June 23, 1923 
Rust Resistance in a Marquis-Kota Cross 
1005 
some susceptible types may be obtained from a cross of resistant parents 
is of much interest. . 
Table VI .—Distribution of the F3 seedlings of the cross between Kota and Marquis 
according to types of infection caused by biologic Form XXVII 
Classes of parents and Fa crosses. 
0 
F3 families R. 
12 
F3 families IR. 
F3 families Hi. 
588 
707 
23 
1,312 
22 
F3 families H2. 
F3 families H3. 
F3 families H4. 
F3 families S. 
Marquis H3. 
Marquis IR. 
Q 
Kota Hi. 
16 
Kota H4. 
179 
81I 
Kota R.. 
Types of infection. 
2 — 
2 
2+ 
4— j 4 
1 
1 
. i . 
55 . 
66 
52 
67 
88 
113 
113 
225 
1 
2 
164 
264 
305 
387 
8 
29 
29 
98 
87 
I 
23 
28 
172 
I 
67 
458 
32 
I 
Number 
of plants. 
Num¬ 
ber of 
fam¬ 
ilies. 
1.159 
76 
155 
14 
769 
62 
1,065 
82 
631 
50 
1,715 
139 
496 
39 
104 
8 
639 
55 
17 
I 
212 
15 
811 
59 
Several hybrid F3 families, whose seedling reaction to Form XXVII 
was known, were grown in the rust nursery in 1922, and individual plants 
from various progeny lines were selected. Three such lines, which in a 
previous greenhouse test gave reactions which placed them in the R or 
immune group, were again tested for their reaction to Form XXVII 
for the purpose of checking up the accuracy of the preceding year’s 
study. A total of 16 plants belonging to these three families had type 
o infection and thus were in the immune class. Two lines of the suscepti¬ 
ble group were similarly tested. One gave evidence of breeding true 
for susceptibility while another segregated, giving both susceptible and 
resistant types. If similar results were obtained, the number of families 
in the susceptible group should be decreased from that presented in 
Table VI. 
The Marquis and Kota pots which were inoculated at the same time 
were used as controls on the purity of the biologic forms. In the hand- 
inoculated pots, the killed areas around the uredinia on Marquis were 
much less sharply defined than in the studies made the previous winter. 
In two pots, Marquis seedlings which were inoculated by brushing with 
seedlings infected with biologic Form XXVII were heavily infected with 
rust over the greater part of their leaf surface. The uredinia on these 
heavily infected seedlings were surrounded by sharply defined hyper¬ 
sensitive areas. Apparently environmental conditions may influence, 
to a rather marked degree, the reaction of seedlings to a particular 
biologic form. 
INFECTION UNDER FIELD CONDITIONS 
One of the purposes of the investigation was to determine the possi¬ 
bility of using the greenhouse test as a means of determining those F3 
families having the type of resistance which Kota shows under field 
conditions. While Kota in the field frequently .is heavily infected with 
stem rust, the uredinia do not break out in the same manner as on 
susceptible varieties and are much smaller and often surrounded by a 
43326—23 — “—5 
