52 U. S. DEPARTMENT OF AGRICULTURE. 



the ring (vascular) tissue of the tuber is seen. White sticky 

 globules of bacteria ooze out from the cut tissues. In this 

 stage, the rot is odorless. 



The rot begins in the vascular ring, causing cavities which 

 are filled with a dirty white, slimy, bacterial mass. Brown 

 rot may be followed by slimy soft rot to which the foul odor 

 of affected tubers is due. 



This rot should not be confused with the ring discolora- 

 tion associated with Fusarium wilt. The latter is most 

 common in northern potatoes, while brown rot occurs only 

 in southern, especially Florida, stock. There is no bacterial 

 exudate from the bundles when a Fusarium infected tuber 

 is cut. 



Infection takes place in the field and the disease is there 

 known as bacterial wilt. The infection proceeds from the 

 affected plant through the horizontal underground stems 

 (stolons) into the tubers which are enlargements of the 

 stolons. Potatoes grown in new soil are most severely 

 affected. 



It is advisable not to plant potatoes in new ground. In- 

 fected stock is subject to decay and should be rapidly dis- 

 posed of. 



Ref. (61). 



POTATO: SLIMY SOFT ROT. 



Cause: Bacteria (Bacillus carotovorus group). 



This disease of the potato belongs to the class of slimy 

 soft rots described elsewhere, but, since it presents itself as 

 a special phase in southern potatoes, a separate discussion 

 is warranted. It is a soft, soupy, exceedingly foul smelling 

 rot. Unless affected tissue is discolored by other causes, 

 there is little change in color, the disintegrated tissue being 

 whitish to yellow. The boundary between the soft disinte- 

 grated and the firm sound tissue is very sharp. As the more 

 or less watery tissue dries, it becomes slimy and finally, 

 when completely dry, a mere chalky white crust. During 

 shipment the skin of affected areas is broken easily, and the 

 slime commonly is smeared over neighboring sound tubers. 

 In car-lot shipments this very materially increases the diffi- 

 culty of sorting. 



Slimy soft rot very generally invades killed tissue. In a 

 wet soil, tubers often become asphyxiated, and the bacteria 

 enter the tuber through scab wounds, through lenticels (the 

 breathing pores of the tuber) , through broken places in the 

 skin, or through diseased stolons. Infection also occurs very 

 generally through bruises received during digging and han- 

 dling. If infected tubers are dug while wet, and scalded by 

 exposure to the hot sun, or if sacked with the wet soil adher- 

 ing, a procedure which may lead to heating or sweating, the 

 rot may progress rapidly from the surface inward through 

 the whole tuber. 



