60 U. S. DEPARTMENT OF AGRICULTURE. 



tuber is gouged by rubbing against the container or by being 

 walked upon. In either case, the result is a loss of water 

 by the injured cells, leaving a solid, grayish, starchy deposit. 

 At times this deposit is black, and externally the bruised 

 areas often appear black. These types of bruising are very 

 common in potatoes grown under irrigation. The injury 

 due to gouging is more severe than peeling or feathering 

 though it usually is due to the same causes. 



Often potatoes are bruised or crushed by impact or by 

 the weight of the load. In addition to the injuries above 

 described, impact or pressure may cause symptoms which 

 may be wholly internal or may be indicated externally only 

 by small, slightly sunken spots. At times these internal in- 

 juries resemble those due to freezing and consist of small 

 pockets of grayish, starchy masses, the remnants of rup- 

 tured, dried-out cells. 



Most of the cuts in potatoes are caused by digging imple- 

 ments, and by the pernicious custom of handling potatoes 

 with steel shovels or forks. Cuts may be broad and shallow 

 or very deep. 



If the cut or bruised tissue has an opportunity to dry out 

 rapidly the injury may be sealed by a grayish granular 

 deposit of starch, and later by a brown layer of cork. Very 

 often, however, especially under moist conditions, Fusarium 

 gets a foothold before the bruised or cut tissue is healed. It 

 may also enter through subsequent breaks in the dry starch 

 layer. In very hot weather, especially in southern potatoes, 

 slimy soft rot gets a start in bruises and cuts. Shallow, 

 broad, or smooth cuts are less subject to infection than those 

 which are deep and ragged. 



Potatoes often are fractured by pressure or by impact. 

 Careless throwing about of potatoes, heavy loading, walking 

 upon potatoes, and similar rough treatment, are responsible 

 for these fractures or so-called splits. These may be visible 

 externally or they may be wholly internal. In either case 

 the surfaces of the fracture are lined with a deposit of starch 

 or a brown layer of corky tissue. At times freshly dug 

 potatoes develop splits if they dry out too rapidly. 



Bruised, cut, or split potatoes are suitable for food, though 

 the injuries necessitate very appreciable losses in paring. 

 Their presence, however, lowers the market value of a 

 shipment. 



These mechanical injuries generally are ports of entry for 

 fungi and bacteria which cause tuber rots. In most cases of 

 Fusarium tuber rot, the infection starts in such injuries. In 

 the early part of the shipping or storage period, it is impos- 

 sible without a cultural test to determine whether a me- 

 chanical injury will remain merely an injury or develop a 

 tuber rot. However, as the season progresses, the rot symp- 

 toms become more pronounced. 



This type of injury with its frequently disastrous conse- 

 quences could be prevented if it were constantly borne in 



