PIvANT DISEASES 



DISEASES NOT DUE TO PARASITES 

 OR OF UNKNOWN ORIGIN. 



1 124 - Investigations on the Formation of Cracks in Potato Tubers. — zimmermann, 



H., in Zeit-ichrift fiir P/laiizenkrankheitcn, Vol. 26, Fasc. 5, pp. 280-285, Stuttgart, July 

 30, 1916. 



In this paper the author gives an account of the investigations carried 

 out during the 3'ears 1906-1915 b}' the section of plant diseases at the Ros- 

 tock Agricultural Experimental Station, concerning the formation of in- 

 ternal cracks in potato tubers. The results of these very detailed experi- 

 ments can be summarised as follows : 



The cracks are formed in places where the fields have received too much 

 nitrogenous manure. Owing to the low degree of starch formation the mid- 

 dle tissue of the tuber is poor in starch and transparent in sections. This 

 central tissue is naturally not rich in starch, and the formation of cracks 

 in this region is probably correlated with the lack of starch and is caused 

 by the characteristic growth which is encouraged in the tubers by too 

 exclusive a treatment with nitrogenous manure. The cracks nearly always 

 begin in the middle of the tuber ; when they extend to the outside, the po- 

 tato is rotten inside owing to the inroads of bacteria. 



Often the middle of the tuber is discoloured and lumps of tissue are 

 found instead of the cracks. vSometimes also the darkening of the central 

 region is replaced by a brown zone extending inwards from the point of 

 attachment of the stalk and stretching along the vessels, a feature which 

 is also seen in the potato disease known as " Ringkrankheit ". 



The manures that chiefly encourage the appearance of these phenomena 

 are : Chili saltpetre, farmyard manure, and serradilla used as a green ma- 

 nure. It is stated that up to the present time the disease has onh^ appeared 

 in light soils. 



According to the author the disease is by origin related to the " Eisen- 

 (Bunt-) fleckigkeit " and the " Kringerigheit " of tubers. It would be ne- 

 cessary- to experiment further before deciding whether metereological con- 

 ditions play the same part. 



