320 MAINi; AGRICUIvTURAIv E^XP^RIME^NT STATION. I909. 



In Virginia so far as can be learned from correspondence^ 

 etc., the disease appears to assume more serious proportions 

 wherever it occurs at all, and there seems to be a growing con- 

 viction around Norfolk, and in some places on the Eastern 

 Shore that it comes from and first occurs upon fields planted 

 with northern seed. 



Inoculation into sound tubers with ]3ure cultures of the 

 organisms associated with the disease produces a rapid soft- 

 rot, and no doubt some of the loss from wet rot in the field and 

 in storage is caused by this organism. However, in the writer's 

 experience this is largely confined to the small tubers which 

 have been formed in the hills attacked, before the stalks are 

 killed. Even here only a small part of such tubers are found 

 to be decayed. The disease appears to start from the seed piece, 

 which is invariably decayed, and passes directly up the main 

 stem. The under-ground, tuber-bearing branches of the stem 

 are cut off and the disease follows them out a short distance, 

 but more frequently it stops before reaching the young tubers. 

 If the young tubers are reached a soft, wet decay results. Out 

 of a large number of plants grown in pots and inoculated with 

 pure cultures of the organisms, at or near the surface of the 

 soil, in only a very few cases did the disease spread downward 

 and outward on the underground branches of the stem suffici- 

 ently as to reach and cause decay of the young tubers. 



The fact that the organism so readily and rapidly destroys 

 potato tubers when inoculated into them would indicate that 

 in addition to producing a dangerous stem-disease it has poten- 

 tial qualities for becoming a serious pest as a cause of tub'er 

 decay. However, there is no evidence that this has been the case 

 in Maine in the past. Epidemics of potato-rot are not infrequent, 

 but these are invariably associated with and follow outbreaks 

 of late blight, Phytophthora infestans De Bary, upon the foliage 

 and this fungus is invariably found in the decayed tubers. 

 Even in seasons when the late blight is rife the rot is almost 

 entirely controlled by proper and thorough spraying of the 

 foliage which would not be the case if the blackleg organism 

 was a contributing factor. 



In these epidemics of tuber decay following late blight while 

 the rot as a rule shows the characteristics of that caused by 

 the late blight fungus, there is associated with it very frequently 



