Feb. 10,1923 
Genetics of Bunt Resistance in Wheat 
457 
tissue near the surface of the earth. With the approach of summer the 
stems elongate rapidly, the seeds develop, and the plant dies. The 
vegetative stage is completed in from one to eight months, depending 
upon temperature and variety. 
The vegetative period exhibits some interesting variations. A funda¬ 
mental varietal agronomic difference of great practical importance, which 
is entirely ignored in most taxonomic nomenclature, is the habit of 
growth during this vegetative period that distinguishes winter and spring 
wheats. A typical winter wheat, in the north temperate zone, will not 
head out or produce grain if planted in the spring. It remains as a green 
grass clump all summer and dies the following winter. If it is pastured 
or the leaves frequently cut off during the summer, it may live through 
the winter and the following summer head out and produce a normal crop 
of grain. Spring wheat, planted in the spring, passes through the vege¬ 
tative stage in a few weeks and then the culms rapidly elognate, the head 
develops, and a normal crop is produced. If both are planted in the fall, 
the winter wheat lives through the freezing and thawing of a severe winter 
and produces a normal crop the following harvest under conditions in 
which the spring variety would winterkill. The time required from 
flowering to the maturing of the grain varies greatly with the changing 
climatic conditions. High temperatures, bright sunlight, and strong 
winds favor rapid maturation. Cool, cloudy weather with little wind 
favors the maximum length of time between flowering and maturity. 
The elongation of the stems, flowering, and fruiting are completed in from 
30 to 60 days or longer, depending upon weather conditions. 
Most of the cultivated wheats are of the species Triticum vulgare , but 
in certain districts the durum and club wheats predominate. Durum 
is produced in the Dakotas and western Minnesota principally, and the 
club area is confined, for the most part, to the Pacific Northwest. 
Many investigators have classified comparative susceptibility to 
disease according to genera and species. (Jaczewski ( 18 ), Carleton (<£), 
Freeman and Johnson (12), Stakman (52), Kirchner (22), and Reed (42).) 
For wheat they have shown that einkorn is generally resistant to all 
rusts and mildews. The durums, polish, poulard, and some of the 
emmers are partially resistant, but the common and club wheats, the 
spelts and part of the emmers are generally classified as susceptible. 
This shows a remarkable parallelism with the sterility groups and sug¬ 
gests the probability that the physical and chemical factor differences 
that cause sterility are also responsible for the differences in resistance. 
It would be expected, if this were the case, that specific sterility factors 
would be linked with resistance, and both would be linked with the 
morphological differences that make up the species. Hayes, Parker, 
and Kurtzweil (15) actually found such linkage, together with the 
expected sterility, in crosses of common with both durum and emmer. 
Linkage was not complete, however, for out of a large number they 
obtained a very few segregates of common type that were resistant to 
stemrust and some of emmer and durum type that were susceptible. 
From this it appears that the physico-chemical factor complex responsible 
for sterility in crosses of so-called immune and susceptible races is not 
identical with those producing resistance, although very closely associated. 
In fact, certain sterility factors may be the identical factors that cause 
certain kinds of resistance, for resistance is specific for each parasite. 
A wheat may be susceptible to stemrust and resistant to yellow rust, 
or resistant to mildew and susceptible to both rusts (2, 9). 
