TOBACCO RESISTANT TO BLACK SHANK li 
All later breeding and selection work was conducted in the field on 
soi! heavily contaminated with the black shank parasite. The check 
rows planted with susceptible varieties were usually killed before the 
middle of the growing season. After the original cross, in most cases, 
the plants were self-poliinated and selected for three or more genera- 
tions, or until a fairly uniform line for type and resistance could be 
obtained. In making selections, quality was always considered, since 
resistance without quality would be valueless from a commercial 
standpoint. Plants exhibiting the most desirable flue-cured character- 
istics and at the same time having adequate resistance to black shank 
were selected for future testing. At the time the seed was harvested, 
the seed plants were pulled and the roots and stalks examined to 
determine the extent, if any, of black shank infection. Lines uniform 
for resistance (95 percent or better) and type were obtained after five 
to seven generations of selfing and selecting, but the type was more 
nearly that of the resistant parent, and these lines were not used for 
backcrossing. 
In 1935 a number of the most uniform F; and F, lines showing a 
high degree of resistance were backcrossed to the flue-cured parent. 
In the F, and F; generations following the first backcross it was easy 
to find plants showing a greater number of flue-cured characteristics 
than the resistant parent, but the degree of resistance in these plants 
was generally lower. A few strains with fairly high resistance were 
selected (fig. 1). Physical characters, as shade of flower color, size of 
stalk, angle of leaf fibers, shape of leaf, smoothness of leaf, drooping 
or upright habit of leaf growth, and suckering habit, were valuable aids 
in selecting for flue-cured type. Strains of unusually high resistance 
were developed by crossing first backcross uniform strains of 301 « 
Virginia Bright Leaf with 301 & White Stem Orinoco. 
Second backcrosses to the flue-cured parent were made in 19388. 
The selecting and selfing process was repeated. A few plants having 
very desirable flue-cured characteristics in the F, generation were 
‘again backcrossed to the flue-cured parent. In the following season, 
F,’s from the second backcross and F,’s from the third were planted 
in the field. When the second backcross F;’s produced F, lines fairly 
uniform for type and resistance, they were continued, along with 
_ selections from the related third backerosses. Inbred lines have not 
yet been obtained from the third backcross selections. 
Seven of the most uniform F, lines of the first backcross were 
planted in 1939 in the variety trial tests at the Tobacco Experiment 
Station at Oxford. The results indicated a satisfactory yield, and the 
quality appeared to be fairly good. Chemical analysis indicated that 
from the standpoint of flue-cured tobacco the leaf produced by these 
lines was only of moderately good quality. In field trials made during 
1942, four second backcross lines of the F. generation proved to be 
superior to the first backcross lines tested during 1939. The quality 
compared favorably with that of the better flue-cured varieties. 
Since black-root rot is a disease of considerable importance in the 
flue-cured tobacco areas of the Piedmont, suitable flue-cured varieties 
resistant to both this disease and black shank are highly desirable. 
With a view to obtaining such varieties, 400, which is a root rot 
resistant strain, was crossed with 301 durimg the season of 1935. 
Applying the procedure of selfing and selection, fairly uniform lines 
