RUST RESISTANCE IN WINTER-WHEAT VARIETIES. 3 
mercial value of the durums. Carleton (8), in discussing the stem- 
rust epidemic on wheat in 1904, observed that no wheat varieties, 
with the exception of einkorn and some of the durums, spelts, and 
emmers, showed marked resistance under all conditions. He stated 
further, that during ordinary seasons when stem rust may be quite 
prevalent the hard-kerneled Russian winter wheats are considerably 
more resistant to rust than other varieties ordinarily grown. 
Bolley (4, 5), Biffen (2), and Nilsson-Ehle (33) were among the 
first to conduct wheat-breeding experiments with the definite object 
of obtaining rust-resistant varieties. No definite plan or method of 
study, however, was described until Johnson (20) explained the 
methods used for producing an artificial rust epidemic in Minnesota 
and furnished a working basis for the studies which have been made 
since in this country in breeding cereals for rust resistance. These 
methods are further described by Freeman and Johnson (12). They 
state that certain varieties, such as Extra Squarehead in Sweden, 
American Club in England, and Rerrarf and Ward’s Prolific in Aus- 
tralia, have been shown to be resistant to rust. They add, however, 
that some of these varieties can not be said to be universally rust 
resistant, as their behavior in different countries to different biologie 
forms of rust is variable. 
Field experiments have verified early observations that some of the 
durums and emmers are much more resistant than the common 
spring-wheat varieties. Stakman (37) found this to be true in both 
field and greenhouse experiments. Melchers and Parker (29, 31) 
recently have called attention to the resistance of three winter-wheat 
varieties to stem rust and leaf rust. Waldron and Clark (42) have 
described a variety of common wheat named Kota and stated that 
it was resistant to the strain or strains of stem rust prevalent at 
Fargo, N. Dak., Brookings, S. Dak., and St. Paul, Minn., in 1918. 
These authors state that ‘this resistance is decidedly greater than 
that possessed by the common spring wheats and second only to the 
more resistant durum wheats.’’ Clark, Martin, and Smith (10) 
speak of the rust behavior of varieties of durum and common wheat 
grown during the seasons of 1914 to 1919 at several field stations in 
the northern Great Plains. They state that none of the varieties of 
common wheat grown is really rust resistant, but early-maturing 
varieties have ripened before the rust has developed extensively and 
are sometimes rust escaping. Most varieties of durum wheats are 
more or less rust resistant, as compared with common wheats. Acme, 
Monad, and D-5 are known to be especially rust resistant. In years 
of heavy rust infection these varieties have produced the highest 
yields. When grown under comparable conditions in these and 
other experiments, the D—-5 variety shows the greatest resistance of 
all varieties to stem rust. 
