JOURNAL OF AGMCOLTOtAL RESEARCH 
Washington, D. C., December 22, 1923. No. 12. 
CYTOLOGICAL STUDIES OF INFECTION OF BAART, 
KANRED, AND MINDUM WHEATS BY PUCCINIA 
GRAMINIS TRITICI FORMS III AND XIX 1 
By Ruth F. Allen 3 
Assistant Pathologist, Office of Cereal Investigations, Bureau of Plant Industry , United 
States Department of Agriculture 
INTRODUCTION 
The recent discovery of the specialized or so-called biologic forms of 
wheat stem rust (Puccinia graminis tritici Erikss. and Henn.) and the 
realization of the importance of this discovery in the work of combating 
the disease have led to intensive study of the problem. The knowledge 
that we are not dealing with one uniform fungus, but with numerous 
strains morphologically similar but physiologically distinct, and each 
with its own limited range of power of infection, complicates seriously 
the problem of breeding for rust resistance. 
Stakman and Piemeisel ( 40 ), 3 in 1917, published an account of a 
second strain of wheat stem rust; Levine and Stakman (21 ), in 1918, 
reported a third; and Melchers and Parker (23), in 1918, still another. 
Extensive work then was undertaken by Stakman and his associates to 
“determine the number, characteristics, and distribution of biologic 
forms, as well as their constancy and probable origin.’* In a preliminary 
report, in 1919, Stakman, Levine, and Leach (38) reported about a 
dozen specialized or biologic forms of wheat stem rust; and, in 1922, 
Stakman and Levine (57) reported 37 such forms differing in their power 
to infect the varieties of wheat chosen as differential hosts. They give 
a key by which these specialized rust forms may be identified. 
Specialized forms of stem rust have been under observation too short 
a time to make it certain that they are permanent stable entities, but 
such data as have been reported on the six main subdivisions of Puccinia 
graminis by Stakman and Piemeisel {41) and on the specialized forms 
within Puccinia graminis tritici by Stakman, Piemeisel, and Levine (42) 
and Stakman, Parker, and Piemeisel (59) show that they do not change 
their infecting power readily and are probably to be considered as per¬ 
manent independent strains of the fungus. * 
The students of cereal rusts are agreed that rust resistance is due to 
one or more hereditary factors that behave in Mendelian fashion. Nilsson- 
Ehle (28), Biffen (6), and Armstrong (3), working on stripe rust of wheat; 
Parker (29), on crown rust of oats; Garber ( 13 , 14) and Griffee (i< 5 ), on 
stem rust of oats; and Waldron ( 43 ), Puttick (30), Aamodt (r), Melchers 
and Parker ( 26 ), and Hayes, Parker, and Kurtzweil ( 18 ), in their study of 
the stem rust of wheat, all believe that “the technique of breeding for 
rust resistance is similar to that of breeding for agronomic characters.” 
1 Accepted for publication August n, 1923. Cooperative investigations between the Agricultural Experi¬ 
ment Station of the University of California and the Bureau of Plant Industry, United States Department 
of Agriculture. 
2 The writer makes grateful acknowledgment to Dr. H. B. Humphrey, at whose suggestion the research 
was undertaken, for steady encouragement during the work, and to Professor W. W. Mackie and Pro¬ 
fessor E. B. Babcock for the numerous courtesies extended during the progress of the study. 
* Reference is made by number (italic) to “ literature cited,” pp. 602-604. 
Journal of Agricultural Research, 
Washington, D. C. 
ahu 
571 
VoL XXVI, No. 12 
Dec. 22, 1923 
Key No. G-345 
