30 



BULLETIN 64, U. S. DEPARTMENT OF AGRICULTURE. 



The sharp differentiation between healthy and diseased varieties 

 in adjacent rows, and other field evidence, indicates that the leaf- 

 roll and curly-dwarf are manifestations of physiological weakness 

 and associated with decline or loss of vigor of the stram. That 

 certain varieties show a greater tendency to such degeneration 

 phenomena is evident, and the still more marked development of 

 these troubles on certain seedlings emphasizes theu- relation to the 

 varietal problem. That many other seedlings in the same field 

 exhibited unusual health and vigor seems convincing evidence that in 

 this seed selection and breeding the way lies open for the complete 

 solution of this problem of leaf-roll control. 



Of 59 of these diseased seedlings selected at random as typical 

 examples in 1912, 29 were affected with leaf-roll and 30 with curly- 

 dwarf; and of 22 selected in 1913, 7 had leaf -roll and 15 had curly- 

 dwarf. The parentage of these is indicated in Table I, for its bearing 

 on the question that will be asked as to whether certain combinations 

 of varieties have a tendency to produce leaf-rolled or curly-dwarfed 



offspring. 



Table I. — Parentage of diseased seedlings. 



Parent varieties. 



Geheimrat Theil X Keeper 



Sophie X Keeper 



President Kriiger X Keeper 



Delaware X Keeper 



Norcross X Keeper 



Gem of Aroostook X Keeper 



Alexander's No. 1 Red X Keeper. 



Bound Pinkeye X Keeper 



Irish Cobbler X Keeper 



Green Mountain X Keeper 



Keeper X Round Pinkeye 



Keeper X Silverskin 



Sophie X Irish Seedling 



Delaware X Round Pinkeye 



Number 

 diseased with- 



Leaf- 

 roll. 



■Curly- 

 dwarf. 



Parent varieties. 



Apollo X Silverskin 



Gem of Aroostook X Round Pink- 

 eye 



Daisy X Keeper 



Early Eureka X Keeper 



Holborn Abundance X Irish Seed- 

 ling 



Alexander's No. 1 Red X Irene. . . 



Manly X Irene 



Garnet Chili X Silverskin 



Irish Cobbler X Irish Seedling... 

 Apollo X Irish Seedling , 



Total. 



Number 

 diseased with- 



Leaf- 

 roU. 



36 



Curly- 

 dwarf. 



A much more detailed analysis of the characteristics of these 

 varieties and their seedlings is really required to answer this question. 

 It is clear, however, that some varieties, like Keeper, are poor parents. 

 A large number of successful crosses with Keeper were secured by 

 Prof. Stuart because it produced an abundance of pollen, but the 

 offspring of these have been so unsatisfactory on account of their 

 tendency to curly-dwarf and leaf-roU that the variety wUl not be 

 used again for crossing. 



From different crosses having the same varieties as parents 

 there have come seedlings, some of which were leaf-roUed and some 

 curly-dwarfed. No. 16472, illustrated in Plate IV, figure 1, is a 

 perfect type of leaf-roU in a cross between Alexander's No. 1 Red and 

 Keeper, while No. 16503, shown in Plate XI, figure 1, is an equally 



