June 33,1933 
Inheritance of Resistance to Puccinia graminis 
993 
The most significant feature of Table VII is that six Fg hybrid families 
are shown to have been definitely resistant to both biologic Forms I and 
XXXIV. Considering the reaction of the parental varieties to these 
biolo^c forms, it is very likely that at least one of the two near-resistant 
families was likewise homozygous in its reaction. On this basis it 
would seem that two main differential factors may explain the results 
obtained. These factors, if present, are inherited independently, which 
makes possible the combining of resistance to both forms in a single 
variety. 
Tim REACTION OF THE MINDUM X PENTAD Fg FAMILIES FROM WHITE- 
SEEDED parents to form I AND FORM XXXIV 
Table VIII correlates the results obtained for Fg families from white- 
seeded parents when inoculated with Forms I and XXXIV. Out of a 
total of 34 families 2 were resistant to Form XXXIV and immune from 
Form 1 . The indications of 3: i ratios for Forms I and XXXIV are here 
substantiated in a very close 15:1 ratio. 
TabIvIS VIII .—The classified reaction of the progeny of Mindumy^Pentad white-seeded Fg 
plants to biologic Forms I and XXXIV 
Reaction to Form XXXIV. 
Reaction to Form I. 
Total. 
Immune. 
Near- 
immune. 
Heterozy¬ 
gous. 
Near- 
susceptible. 
Suscepti¬ 
ble. 
Resistant. 
2 
0 
3 
0 
0 
5 
Near-resistant. 
I 
0 
2 
0 
2 
5 
Heterozygous. 
3 
2 
II 
I 
2 
19 
Near-susceptible. 
0 
0 
0 
0 
I 
I 
Susceptible. 
0 
0 
0 
0 
0 
0 
Total. 
6 
2 
16 
I 
5 
30 
The object of giving special treatment to the Fg progeny of white-seeded 
Fg plants is a recognition of the fact that the economic aspects of a prob¬ 
lem warrant careful consideration. Pentad, although high in rust 
resistance, is a poor milling wheat. Owing to the difficulty of distin¬ 
guishing the thrashed grain of one red durum from another, millers have 
come to discriminate against all red dunims. There is consequently no 
immediate future for a new rust-resistant red durum, even though it be 
of good milling quality. 
DISCUSSION 
The study of the reaction of the Fg generation of the durum crosses 
MindumX Pentad and Kubanka No. 8 X Pentad to two biologic forms 
of P. graminis tritici has shown that all combinations of susceptibility 
and resistance to these forms may appear. The reaction of Kubanka 
No. 8 X Pentad Fg families to Form XXXIV indicated the presence of two 
factors with neither susceptibility nor resistance dominant. The re¬ 
sults obtained from Mindum X Pentad Fg families inoculated with 
Form I can be explained on the basis of a single main factor differenc 
with immunity dominant. The data for the reaction of Mindum X Penta 
