Feb. io, 1923 
Genetics of Bunt Resistance in Wheat 
469 
Table VII. Frequency distribution for resistance to bunt in a cross between two varieties 
of wheat , one resistant , the other susceptible 
Variety. 
Year 
tested. 
Bunt in parent 
Numbers falling into classes with average percentage of 
bunt per row of— 
5 
15 
i 
1 ,5 
35 
45 
55 
65 
75 
85 
95 
r 1918 
1919 
[ 1920 
f 1918 
\ *9*9 
l 1920 
1918 
1918 
Per cent. 
O. 5 
7 
Turkey. 
. 6 
II 
2. 4 
c 
Not tested. 
I 
5 
2 
Hybrid 128... 
63. 0 
98. 1 
Not tested. 
2 
1 
3 
1 
3 
TXH F 2 . . . . 
1 
I 
TXHF,. . . . 
.do. 
1. 9 
*5 
12 
13 
10 
9 
7 
2 3 
1 
28 
33 
36 
25 
11 
1 
4.8 
6. 4 
I 
12 
6 
1 
0 
1 
6.6 
2 
10 
1 
txhf 4 . . . . 
1919 
< 7.0 
7* 1 
O 
8 
16 
7 
5 
O 
2 
7 
I 
9. 8 
2 
O 
5 
1 
0 
2 
7 
2 
13-4 
14. 6 
’ 4-3 
7- 5 
7- Q 
4 
2 
0 
I 
2 
6 
3 
4 
2 
1 
3 
1 
2 
2 
txhf 5 . . . . 
3 
0 
2 
1920 
• y 
< 8.2 
1 
3 
1 
27.7 
37- 5 
2 
2 
1 
1 
1 
2 
T 
4 
Table VIII gives the class frequencies of Turkey and Florence in respect 
to bunt resistance as well as those of the progeny obtained from a cross 
between them. An extra column, not given in Table VII, has been 
added to show the rows that were entirely without visible infection when 
harvested. 
It will be seen that the F 2 generation (the constitution of which is 
shown by the F 3 class frequencies) shows transgressive inheritance, with 
the greatest frequency coinciding with the average resistance of the 
parents, if it be assumed that the 72 immune segregates varied in the 
intensity of their resistance in proportion to those in the direction of the 
susceptible end of the table. Such an assumption seems warrantable 
from the records of the F 4 and F 5 generations, for they were more resis¬ 
tant than the parents, and only a trace of bunt appeared in each genera¬ 
tion in a few of the rows. The F 5 generation shows that 19 out of 25 
rows were bunt-free (immune), and their ancestry had been bunt-free 
since the cross was made. Thus, for three generations these selections 
have not produced a trace of bunt, although planted each year under 
conditions favoring maximum infection—that is, the seed was blackened 
with spores. The parents produced an average of 3.5 and 7.1 per cent 
under the same conditions, and other varieities, classed as susceptible 
produced as much as 80 per cent of bunt. 
