expand the scope of possibility for improvement 
in adaptation and productivity of crop varieties. 
Strangely enough, another virus disease, 
curly top of sugarbeet, brought another sugar 
industry to near bankruptcy in the western 
irrigated areas of the United States. Eubanks, 
Carsner, and D, A. Pack produced the first 
partially resistant variety, U.S. No. 1, in 1929 
by mass-selecting resistant plants from com- 
mercial sugarbeet stocks (5). It soon was 
followed by more completely resistant stocks, 
U.S. 33 and 34, selected from U.S. 1. Under 
conditions of curly top exposure, U.S. 34 pro- 
duced over 10 tons, compared with only 2 to 3 
tons per acre by the old commercial brands. 
The breeders of curly top-resistant varieties 
scored a spectacular success that saved the 
sugarbeet crop for large areas in the Western 
United States. 
These contributions to plant disease control 
by resistance breeding are presented to repre- 
sent the multitude of equally significant ac- 
complishments in disease resistance that have 
been built into the structure of modern agri- 
cultural production and have proved their 
stability and value. These successes are time 
tested and solid and can only encourage greater 
research and breeding effort to contain those 
important diseases still resisting control or not 
being vigorously attacked. 
MORE RECENT CONTRIBUTIONS 
TO DISEASE RESISTANCE 
Soybean, a new crop long escaping drastic 
attack by diseases, now suffers from an array 
of important diseases, among them a recently 
destructive root rot disease caused by Phy- 
tophthora megasperma var. sojae. Fortunately 
high resistance was found in relatively good 
types, such as the old variety Mukden, but the 
widely grown and productive varieties were 
highly susceptible. Breeders and pathologists 
of the U.S. Department of Agriculture and 
several soybean-producing States initiated a 
crash program in 1957 to transfer the mono- 
genic resistance of Mukden to the commercial 
varieties by backcrossing. Only 6 years later, 
in 1963, resistant lines essentially isogenic 
with four popular commercial varieties, 
Harosoy, Hawkeye, Lindarin and Clark, were 
119 
cooperatively released in the States concerned, 
followed by a fifth variety in 1964 (22), This I 
believe establishes a record of timely and rapid 
genetic manipulation of a major crop to meet 
a threacening production hazard. 
Open-pollinated corn in the Corn Belt of the 
United States historically has not been beset 
by aerially distributed diseases developing in 
epidemic form. However, severe epidemics of 
the northern corn leaf blight (Helminthosporium 
turcicum) began to occur soon after the estab- 
lishment of susceptible varieties of hybrid corn 
during 1940-50. Early onset of the disease 
2 to 3 weeks after silking may resultin severe 
losses (32), Field resistance to H. turcicum 
has been found, studied genetically, and trans- 
ferred to commercial hybrids that are widely 
available and extensively used (13). This has 
been a difficult and praiseworthy job, with a 
polygenic, hard-to-handle resistance, by co- 
operating State, Federal, and private agencies. 
I have saved until last a discussion of the 
efforts of breeders and pathologists against 
the rust and smut diseases, because the types 
of resistance used have been important in 
limiting the results achieved. However, much 
of the faultfinding with the past pioneering 
efforts is attributable to hindsight and is akin 
to "Monday morning quarterbacking.'' But 
history has been repeating itself so often that 
now there can be little doubt of needed 
redirection of both research and breeding. 
Lest it appear that I see only the hole in the 
rust-resistant doughnut, I wish to reviewafew 
of the many accomplishments that have brought 
immense benefits. 
Stem rust (Puccinia graminis) of small 
grains, has been one of the most elusive 
diseases that breeders have attempted to 
control, but even here the economic gains have 
been tremendous although transient. Craigie 
(7) calculated the gain in yield and income from 
use of stem rust-resistant varieties in Manitoba 
and Saskatchewan, Canada, from 1938, when 
they were first intensively grown, to 1943, The 
calculations were based on extensive and 
dependable yield comparisons of the resistant 
varieties versus the susceptible Marquis. 
Through this 5-year period, the average gain 
was over $27 million annually. This compares 
with an alltime total expenditure on rust re- 
search and plant breeding of less than $2 
million in Canada. 
