PHYSIOLOGIC SPECIALIZATION IN OAT STEM RUST IN CANADA FROM 1944 TO 1959

Abstract

Annual physiologic race surveys of oat stem rust have shown that races 1, 2, and 5 predominated in Canada from 1921 to 1944; races 8, 10, and 11 from 1945 to 1952; and races 3, 7, and 12 from 1953 to 1959. The increased prevalence of races 8, 10, and 11 led to increased rusting of the rust-resistant varieties produced in Canada between 1937 and 1941. The increased prevalence of races 3, 7, and 12 was of little economic significance because these varieties were resistant to this group of races. Race 7A, which differs from other cultures of race 7 in being virulent on Rodney, has increased slowly but steadily since its discovery in 1952. Races 6A, 8A, 11A, and 13A which are virulent on Garry as well as Rodney have been found in eastern Ontario and Quebec. The "A" signifies virulence on the variety Rodney which is resistant to earlier cultures of races 6, 7, 8, 11, and 13. Race 6A is virulent on varieties with any or all of the resistance genes A, BC, D, and E. These are the only genes for resistance to stem rust carried by present-day varieties that are grown commercially in Canada. Several sources of resistance to these new and dangerous races have been found. The variety C.I. 4023 appears to have outstanding resistance.