26 
Journal of Agricultural Research 
Vol. XXIX, No. 1 
Table XVIII.—- Height of 726 F 3 plants of the Kota-Hard Federation cross, in 
comparison with the parents, when grown at Mandan, N. Dak., in 1923 
Frequency distribution by height classes 
(inches) 
F 3 hybrid 
Hard Federation 
Kota 
Number 
. . 
Percent¬ 
age 
Number 
Percent¬ 
age 
Number 
Percent¬ 
age 
18-.. ..... .. 
18 
2.5 
35 
36.8 
21 ______ 
174 
24.0 
58 
61.1 
24 .. .. ... 
268 
36.9 
2 
2.1 
27... 
170 
23.4 
4 
5.3 
30 ..... 
74 
10.2 
32 
42.7 
33 ... ... 
20 
2.8 
38 
50.7 
36 ..... 
2 
.3 
1 
1. 3 
Total... 
726 
100.1 
95 
100.0 
75 
100.0 
A severe June drought occurred at 
Mandan, causing a shortening of both 
hybrids and parents. Rains early in 
July enabled late varieties or late- 
sown wheat to reach a more nor¬ 
mal height. This droughty condition 
.affected the F 3 results. It will be noted 
that the majority of F 3 hybrids tend 
to the shortness of the Hard Federa¬ 
tion parent, which is the reverse of the 
F 2 results. It is concluded that tall¬ 
ness may be partially dominant but 
due principally to heterosis and easily 
influenced by different environmental 
conditions. As most of the selections 
were as early as Hard Federation, the 
desired increase in height is being 
obtained in some cases even under 
conditions of severe drought. The 
average height of the F 3 selections was 
25 inches, that of Hard Federation 20 
inches, and that of Kota 31 inches. 
The hybrids were more than twice as 
variable as the parents, the coefficient 
of variability for the hybrids and parents 
being as follows: 
F 3 hybrids_ 13. 365 ±0. 237 
Hard Federation_ 6. 823 ± . 334 
Kota_ 5. 624 ± .310 
STEM-RUST INFECTION 
Resistance to stem rust, Puccinia 
graminis tritici, is the most economi¬ 
cally important physiological character 
studied in this cross, as severe losses 
from stem-rust infection are common 
in the northern spring-wheat section. 
Several investigators, both plant 
breeders and plant pathologists, are 
studying resistance to this disease. 
Hayes and Stakman (21 ) have reviewed 
the investigations of these workers. 
Stakman and Levine (33) have shown 
that there are 37 physiologic forms of 
stem rust of wheat which are identified 
by their parasitic action on 12 differ¬ 
ential hosts. This is thought to account 
for much of the disagreement in field 
results. Aamodt (2), in a study of 
Kanred X Marquis, found Kanred 
immune to several of these specialized 
forms and susceptible to others. In 
greenhouse studies with the immune 
strains, immunity was found to be 
dominant. There were no interme¬ 
diates. The experiment indicated that 
the reaction to the several forms was 
inherited as a unit. Hayes and 
Aamodt (20) have shown under field 
conditions that in the Marquis-Kota 
cross the resistance of Kota was reces¬ 
sive. No definite genetic ratio was 
determined, resistant F 3 families occur¬ 
ring in the proportion of about 1 to 
7.73. The resistant strains were as 
resistant as Kota. 
In the Kota-Hard Federation cross, 
the present study in the field also 
shows susceptibility to be dominant 
and resistance recessive. At St. Paul 
the plants were inoculated with nine 
different specialized forms of stem rust 
common to the northern spring-wheat 
region. At Mandan, N. Dak., natural 
infection occurred and it is not known 
how many forms of rust were present 
there. No rust occurred at Davis, 
Calif. Abundant infections were ob¬ 
tained at both St. Paul and Mandan, 
but the injury was not great at either 
place. Infection at Mandan was a 
little more abundant than at St. Paul. 
Rust notes were taken on individual 
plants at both points. The data are 
given in Table XIX and graphically 
shown in Figure 5. Extreme degrees of 
infection obtained on F 2 plants grown at 
Mandan are shown in Plate 3. The 
infection on the resistant plant was 
recorded as 2 per cent and that on the 
susceptible plant as 95 per cent. De¬ 
grees of infection intermediate between 
these two extremes were obtained on 
the hybrid material at both points. 
