June 23,1923 
Riist Resistance in a Marquis-Koia Cross 
lOII 
(4) The seeds of the F2 bearded plants were o.i mm. longer on an 
average than the seeds from the awnless plants. The seeds of the awn¬ 
less plants had slightly harder texture but were slightly inferior in plump¬ 
ness to those from the bearded plants. Apparently the beard of wheat, 
under the conditions of the experiments, leads to the production of 
somewhat better developed seed. 
(5) Marquis, in the greenhouse, was more resistant than Kota to 
Form XIX. Varying environmental conditions, however, resulted in the 
production of a type of infection on Marquis which approached that 
obtained normally with Kota. The reactions of Kota to Form XIX under 
the same conditions did not show similar variations in the types of 
infection. Fg hybrid families were obtained which reacted in a manner 
similar to Marquis and Kota, while other families were obtained which 
were clearly heterozygous. The results could not be explained on the 
basis of a single genetic factor. 
(6) Kota proved immune from Form XXVII in the greenhouse, while 
Marquis proved resistant. Fg families were obtained which were as 
homozygous for immunity and resistance as Kota and Marquis, respec¬ 
tively, while others were obtained which were entirely homozygous for 
susceptibility. Four types of heterozygous families were obtained. 
Immunity appeared to be dominant to both resistance and suscepti¬ 
bility. The number of seedlings inoculated in each family available for 
the study was too small to m^e the experiment absolutely conclusive. 
The results could be quite satisfactorily explained on the basis of two 
independently inherited factors for immunity and resistance contained 
in the Kota and Marquis parents, respectively, each factor being allelo¬ 
morphic and dominant to a factor for susceptibility. 
(7) Nine biologic forms of stem rust which were collected in the 
North-Central and Northwestern States were used for producing a field 
epidemic. Kota proved rather highly resistant under field conditions 
while Marquis was very susceptible. In one group of 206 Fg families 
there were 28 which were as resistant as Kota. This is a ratio of i to 
7.36. In another test there was a ratio of i resistant Fg family to 8.1 
susceptible and heterozygous. 
(8) The reaction of these Fg families to Forms XIX and XXVII in the 
greenhouse was correlated with the behavior of such Fg families under 
field conditions when an epidemic of stem rust was induced by infection 
with nine biologic forms of stem rust to which Kota proved resistant in 
the field. The study of Fg seedlings in the greenhouse in their reaction 
to Forms XIX and XXVII was not satisfactory as a means of isolating 
Fg lines which would exhibit the Kota type of resistance under field 
conditions. 
(9) The resistance of Marquis to Form XIX and the immunity of 
Kota from Form XXVII were combined in 3 Fg families out of a total of 
372 families studied. This is further evidence in support of the belief 
that there are several genetic factors which determine the differential 
reactions of Marquis and Kota to the biologic forms in question. That 
the resistance of one parent to Form XIX and the immunity of the 
other parent from Form XXVII can be combined in a single hybrid 
family is added reason for the hope that resistance to all biologic forms 
can be obtained eventually. 
