1014 
Journal of Agricultural Research 
Vol. XXIV, No. 12 
of oats, belonging to 6 different species of the genus Avena, namely: 
A. brevis Roth., A. nuda L., A. sativa L., A. orientalis L., A. sterilis L., 
and A. strigosa Schreb. 
It was found that definite preliminary results were likely to be obtained 
by using only three varieties of oats, viz: Victory, White Tartar (White 
Russian) and Monarch Selection (of Etheridge). All collections were run 
to Victory and White Tartar (White Russian). Victory was completely 
susceptible to all of the strains tried. White Tartar was very highly 
resistant to most of them, while Monarch Selection, which was inoculated 
only with the collections made in 1921 and 1922, was extremely suscep¬ 
tible to some of these collections and practically immune from others. 
Attempts then were made to find forms of stem rust which would infect 
the White Tartar variety heavily. This was achieved with rust material 
procured from Europe and Africa. 
Victory was completely susceptible to. White Tartar very resistant to, 
and Monarch Selection (of Etheridge) practically immune from, a form 
collected by Mr. Fred Griffee at St. Paul, Minn. This is designated 
hereafter as Form I. 
A form of rust collected by Prof. Wallace Butler at San Marcos, Tex., 
infected Victory normally, developed only lightly on White Tartar, but 
produced targe, vigorous uredinia on Monarch Selection. These results 
were confirmed by repeated inoculations, and clearly indicated the exist- ^ 
ence of a second biologic form of Puccinia graminis avenae, as it was 
capable of infecting Monarch Selection normally, which the form col¬ 
lected by Mr. Griffee could not infect. This is designated as Form II. 
A rust strain sent by Mr. G. F. Puttick from Potchefstroom, Union of 
South Africa, infected Victory normally. White Tartar moderately, and 
Monarch Selection normally. This undoubtedly was a third form and 
is hereafter called Form III. 
Finally, Stakman found a form at Upsala, Sweden, which infected 
White Tartar just as heavily as it did Victory and Monarch Selection. 
This, then, was a fourth form,® designated as Form IV. 
Table I summarizes the action of these four forms on the varieties of 
oats which served as the differential hosts. 
It is quite evident from Table I that Form I (PI. 2, A) infects Victory 
normally, but develops only lightly on White Tartar (White Russian) 
and exceedingly lightly on Monarch Selection. Form II (PI. 2, B) 
infects Victory and Monarch Selection heavily, but attacks White Tartar 
only lightly. Form III (PI. 3, A), like Form II, attacks Victory and 
Monarch Election very heavily and in addition attacks White Tartar 
moderately. Form IV (PI. 3, B) infects all three varieties very heavily. 
Repeated inoculations have been made and the same results have been 
obtained consistently. 
Two different forms were isolated from a single collection several times. 
In some cases the X type of infection described for wheat rust (9, p. 5) 
also developed on oats. Several strains produced this X type of infec¬ 
tion on Monarch Selection, thus indicating the probable existence of a 
fifth biologic form which infects Victory very heavily, White Tartar only 
lightly and Monarch Selection heterogeneously (PI. 4). There are now 
known, therefore, at least four, and probably five, biologic forms of 
Puccinia graminis avenae which produce different reactions on certain 
varieties of Avena spp. 
® Proper disposition is being made of the spore material of the South African and Svfedish forms, as they 
have not yet been found in the United States. 
