution: Hermiston, Oreg. ; Watsonville and 

 Sonora, Cal. ; Fallon, Nev. ; Ocean Springs, Miss. ; Jerome, Idaho; Honeove 



