June 23,1923 
Inheritance of Resistance to Puccinia graminis 
989 
of the rust reaction it is immaterial just what the classes are called. In 
the present cross, the Kubanka No. 8 parent is only partially susceptible 
but the Pentad parent is quite resistant. It thus happens that the ranges 
for the two parent varieties overlap somewhat at the x— type of infec¬ 
tion. 
A total of 246 Fg families were tested. The number of Fg plants that 
showed infection was 2,401. The distribution of Fg plants according to 
their types of infection and to the susceptible classes of the various 
families to which they belonged is given in Table IV. The 246 Fg families 
were classified as 9 resistant, 5 near-resistant, 84 heterozygous, 20 near- 
susceptible, and 128 susceptible (PI. I, C-E). Then, one-sixth of the pots 
of Pentad, the resistant parent, were classed other than resistant. Con¬ 
sidering the Fg on this basis, there were 9 plus 1.5, or 10.5 families which 
were as resistant as the resistant parent. The ratio of this number to 
that of the remaining families is 1:22.4. The presence of 2 factors for 
rust reaction fairly satisfactorily explains the results. There was no 
evidence that either susceptibility or resistance was dominant, for the Fg 
plants in the heterozygous class occurred in approximately equal numbers 
on either side of the x— type. 
R^SUI^TS OF INOCUI^ATIONS OF MINDUM X PENTAD Fg FAMILIES WITH 
BIOLOGIC FORM I 
The data obtained with Form I are summarized in Table V. Twenty- 
three control pots of each of the parental varieties were inoculated. Of 
the 274 Mindum plants that were infected, 269 had o and i types of infec¬ 
tion with a killing of the leaf tips in most cases, and 5 had type 4 infec¬ 
tions. These 5 plants clearly were either not Mindum or else they had 
been infected by chance spores of some other form. Accidental infection 
is almost unavoidable where many rust forms are being worked with but 
fortunately it is of infrequent occurrence and usually can be detected. 
Table V .—The reaction of the Fg of Mindum X Pentad to biologic Form I 
Parent varieties 
or F3 families. 
Class of infection. 
Distribution of Fs plants according to the type of 
infection shown. 
Total 
pots of 
parent 
varie¬ 
ties or 
F» fami¬ 
lies. 
0 
I 
2 
x- 
3 
X-b 
4 
Pen tad. 
Heterozygous. 
13 
J 
4 
0 
I 
4 
Do . . 
Near-susceptible.... 
2 
y 
6 
2 
0 
10 
3 
Do. 
Susceptible. 
10 
0 
14 
76 
SJ 
16 
Total.. . 
14 
6 
.... 
25 
0 
17 
29 
76 
23 
Mitidiim. 
Tmmnne. 
236 
I c 
12 
20 
Do 
Near-immune. 
2 
2 
Do . . 
Heterozygous. 
6 
2 
I 
Total 
2 <7 
12 
23 
Immune. 
60"^ 
44 
Do * .., 
Near-immune. 
158 
72 "? 
7 
I 
q 
13 
Do. 
Heterozygous. 
0 
2 
16 
60 
22 
190 
82 
Do. 
Near-susceptible.... 
10 
y 
3 
10 
22 
15 
68 
10 
Do. 
Susceptible. 
6 
72 
2 
165 
17 
Total... 
1 C, 494 
12 
2 
32 
161 
40 
428 
166 
