The spring wheat Selkirk bred by the Canadian 
Department of Agriculture at Winnipeg, Canada, 
for resistance to race 15B of stem rust was 
released in 1953, and to the presentithas been 
by far the predominant variety in both Canada 
and the spring wheat area of the United States. 
Through this 1l-year period it has maintained 
its resistance in the field in such years as 
1962, when much of the crop was late and 
susceptible varieties, such as Red Bobs, were 
nearly destroyed by stem rust. Financial gains 
thus far from this one variety in Canada and 
the United States probably would extend to 
multiples of $100 million. 
Extreme difficulty has been experienced in 
maintaining oat varieties resistant to crown 
rust (Puccinia coronata avenae) in the entire 
oat-producing area ofthe United States, Never- 
theless, tremendous losses have been pre- 
vented by the breeding of anumber of resistant 
varieties. Accurate measure of gain from 
growing the resistant variety Clintland, from 
Purdue University and the U.S. Department of 
Agriculture, was possible in Indiana in 1957 
during the last severe crown rust epidemic. 
Clintland and other resistant varieties in small 
acreage were grown on 67 percent of the State 
oat acreage. Since Clintland is essentially 
isogenic to Clinton, a susceptible older variety, 
field-plot comparisons over the State gave an 
accurate measure of the relative yields. Gains, 
thus calculated at a value of 62 cents per bushel, 
amounted to about 9.5 million bushels, worth 
nearly $6 million. Here, in a small State, in a 
single year, on one crop, the measured gain 
from resistance to one disease exceeded 
several times the estimated investment for all 
crop-disease research and breeding work in 
Indiana by the State and Federal Governments. 
In 1957, Clintland was probably the most 
widely grown oat in other Corn Belt States, 
where total gains from its resistance were 
many times those measured in Indiana. 
The breeding for resistance to bunt of wheat 
caused by Tilletia spp. inthe Pacific Northwest 
has made possible the maintenance of wheat 
growing in dry areas where bunt spores could 
persist in the soil and seed treatments were 
not effective. A series of resistant varieties 
have been produced first by E. F. Gaines, of 
Washington, who released the well-known Ridit 
in 1924 and Albitin 1927. As required to control 
new races of bunt, these have been followed by 
120 
a series of improved varieties, the most recent 
of which have been Elmar (1949), Omar (1955), 
and Gaines (1962). 
CHANGING RACES 
Satisfaction in this review of victories inthe 
breeding for disease resistance is marred by 
some serious defeats. These defeats have come 
about largely through the development of 
physiologic races of the pathogens causing 
several of the most important diseases of 
our major crops. The depredations of such 
races are too numerous to mention more than 
a few examples. 
Races of stem rust of wheat, oats, and barley 
are probably the most notorious offenders. 
First, race 56 emerged to attack the first 
resistant wheat variety Ceres. Then race 15B 
arose, which could attack the durum wheats 
and the bread wheats Thatcher, Lee, Regent, 
Renown, Apex, and Redman, all having good 
previous records for resistance. The variety 
Selkirk, released in 1953 by the Canadian 
Department of Agriculture, is resistant to 
race 15B. However "biotypes" of races 15B 
and 29 have been found that attack it in the 
seedling stage. It is noteworthy that these new 
"biotypes'' have not become destructive on 
Selkirk through a 10-year period, although they 
must have repeatedly occurred in the vast 
acreage of this variety. 
Stem rust resistance on oats (P. graminisf. 
sp. avenae) has been particularly ephemeral. 
The resistance of Clinton, conditioned by gene 
D, was overcome by destructive epidemics of 
race 7. The resistance of Tama and Vicland 
(gene A) gave way before race 8. Varieties now 
carrying stem- rust-resistance genes A, B, and 
D, those principally used to breed the present 
varieties, are completely susceptible to the 
newer races 6A and 6AF. Thus, we haveno oat 
variety at present that is resistant to all 
well-distributed races. 
The crown rust of oats (P. coronata avenae) 
like stem rust repeatedly has been able to 
vary its virulence sufficiently to thwart the 
best efforts of breeders. Varieties such as 
Clintland possessing the LL gene pair from 
"T.andhafer'' are thoroughly susceptible to 
predominant strains of the rust. At present 
there is no commercial oat variety that is 

