TOBACCO RESISTANT TO BLACK SHANK o 
CAUSE AND SYMPTOMS OF BLACK SHANK 
Black shank is caused by a soil-inhabiting fungus technically 
known as Phytophthora parasitica var. nicotianae Tucker. Under 
favorable conditions the fungus is capable of attacking the tobacco 
plant at any stage of growth. Temperature may determine, to a 
large extent, the rapidity with which it develops. In the seedbed 
the fungus usually attacks the roots of the seedling or the basal por- 
Ficure 1.—Center, row of a susceptible flue-cured variety, showing wilting and 
dying of plants attacked by black shank; right and left, resistant strains 
possessing flue-cured characteristics, obtained by crossing susceptible flue- 
cured varieties with resistant Florida cigar-wrapper variety 301 and backcrossing 
to the flue-cured parent varieties. 
tion of the stalk at or near the surface of the soil. The stems and 
roots of diseased seedlings appear swollen at first and later turn brown, 
and in a very few days the plants fall over. In older plants, the 
fungus usually first attacks the taproot or main laterals and then 
rapidly invades the basal portion of the stalk; the plant may wilt 
and die, however, before any darkening appears on the stem above 
