Feb. io, 1923 
Genetics of Bunt Resistance in Wheat 
467 
The season of 1919 was very favorable, and an average of 60 plants per 
row was obtained. Four of the 9 F 3 segregates produced F 4 progeny 
almost as resistant as the resistant parent, Turkey. The range of bunt 
produced by the different F 4 rows indicates that the F 3 row from which 
they were selected was probably heterozygous for resistance in every case, 
the range being from 12.2 to 39.2 per cent, which is a larger fluctuation 
than Turkey. (Ten rows of Turkey were grown in this same series, for 
comparison, the extremes of variation being 0.7 and 6.9 per cent.) There 
was, however, not one of the 144 rows in which the plants did not evidence 
some of the resistance of the Turkey parent, for the susceptible parent, 
Hybrid 128, growing alongside of the F 4 rows contained 98 per cent of 
bunt, whereas the worst F 4 row produced less than 60 per cent. The dif¬ 
ference was even more outstanding in the field than the figures indicate. 
Taxonomically the F 4 rows resembled very closely the susceptible Hybrid 
128, but the bunt-infected plants were very different. Once a plant of 
Hybrid 128 became infected it seldom produced any wheat. Out of 125 
infected plants but 3 produced wheat, while 25 of the F 4 rows produced 
some heads of wheat on every one of the infected plants, and only 11 of 
the 144 F 4 rows contained more than 10 wholly smutted plants. 
The plants in 5 of the 29 F 4 rows from F 3 row No. 1312 were superior 
in yield and quality and were very resistant; they became the progeni¬ 
tors, therefore, of the F 5 selections, five F 4 plants being selected from each 
row. Five plants were also selected from each of two other F 4 rows for 
test in the fifth generation. Thus the individuals of 35 F 5 rows repre¬ 
senting 3 F 3 , and through them 7 F 4 families were tested for bunt resist¬ 
ance in 1920. Ten of these rows—that is, 2 of the F 4 families—were 
selected for susceptibility instead of resistance to see whether the amount 
of bunt could be increased by selection after two generations of selection 
in the opposite direction. The data are summarized in Table VI. 
Table VI .—Distribution of bunt resistance in the F s generation of Turkey X Hybrid 128 
selected from five resistant and two intermediate F 4 families 
F< row No. 
From Fa 
family row 
No. 
Average 
number of 
Fs plants 
per row. 
Bunt in 
F* row. 
Average 
bunt of 
5 Fs rows. 
Range of bunt in Fs 
rows. 
Lowest. 
Highest. 
Per cent. 
Per cent. 
Per cent. 
Per cent. 
1434. 
I3 12 
42 
4-3 
13-3 
3-3 
22. 2 
1470. 
1387 
42 
7* 5 
19. 4 
16. 1 
22. 9 
1425. 
I3 12 
52 
7-9 
9. I 
3- 1 
15-2 
1312 
CQ 
8. 2 
l8. 3 
0. 2 
35. 8 
1445. 
1312 
oy 
4S 
8.5 
O 
14. 7 
7* 
9. I 
18.8 
1426 . 
1312 
60 
27.7 
23. 2 
10. 8 
37-8 
I39 2 . 
1299 
45 
37-5 
48.3 
28. 8 
67.7 
The five plants selected from row 1470 were apparently homozygous 
for resistance in the F 4 generation but lacked an element of resistance 
that Turkey possesses, for they varied around the mean 19.4 per cent 
while Turkey in 1920 varied around the mean 7.6 per cent—the worst 
year for Turkey since the tests began in 1914. The numbers 1426 and 
1392 of Table VI show that they were heterozygous and that suscepti¬ 
bility can be increased by selecting in that direction, for one row was 
within 10 per cent of being as bad as Hybrid 128. 
