Feb. 10,1923 
Genetics of Bunt Resistance in Wheat 
475 
and testing the comparative resistance of their descendants. The inter¬ 
mediate and susceptible segregates indicate multiple factors for resistance 
in both Turkey and Florence, the loss of which renders a given hybrid 
offspring in a later generation a congenial host for the parasite. Such 
factors added together are cumulative in effect, making the segregate 
possessing them immune against all attempts of the organism to set up 
a pathogenic relationship. 
Fortyfold has a dilute or weak resistance that is evidently different 
from that of any of the resistant elements of Turkey, for in the F 3 genera¬ 
tion of Fortyfold X Turkey five out of 593 F 3 families occurred that were 
distinctly more resistant than Turkey, and many occurred more suscep¬ 
tible than Fortyfold. This dilute resistance of Fortyfold showed a value 
of approximately 5 per cent in 1920 when added to the resistance of 
Turkey in the very resistant F 3 families, but in the absence of it and also 
the Turkey resistance, the segregates increased 15 to 20 per cent in the 
amount of bunt produced. High and low selections are being tested in 
the F 4 generation in 1921 to determine the correctness of these assump¬ 
tions, for the data from the F 3 progeny are not as conclusive as one would 
like to have in a characteristic which shows such wide fluctuations as 
bunt resistance. 
Hybrid 128 has no heritable resistance distinct from that of Turkey or 
Marquis, for the F s progeny of crosses with them did not give variations 
exceeding the extremes of the parent types. The intermediates in the F 8 
generation of Turkey X Hybrid 128 indicated that the resistance of 
Turkey was made up of multiple factors, which, when separated, gave 
dilute resistances. The 334 F 3 families of Hybrid 128 X Marquis were all 
very smutty, none having less than 70 per cent of bunt. In the F 4 
generation, however, the high selections gave 10 per cent more bunt than 
the low ones, which indicates a dilute resistance, probably of Marquis, 
that is not affected by the winter weather. Marquis is very resistant when 
spring sown, but this resistance is mostly destroyed or neutralized by the 
winter rest period when fall sown. 
The resistance of Red Russian is not well established in the cross with 
Turkey on account of the small numbers and the unfavorable season in 
which it was tested, but in so far as the F 4 selections tell anything they 
indicate that any resistance it may possess is not different from that of 
Turkey, for none of the segregates were more resistant than Turkey, and 
the most susceptible did not surpass Red Russian in amount of bunt 
produced. The cross between Fortyfold and Red Russian, however, 
prove that the latter has a definite heritable resistance which, added to 
the unlike resistance of Fortyfold, produces segregates much more 
resistant than either parent. That is, the two weak resistances when 
brought together have the effect of a strong resistance comparable to 
that of Turkey or Alaska. The feeble or weak resistance of Fortyfold is 
in accord with that found in the cross between it and Turkey. The 
dilute or feeble resistance of Red Russian has not as yet been corrobo¬ 
rated in other crosses in sufficient detail to warrant discussion. 
From the foregoing evidence, based on seven years’ work with bunt 
resistance in wheat, and with special reference to eight varieties, and the 
inheritance of resistance in the progeny of crosses between them, the 
general conclusions may be summarized as follows: 
The most susceptible wheats, planted under conditions favoring 
maximum infection, produce an average of about 80 per cent of bunted 
