312 maixe: agricultural lxperime^nt station. 1909. 



over preliminary work upon fermentation with an authentic 

 culture of B. solanisaprus in comparison with the organisms 

 isolated in Maine suggest the possibility that the differences in 

 fermentative ability are not so great as was first supposed. 



The blackleg organisms differ in cultural characters and in 

 their effects upon the host from Bacillus solanacearum Smith, 

 the cause of the Southern bacterial disease of the potato and 

 egg-plant. 



Character and x'Vppearance; of thi; Disease. 



Plants aft'ected by blackleg are readily distinguished in the 

 field by any close observer, even at a distance. However, at first 

 sight the general aspect of the diseased plants does not differ 

 materially from that produced from several other causes which 

 injure or kill the parts below or at the surface of the ground, 

 such as theFitsarmm disease, the Rhizoctonia trouble, or even 

 mechanical injury to the stem. The affected plants appear more 

 or less unthrifty and usually under sized, varying with the 

 severity of the attack. The branches and leaves, instead of 

 spreading out normally, tend to grow upward, forming a some- 

 what more compact top, frequently with the young leaves curled 

 and folded up along the mid-rib. Later they become lighter 

 green or even yellow and the whole plant gradually dies. If 

 the disease progresses rapidly, the stem may fall over quite sud- 

 denly and wilt with very little previous signs of disease, other 

 than the upward tend of the foliage noted above. 



The diagnosis of suspected cases is easily confirmed by pull- 

 ing up the affected plants. Blackleg as its name indicates, is 

 characterized by a pronounced blackening of the stem below 

 ground, usually running up one, two, or even three inches above 

 the surface. Sometimes under very favorable conditions, i. e. 

 continued wet, cloudy weather, especially where plants are grow- 

 ing on a naturally moist soil, the inky-black discoloration may 

 follow up a portion of the stem for several inches above the 

 ground.* During the active progress of the disease the invaded 



* Inoculation of leaf petioles, or any part of a potato stem above or 

 below ground with cultures of the bacteria isolated from diseased stems 

 invariably produced the same characteristic black lesions. One plant 

 was found in the field, however, which was affected with a rapid soft 



