54 U. S. DEPARTMENT OF AGRICULTURE. 



POTATO: GROWTH CRACKS; SECOND GROWTH. 



Cause : Unfavorable growing conditions. 



Second growth and misshapen tubers are marked by a 

 development of knobs on the tuber's surface, and growth 

 cracks by wide, deep fissures, which are usually covered 

 with the normal protective cork layer of the tuber. 



These malformations occur in all varieties and in all local- 

 ities, but are most pronounced where there is considerable 

 fluctuation in the water supply of the growing crop. 



Second growth tissues are immature, and are subject to 

 peeling, bruising, and freezing injury. These knobs are 

 often broken off, opening a way for Fusarium infection. 



Growth cracks ordinarily are not subject to tuber rot in- 

 fection, whereas mechanical injury such as cuts, splits, and 

 bruises, which are due to careless handling, do not develop 

 the normal layer of cork, hence become infected very 

 readily. 



Tubers showing these deformities are of inferior grade, 

 since a considerable waste in paring is necessitated. 



POTATO: IMMATURITY. 



Cause : Premature death of vines in the field, or prema- 

 ture digging of the crop. 



Immaturity is characterized by excessive peeling of the 

 skin, by a greenish tint under the skin, and by a tendency 

 to excessive wilting and flabbiness during transit and 

 storage. 



This trouble occurs mainly in late varieties of the North 

 and in southern potatoes dug for early marketing. 



Immature tubers are subject to bruising, therefore to 

 Fusarium tuber rot infection, to freezing injury, and to 

 excessive shrinkage if they are shipped in overheated cars. 

 They are not high grade stock and often are bitter in taste. 



POTATO: NET NECROSIS AND INTERNAL BROWN SPOT. 



Cause: Unfavorable field conditions (possibly mosaic 

 disease). 



Net necrosis is characterized by fine, extensive brown 

 streaks which follow the vascular tissues and form a net- 

 work. The discoloration begins at the stem end, where it is 

 often localized ; or, in later stages, it may extend throughout 

 the whole tuber. The discolored tissues are dead. 



It occurs in many varieties, and is favored by poor soil 

 conditions and by hot weather. 



Internal brown spot is marked by brown or yellow re- 

 gions of dead tissues scattered throughout the tuber. The 

 affected regions may be small or large, even one-half inch 

 in diameter. They may be scarce or numerous, and are 

 isolated and not connected as in net necrosis. 



The disease occurs in all varieties, and is favored by an 

 inadequate water supply during the growing period. 



