THE RESISTANCE OF OAT VARIETIES TO STEM RUST 1 
By William W. Mackie, Assistant Professor of Agronomy , University of Cali¬ 
fornia, and Ruth F. Allen, Pathologist, Office of Cereal Investigations, Bureau 
of Plant Industry, United States Department of Agriculture 
INTRODUCTION 
An essential preliminary to breeding for rust resistance is a knowledge of the 
resistant varieties already in existence. An additional requirement, in the case 
of cereal rusts at least, is a knowledge of the physiologic specialization within the 
species of rust under consideration. 
Since the discovery by Stakman and Piemeisel {20) 2 , in 1917, of a second race 
of wheat stem rust, differing in its range of power of infection from the rust 
which they had been using, our knowledge of physiological races in cereal rusts 
has developed rapidly. In 1918 Levine and ’Stakman (8). reported a third race, 
and Melchers and Parker {11) still another. In 1919 Stakman, Levine, and 
Leach {19) distinguished about 12 physiological races and, in 1922, Stakman and 
Levine {16) reported a total of 37. Miss Newton {18), in 1922, made a survey 
of wheat stem rust in Canada and found there 14 of the 37 physiological races 
which are known to occur in the United States. 
The discovery of physiologically distinct races of wheat stem rust led to similar 
studies of other cereal rusts. Hoerner (7), in 1919, working on Puccinia coronata 
Cda., tested many specimens of rust on certain varieties of oats chosen as differ¬ 
ential hosts, and concluded that probably there are four physiological races of 
crown rust of oats. Melhus, Dietz, and Willey {12), in 1922, tested a wide 
range of grass hosts with crown rust from cultivated oats and wild grasses and 
distinguished four physiological races. They state {12, p. 234) that li Avena 
sativa was a common host with varying degrees of infection for all the forms of 
crown rust studied.” 
In 1923 Mains and Jackson {10), in a preliminary report of their work on 
leaf-rust of wheat, Puccinia triticina Erikss., state that this rust consists of at 
least 12 races. Levine and Stakman ( 9), 1923, find “at least two and probably 
three distinct biologic forms of Puccinia graminis secalis .” 
Stakman, Levine, and Bailey {17, 18), in a preliminary report and a later 
report on oat stem rust, Puccinia graminis avenae Erikss. and Henn., state that 
“four, and perhaps five, biologic forms of this rust can be identified by their 
action on Victory (C. I. 1145), White Russian (C. I. 1614), and Monarch Selec¬ 
tion.” 
Parker {15) has published a comprehensive review of the literature on the 
rusts of oats. 
A few extensive tests have been made in the search for varieties of oats that 
are resistant to stem rust. Vavilov {21, 22), working in Russia, inoculated 450 
varieties of wild and cultivated oats with stem rust and found but two that were 
not fully susceptible. Avena sativa var. brunnea Kcke. was graded 2£ (using a 
scale in which 0 represents immunity and 4 complete susceptibility) and Avena 
i Received for publication March 26, 1924. Cooperative investigations between the Agricultural Experi¬ 
ment Station of the University of California and the Bureau of Plant Industry, U. S. Department of 
Agriculture. 
* Reference is made by number (italic) to “Literature cited,” pp. 718-719. 
Journal of Agricultural Research, 
Washington, D. C. 
(705) 
Vol. XXVIII, No. 7 
May 17,1924 
Key No. G-421 
