A GENETIC AND CYTOLOGICAL STUDY OF CERTAIN 
HYBRIDS OF WHEAT SPECIES 1 
By Karl Sax, Biologist, Maine Agricultural Experiment Station, and E. F. 
Gaines, Cerealist, Washington Agricultural Experiment Statioti 
The cultivated species of wheat can be divided into three definite groups 
based on genetic, taxonomic, and cytological classification. Each of these 
groups has certain specific characteristics not found in the other groups. The 
Einkorn group is of no economic importance. The emmer group is of consider¬ 
able economic importance in certain wheat-growing districts, while the vulgare 
group includes most of the varieties in common use. The emmer group in 
general possesses many desirable characteristics such as disease resistance, 
drought resistance, high protein content, and high yield under certain conditions. 
The vulgare group, on the other hand, is in general susceptible to disease and in 
most cases is not adapted to a semiarid climatic condition, but the only varieties 
of wheat which produce a high quality of grain are in this group. It is only 
natural that for many years plant breeders have attempted to combine the desir¬ 
able characters of the emmer wheats with the high quality of the vulgare wheats. 
It would seem to be a simple problem to combine, for instance, the disease and 
drought resistance of the durum wheat with the high yield and bread-making 
qualities of certain vulgare wheats, but apparently no economic varieties have 
been obtained by combining the desirable characteristics of these two classes 
of wheat species. In the progeny of such crosses certain parental characters 
were found to be associated together, and it was difficult, or perhaps impossible* 
to obtain the desirable combinations in a single individual. 
Crosses of wheat varieties which belong to different groups result in partially 
sterile Fi plants and different degrees of sterility in F 2 . Crosses between different 
species of the two groups result in different degrees of sterility. Some com¬ 
binations show a very high degree of sterility while others are nearly as fertile 
as the parents. 
A study of the chromosome behavior in such partially sterile hybrids has 
shown the reason for the sterility and why certain characters are more or less 
closely associated in the F 2 hybrids. The wheat species in the emmer group 
have 14 haploid chromosomes while those in the vulgare group have 21 haploid 
chromosomes. On crossing species of these two groups with different chromo¬ 
some numbers an Fi plant is obtained with 35 chromosomes in the somatic 
cells. In the reduction division of the Fi there are 14 pairs of chromosomes and 7 
single chromosomes. The 14 pairs of chromosomes undergo reduction in the 
usual manner, but the 7 single chromosomes are apparently distributed at random 
to one pole or the other, so that the gametes will contain from 14 to 21 chromosomes 
(10 ), 2 In most cases, at least, the perfection of the gametes increases as the chromo¬ 
some number approaches 14 or 21, and the gametes with certain intermediate 
numbers are eliminated, due to sterility. Genetic investigations conducted in 
i Received for publication Mar. 31, 1924—issued Nov., 1924. 
1 Reference is made by number (italic) to “Literature cited,” pp. 1031-1032. 
Journal of Agricultural Research, Vol. XXVIII, No. 10 
Washington, D. C. June 7,1924 
Key No. Maine*-17 
(1017) 
