[newton] wheat stem RUST 157 



Importance of the Present Investigation 



The black stem rust is the greatest source of loss to the wheat- 

 growing industry in Western Canada. So serious is the condition 

 that wheat-growing is no longer profitable in large areas of the Red 

 River Valley, and large numbers of farmers are threatening to abandon 

 their farms unless a solution of the problem is forthcoming. Taking 

 Canada as a whole, the losses in a normal year amount to from 

 5 per cent, to 10 per cent, of the wheat crop. This represents a loss 

 of about eight million bushels in the prairie provinces alone, a loss 

 which in epidemic years may be increased to seventy-five or one 

 hundred million bushels. 



Every wheat grower realizes his great annual loss, but he is 

 powerless to prevent it. The weapons of the fruit grower, spraying 

 and dusting, cannot be employed, not only on account of their pro- 

 hibitive cost, but also because of the mechanical injury spraying 

 machinery would cause to the maturing wheat crop, as rust does not 

 appear on the plants until the heads are well advanced. 



The farmers' only hope lies, then, in the production of rust- 

 resistant varieties of wheat. Not only would such wheats largely 

 eliminate one of the most important causes of unfavourable fluctuation 

 in yield, thus greatly increasing the financial returns, but they would 

 also contribute in an important degree to the safety and stability of 

 the wheat-growing industry. 



The problem is, however, complicated by the discovery of the 

 occurrence of more than one biologic form of stem rust. This dis- 

 covery was not only of scientific interest but had a direct bearing 

 on the breeding of grain for rust resistance. It showed why "few 

 varieties seem to be universally resistant" (Freeman and Johnson, 

 24), and explained the diverse opinions of workers in different localities 

 as to the relative rust resistance of certain wheat varieties. 



A study of biologic forms must precede the breeding of rust- 

 resistant wheats. As Stakman has pointed out, "methods of breed- 

 ing for rust resistance must be changed fundamentally. The breeder 

 must know and work with those forms of rust which occur in the 

 region for which his new variety is intended, and even then breeding 

 must be very largely a regional or even a local problem." 



With the numerous forms of stem rust on wheat present in the 

 United States, the question naturally arose, "Did biologic forms of 

 stem rust occur in Canada?" Until the present investigation was 

 undertaken, no specific work had been done along these lines, although 

 observations made by Dr. W. P. Thompson of Saskatchewan 



