June 23,1923 
Inheritance of Resistance to Puccinia graminis 
983 
Classes of host reaction 
Immune. 
Very resistant 
Moderately resistant. 
Moderately susceptible (appar¬ 
ently resistant in the field). 
Very susceptible 
Resistant to moderately suscep¬ 
tible (apparently resistant 
in the field)^. 
Moderately susceptible to very 
susceptible (probably siiscep- 
tible m the field). 
2. 
(X 
Types of infection ® 
No uredinia developed but definite hyper¬ 
sensitive areas present. 
Uredinia minute and isolated; surrounded by 
sharp, continuous, hypersensitive areas; hyper¬ 
sensitive areas lacking uredinia also may be 
present. 
Uredinia isolated and small to medium in size; 
hypersensitiveness present in the form of 
necrotic areas or circles; uredinia often sur¬ 
rounded by green islands. 
Uredinia midsize; coalescence infrequent; develop¬ 
ment of rust somewhat subnormal; true hyper¬ 
sensitiveness absent; chlorotic areas, however, 
may be present. 
Uredinia large or varying from midsized to large, 
numerous and confluent; true hypersensitive¬ 
ness entirely absent; chlorosis seldom present. 
— Uredinia very variable; apparently includes 
two or more of the o, i, 2, and 3 types of infection 
on the same leaf blade; no mechanical separa¬ 
tion possible; on re inoculation one type of 
uredinia may produce another; infection ill- 
defined. 
-f Uredinia very variable; apparently including 
combinations of one or more of the types o, i, 
and 2, with type 4 on the same leaf blade; no 
mechanical separation is possible; on reinocula¬ 
tion one type of uredinia may produce a dif¬ 
ferent type; infection ill-defined. 
selection oe bioeogic forms 
In October, 1921, about 15 of the 37 known biologic forms were avail¬ 
able. The reaction of Mindum to these forms was known but Kubanka 
No. 8 and Pentad had not been tested. It was hoped that among the 
15 forms some could be found that would react reciprocally on the 
parents of the crosses to be tested. Extensive studies disclosed that 
Forms I and XXXIV reacted reciprocally on Mindum and Pentad. How¬ 
ever, similar success was not achieved with respect to Kubanka No. 8 and 
Pentad. Therefore, only one form. No. XXXIV, was used for the Ku¬ 
banka 8 X Pentad cross. 
The first rust form, designated as Form I, was collected at St. Paul, 
Minn., in September, 1915. When used for the present study it had 
been cultured through approximately 90 urediniospore generations and 
there was no indication of a change in its parasitic capabilities. Mindum 
is decidedly resistant to this form, whereas Pentad and Kubanka No. 8 
are normally susceptible. 
The second form, known as Form XXXIV, was collected by G. F. Puttick 
at Potchefstroom, South Africa, in April, 1921. When it was received 
at the Minnesota station it was evidently mixed with one other form. 
The separation of these forms was not completed until December, 1921. 
Since then more than seven generations have been produced without 
any indication of a change in the constancy of the form. In contrast to 
its reactions to Form I, Mindum is quite susceptible to Form XXXIV 
and Pentad is resistant. Kubanka No. 8 is susceptible to this form. 
® These descriptions of types of infection are based on those given by Stakman and Eevine {25a), 
f Unpublished results of cooperative rust breeding work carried on at the Minnesota station. 
