Feb. to, 1923 
Genetics of Bunt Resistance in Wheat 
4 63 
SEGREGATION OF HYBRIDS 
Only a few of the possible combinations of the eight parent types 
have been made, but the data obtained are sufficient to show the general 
type of the inheritance to be expected, and the crosses described below 
have been tested in sufficient quantities and over a long enough period 
of time to warrant the conclusion that resistance is definitely heritable 
according to the commonly recognized laws of genetics. Three types 
of crosses have been made: resistant X resistant, resistant X suscept¬ 
ible, and susceptible X susceptible. Because a smutted plant is auto¬ 
matically eliminated from further testing, as it produces no progeny, the 
seed for the F x and F 2 generations were not inoculated with spores but were 
treated with formaldehyde instead, so that both susceptible and resist¬ 
ant segregates w r ere saved for the F 3 generation, which was thus the real 
beginning of the test. F x sibs had been saved, however, so that F 2 sib 
rows could be tested with the F 3 ’s the same season, under the same con¬ 
ditions. Thus the parent varieties, the F 2 ’s and the F 3 ’s were all tested 
at the same time in the five crosses that have been carried on in sufficient 
numbers, and under such conditions as to make the results significant. 
The amount of bunt produced per row in the segregates of the F 3 genera¬ 
tions has been arbitrarily put into 10 groups, each class having an ampli¬ 
tude of 10 per cent. The numbers in each class of 10 crosses is given 
in Table IV. 
Table IV .—Number of F 3 rows falling into each class, when the percentage of bunt 
produced from o to 100 is divided into 10 equal parts 
Variety, a 
Number of rows falling into class with average percentage of bunt— 
Total 
number 
of rows. 
5 
15 
i 
25 j 35 
45 
55 
65 
75 
85 
95 
A X T. 
6 
1 
l 
0 | 3 
0 
0 
1 
1 
1 
1 
14 
TXF. 
IOI 
19 
18 ! 12 
6 
6 
3 
2 
1 
0 
168 
T X H. 
T 5 
13 
9 1 23 
28 
33 
1 36 
25 
11 
1 
194 
T X R . 
17 
9 
6 ! 1 
4 
2 
S 1 
2 
0 
0 
42 
Fd X T . 
41 
64 
37 ! 63 ! 
! 97 
104 
! 85 
59 
38 
5 
b 593 
A X J. 
6 
0 
O! 2 j 
2 
0 i 
I 1 
4 
9 
0 
24 
Fd X R. 
1 
17 
34 ! 55 I 
40 ! 
27 ! 
5 
2 
0 
0 
181 
H X M. 
0 
0 
0 i 0 
0 
0 ! 
0 
5 
53 
276 
334 
AXR. 
1 
0 
2 ; 1 
0 
! 1 
1 
2 
1 
2 
11 
A X Fd. 
1 
0 
1 1 3 
2 
1 
! ! 
6 
5 
1 
1 
21 
a T=* Turkey, A=* Alaska, F=* Florence, H= Hybrid 128, Fd—Fortyfold, J=» Jones Winter Fife, M=Mar¬ 
quis, R=Red Russian. 
i> From 42 plants selected at random from an Fs population, which makes these figures really F«'s in which 
there has been no selective elimination of susceptible segregates in earlier generations. 
The average number of plants per row varied in the different crosses 
from 12.6 to 60.8, and more than 60,000 plants were counted in deter¬ 
mining the bunt percentages of the 1,582 rows listed in Table IV. The 
fact that the tests were made during four different years makes com¬ 
parison difficult, in one way; yet it tends to add weight to the general 
conclusions regarding the inheritance of resistance, because of the very 
fact that the different seasons are included. All of the rows in which 
Alaska was one of the parents were grown in 1916. The Turkey crosses 
(except with Alaska and Fortyfold) were tested in 1918. Hybrid 128 X 
Marquis was tested in 1919, and the other two, Fortyfold X Turkey and 
