widespread on open-pollinated and hybrid corn. 
For reasons still not completely understood, 
devastating epidemics were unable to build up 
on most corns, although they appeared to be 
susceptible when inoculated. However, the 
fact that the environment is often favorable to 
this rust is evidenced by severe infections that 
have been observed on sweet corn and certain 
dent corn inbreds with high susceptibility. 
Apparently, as proposed by van der Plank (34), 
corn possesses a generalized and stable re- 
sistance to leaf rust. This ''generalized"' and 
permanent type of resistance of corn draws the 
jealous attention of those of us who have fought 
the battle against rust races of the small 
grains with some wins and some losses. We 
shall return to consider the possibilities in 
such resistance that may provide the clue to 
building better resistance to many important 
diseases. 
Another disease resistance that has been 
around for a long time and has served well is 
field resistance in the potato to the late blight 
disease caused by Phytophthora infestans. 
Breeding for blight resistance began over 100 
years ago in Europe after the devastating 
epidemics of the 1840's and the Irish potato 
famine of 1845 (2). Good varieties were de- 
veloped by 1900 with moderate resistance, 
enough to greatly reduce losses and to render 
control by fungicides more effective. Such 
resistance has formed the basis for modern 
breeding for polygenic field resistance, which 
has remained stable through the years, although 
not of a high or immune type. 
Possibly the most sensational work on dis- 
ease resistance of all time is that of the 
pioneer workers against the wilt diseases 
caused by forms of the fungus Fusarium 
oxysporum. These diseases were devastating 
on a wide array of major crops, ranging from 
flax to banana. Because the causal fungi reside 
and persist in the soil, they are able to attack 
persistently and with increasing severity after 
the soil becomes infested. 
W. A. Orton of the U.S, Department of Agri- 
culture conceived the idea of selecting indi- 
vidual plants that survived on wilt-infested 
soil, although the cause of the disease was not 
then known nor were the principles of pure 
line selection or Mendelian inheritance. By 
1899, he had selected wilt-resistant lines of 
cotton from infested fields in South Carolina 
118 
and within 10 years had released a group of 
named varieties (6). 
The flax crop of the United States made its 
"last stand" in the middle Northwestern States 
in the first decade of the century. It continu- 
ously had been forced to move westward from 
the Atlantic States to avoid 'flax-sick"' soils, 
where the crop had been grown for afew years 
(8). The crop was saved by the pure line- 
resistant selections of H. L. Bolley of North 
Dakota made during 1902-12 and distributed 
from 1908 to 1925. 
I witnessed the end of the struggle to grow 
wilt-susceptible flax in eastern South Dakota 
about 1910. I recall a large fieldon my uncle's 
farm, where the flax crop had made normal 
growth and was in full flower. But on this day 
every stalk was flaccid and the flowers hung 
limp. This was about the end of flax growing 
in that region until Bolley's resistant selections 
brought it back some years later. Wilt re- 
sistance became a must for crops that were 
attacked by the fusarium wilt fungus. Today the 
cabbage-, pea-, tomato-, and melon-growing 
industries in many areas owe their existence 
to the development of fusarium wilt-resistant 
varieties. 
Sugarcane mosaic, known in Asia in the past 
century, is believed to have been introduced 
into the Southern United States about 1914. The 
disease spread rapidly and by 1926 had brought 
the industry to near ruin. Production in 
Louisiana of over 200,000 tons had been re- 
duced to 47,000. Losses to the industry 
amounted to $100 million annually (8). 
A breeding project was established at Canal 
Point, Fla., by the U.S. Department of Agricul- 
ture, under the leadership of E, W, Brandes, 
to find or breed mosaic-resistant replacements 
for the old varieties D74 and Louisiana Purple. 
Resistance derived from the wild sugarcane 
Saccharum spontaneum was combined in re- 
sistant improved types by crosses with com-= 
mercial varieties of Ss. officinarum (6). Within 
10 years, following the collapse of sugarcane 
production in 1926, planters and sugar fac- 
tories were back in business with resistant 
varieties that were far better adapted and more 
productive than previous varieties ever had 
been (3). This was an early and impressive 
demonstration that crossing of genetically 
diverse parents, as enforced by breeding for 
disease resistance in this instance, may greatly 

