BUST RESISTANCE IN WIIsTTER-WHEAT VARIETIES. 25 



under various temperature conditions and at various stages of 

 development of the plant. The work has been done by different 

 persons at different agricultural experiment stations and always 

 with the same results. The only visible evidence of infection in 

 the seedling stage has been the occasional appearance of very indefi- 

 nite, scarcely visible, whitish flecks, generally less than 0.1 millimeter 

 in diameter. These indefinite flecks are not similar to the areas or 

 flecks occurring on the seedlings of the resistant emmers and durums 

 (PI. XI, fig. 2, C) and are very much less conspicuous. In this 

 respect these three varieties of winter wheat are distinct in their 

 behavior. 



The behavior of Kanred, P1066, and P1068 in the nursery and 

 field is not greatly different from that in the greenhouse. Table 1 

 shows that these varieties had very low percentages of stem-rust 

 infection, varying in 1916 and 1917 from a trace to 10 per cent. 

 In 1915 the percentages recorded were higher. In view of present 

 knowledge of the existence of several distinct biologic strains of 

 wheat-stem rusts (38, 39, 40, 4^), this rather heavy infection very 

 probably was due to the use of one or more biologic strains of stem 

 rust similar to, if not identical with, the one recently described by the 

 writers {SO). 



When mature culms of the three resistant varieties were inoculated 

 in the greenhouse with cultures of Puccinia graminis tritici, a response 

 on the part of the host to the rust infection was only occasionally 

 visible. Slightly yellowish or brownish white minute dead areas 

 were sometimes vaguely visible, indicating that infection had 

 occurred but that the organism had ceased to develop. 



The results reported in this bulletin establish the fact that Kanred 

 and two other very similar pure lines of hard red winter wheat are 

 resistant to certain biologic strains of black stem rust. 



More recent studies {25, 30, 4-1) have shown that these varieties 

 are not resistant to all the known strains of stem rust. Extensive 

 field observations made in 1919 and 1920 have indicated, however, 

 that Kanred is much less severely injured by most of the stem-rust 

 strains occurring in Kansas than are Turkey and Kharkof, the other 

 varieties commonly grown. Reports from Wisconsin, Alabama, 

 Nebraska, New York, Illinois, Missouri, Iowa, California, and New 

 South Wales (Australia) indicate that these three varieties have 

 shown resistance to stem rust, while the Minnesota and the South 

 Dakota agricultural experiment stations report them rather severely 

 rusted, although in South Dakota Kanred showed less rust than 

 Turkey. Because of the existence of distinct strains of stem rust 

 it is probable that the behavior of these varieties will vary in different 

 reasons and in various sections of the country. 



