202 MAINE AGRICULTURAL EXPERIMENT STATION. I9II. 



effects Upon the host that so far as the practical agriculturahst 

 alone is concerned the distinctions made are, in the opinion of 

 the writer, of little consecinence. Preventive measures which 

 are effective with one under Maine climatic conditions would 

 be, in all probability, equally applicable to all. Blackleg is not 

 the same as the Southern bacterial disease of the j)otato stem 

 and tuber caused by B. solanacearum Smith. 



Both stems and tubers are attacked. The diseased plants as 

 observed in Maine * first appear more or less unthrifty and 

 usually undersized. The branches and leaves, instead of spread- 

 ing out normally, tend to grow upward, forming a more or less 

 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 pro- 

 gresses rapidly the plants may fall over suddenly and wilt with 

 very little previous signs of disease. The same general symp- 

 toms may be produced by certain other stem diseases, or even 

 mechanical or insect injuries of the stem at or below the sur- 

 face of the ground. 



The appearance of the diseased stems at once differentiates 

 blackleg from other described potato diseases. Stems so at- 

 tacked are characterized by an inky-black discoloration (See 

 Fig. 93) extending from the base of the stem, where it attaches 

 to the seed piece, up sometimes one, two or even three inches 

 above the surface of the ground. Under favorable weather 

 conditions the disease may, in exceptional cases, follow up the 

 stem for several inches, or even out on the larger branches. 

 The seed pieces from which the diseased plants spring are in- 

 variably decayed, and young tubers which have been formed 

 before the destruction of the stem may sometimes be attacked 

 by a soft rot caused b}^ the bacteria being conveyed to them 

 along the underground branches of the stemi upon which they 

 are produced. 



The disease is carried over from year to year by the organ- 

 isms living in decaying, bruised, cracked or otherwise imper- 

 fect seed potatoes. They are readily killed by drying and are 

 probably incapable of existing in a living state on the surfaces 



* The following discussion should be understood as only applying to 

 the character of the disease as observed by the writer in this State. 



