PHYSIOLOGIC SPECIALIZATION OF WHEAT STEM RUST IN CANADA, 1919 TO 1955

Abstract

From 1919 until shortly after 1930 the races of wheat stem rust most prevalent in Canada were: race 21, the race group 3-18-36, and the race group 17–29 which again assumed importance from 1940 to 1948. Race 49 was widely prevalent from 1927 to 1932. Race 56, first found in Canada in 1931, was the predominant race from 1934 to 1949. Race 15B, discovered shortly before 1940 and first found in Canada in 1946, was predominant from 1950 to 1955.The influence of changes in the wheat varieties under cultivation on the rust race population is discussed and it is postulated that a north-to-south movement of rust spores late in the summer plays an important part in the perpetuation of races selectively propagated in northern areas.Recently, biotypes of certain races have become important in relation to varieties now in cultivation and new varieties in the course of production. Methods of identification of such biotypes by means of accessory differential hosts are discussed in relation to the breeding or rust-resistant varieties.A brief account is given of races identified from collections of aecia from barberry.