TOBACCO RESISTANT TO BACTERIAL WILT 



DESCRIPTION OF THE DISEASE 



Bacterial wilt in tobacco is caused by Bacterium solanacearum E. F. 

 Smith, an organism that attacks many other plants also, including 

 tomato, potato, and some common weeds. As it survives in the soil 

 indefinitely, tobacco plants may develop the disease at any time after 

 they are set. The first symptom is usually the wilting of a single 

 leaf, and then several leaves on one side of the plant (fig. 2, A), but under 

 conditions very favor- 

 able for the disease V 

 all leaves may wilt at 

 the same time. To 

 distinguish bacterial 

 wilt from other dis- 

 eases, split the stalk 

 longitudinally. The 

 presence of dark 

 streaks, resembling 

 pencil marks, extend- 

 ing in the woody 

 part of the stem for 

 12 or 18 inches above 

 the soil line is a dis- 

 tinctive symptom of 

 the disease (fig. 2, B). 

 In advanced stages of 

 wilt, a slimy type of 

 soft rot may affect 

 the roots and pith. 



SOURCE OF 

 RESISTANCE 



Tests with all avail- 

 able flue-cured varie- 

 ties showed that 400 

 and Davis Special are 

 slightly less suscep- 

 tible than such varie- 

 ties as Gold Dollar 

 and Virginia Bright 

 Leaf, but this resist- 

 ance did not stand up 

 under severe wilt con- 

 ditions. These re- 

 sults were similar to 

 those obtained by 

 earlier workers who 

 tested varieties of all 

 commercial types of 

 tobacco and found none with adequate resistance. Hence, strains 

 not previously grown in this country seemed the only prospect for iso- 

 lation of highly resistant breeding stocks. 



Figure 2. — Symptoms: A, Young plant, showing 

 (a) the one-sided wilting of green leaves character- 

 istic of the disease early in the season. B, Dis- 

 eased plant, with decayed roots (a) and dark 

 streaks (6) in the wood next to the pith and ex- 

 tending well up the stem. C, Healthy plant. 



