2 BULLETIN 195; U. S. DEPARTMENT OF AGEICULTUKE. 



material variation between the total potato production of the two 

 countries. 



The modern tendency toward the development of potato-growing 

 centers in widely separated sections of the United States, as, for ex- 

 ample, Aroostook County, Me., the Norfolk and Eastern Shore 

 trucking regions of Virginia and Maryland, the Red River Valley of 

 Minnesota and North Dakota, the Kaw Valley of Kansas, the Greeley 

 and Carbondale districts of Colorado, and the San Joaquin and Sac- 

 ramento Valleys of California, has created a demand for varieties 

 of potatoes especially adapted to cultivation in those sections. 

 This condition, coupled with the presence of numerous diseases of 

 the vines and tubers, from which frequent and oftentimes severe 

 losses have resulted, has caused many inquiries to be made regarding 

 the possibility of developing new varieties or strains possessing 

 certain specific qualities not embodied, at least to the same degree, in 

 those varieties now under cultivation. 



This demand upon the plant breeder has served to emphasize the 

 necessity, as well as the desirabiUty, of attempting to develop, 

 either through breeding or selection, new varieties or strains of pota- 

 toes which shall possess a greater degree of resistance to the parasitic 

 fungi which now prey upon the plants and tubers. Another fruitful 

 field of investigation well worth the attention of the plant breeder is 

 the development of potato varieties that are better adapted to certain 

 sections of our country. These adaptational characteristics may be 

 either earliness or lateness, drought resistance or heat resistance, or an 

 ability to succeed in heavy or in light soil; they may be productive- 

 ness, shape of tuber, quaUty of tuber, starch content, or, in fact, any 

 distinct quaUty which would make a variety especially desirable for 

 cultivation in a given locality. 



POTATO BREEDING AND SELECTION DEFINED. 



In order that there may be no confusion in the mijid of the reader 

 as to what is meant in this bulletin by the term '^ breeding," the writer 

 has thought it best to make a clear-cut distinction between "breeding" 

 and ''selection." 



Breeding is here employed in the sense of sexnal reproduction. 



Selection implies, in the case of the potato, the isolation and 

 asexual propagation of desirable strains or types. 



Breeding can only be successful when it goes hand in hand witJi 

 selection. Selection, on the other hand, is not dependent upon breed- 

 ing for results. 



LIMITATIONS OF BREEDING AND SELECTION. 



Broadly speaking, the limitations of breeding are not simply those 

 found within the confines of our cultivated varieties of potatoes, but 

 those embraced by the whole range of the tuber-bearing solanums. 



