52 PROTECTION OF PLANTS, 1916-17 



The tubers from affected Evergreen plants showed no evidence of any 

 disease on any part. The yield from such affected vines was not as large as 

 from healthy ojies as the tubers had not completed their growth at the time 

 the vines died. 



Tubers from affected and from healthy E\ergreen vines were placed in 

 separate sacks and saved. These were planted the following year (191.6) 

 and the behavior of the resulting plants observ^ed. The tubers from healthy 

 plants again produced vigorous growing vines which did not become affected 

 with this disease at any time during the year. Tubers from affected vines 

 produced plants that resembled in most respects the plants from Idaho 

 tubers on which the disease was first observed. They were much dwarfed, 

 the petioles and stalks were streaked with brown and were brittle, and the 

 entire plant died early, producing only very small tubers. No healthy 

 plants were observed to contract the disease that year. 



Mr. R. J. Haskell of our department planted a portion of this Idaho 

 seed in 1915 at Hopewell Junction, Dutchess County, N.Y., where he was 

 working on potato diseases at a field station. This same streak disease 

 appeared on several plants from this seed and they behaved otherwise in 

 much the same manner as has been described. 



This disease has been described in some detail here because of i^ts 

 interesting character and because little has been written about it. -It is 

 evidently infectious and of a bacterial nature. Careful work should result 

 in the isolation of the causal organism. Apparently this micro-organism 

 can be carried over winter on the seed, and if this be the only way, disinfec- 

 tion should be an effective remedy. However, unless the disease appears 

 more prevalent than in the past, it is not one requiring preventive measures. 



Returning again to a discussion of the cause of small tubers, it should 

 be pointed out that plants affected with Fusarium and Verticillium wilt, 

 black leg, rhizoctoniose, leaf blights and other diseases, as well as plants 

 lacking vigor, produce small tubers. Since many of these troubles are trans- 

 mitted with the tuber, it can plainly be seen that the continued use of small 

 seed is bound to result in the introduction of diseases of this kind with 

 consequent low production and final running out. The elimination of tubers 

 of such plants from the seed is the practical means of avoiding this 

 condition. 



It should be stated here that tubers which are small because of immatu- 

 rity are not necessarily unfit for seed. Instead, the use of immature seed 

 tubers has been advocated and is practiced by some very successful potato 



