60 



THE DEPARTMENT OF AGRICULTURE. 



NON-PARASITIC DISEASES OF THE TUBEE. 



There are certain troubles not apparently caused by parasites, but rather by 

 physical conditions, such as frost, soil conditions, etc. 



" Hollow-heart " or " hollow-potato" (Fig. 67) is chiefly found in oversized pota- 

 toes and is due to too rapid growth. 



"Internal brown-streak" or "net necrosis" (Fig. 68) much resembles "wilt," 

 but the brown dots are not arranged in so regular a ring, nor confined so much to 

 the stem-end. 



'" Internal brown-spot " appears as larger brown or blackish spots, irregular in 

 shape, scattered through the tuber. 



Both these diseases appear to be due to soil conditions, possibly to overheating 

 of the soil. 



" Black-heart " (Fig. 69), a black rubbery condition of the centre of the tuber, is 

 due to lack of ventilation in storage, especially if accompanied by warmth. 



"Frost-injury" (Fig. 70). Tubers sometimes will become so chilled as to 

 develop internally a fine network of black threads, usually in the outer portions of 

 the flesh. 



Fig. 70. Frost-injury (after Potato Magazine). 



DISEASES OF THE " VINES." 

 LEAF-ROLL (Fig. 71). 



This is one of the newer diseases of potatoes, or perhaps better stated as a 

 disease which has been present for some time in certain parts of Canada, but which 

 only in recent years has begun to attract attention. At present leaf-roll is very 

 little in evidence in this Province; however, the writer found a few plants during 

 the summer 1920. In some parts of Canada, such as in Ontario, leaf-roll was very 

 much in evidence until certified seed was started. 



Leaf-roll was first recognized in Europe in 1905, in the United States in 1911, 

 and in Canada in 1914. 



Symptoms. The plant is considerably dwarfed in size, with foliage slightly 

 discoloured, at times of a lighter green and at others of a yellowish tint. A rolling 

 of the upper leaves may or may not be in evidence ; however, the diagnosis of leaf- 

 roll is most accurately made by an examination of the lower leaves. Here we have 

 an upward rolling of the leaves; one or more leaflets -may be affected. These 

 symptoms are noticeable at an early stage of growth. As the plant matures the 

 tips of rolled leaves turn brown and later on die, and are further characterized by 



