SPIECKERMANN'S GERMAN POTATO DISEASE. 



In 1910 Spieckermann published brief preliminary articles on two vascular diseases of 

 the potato as found in Germany, the second of which is probably identical with the pre- 

 ceding (p. 161). 



He first considers Appel's ring disease. This is said to be due to bacteria which cause 

 the vascular ring of the potato tubers to become brown, as Appel has pointed out (see 

 The German ring disease, p. 215). These bacteria enter through the underground stem, mul- 

 tiply in the vessels, and in this manner make their way into the tuber. Noticeable changes 

 also take place in the parts above ground. During the course of the summer the shoots 

 become translucent, brownish spotted, and flabby, and the leaves acquire in the veins black- 

 ish gradually enlarging spots, shrivel, and fall off. But the disease may also occur without 

 the spots. 



According to Appel, affected seed tubers produce plants in which the ring-disease is 

 worse than it was the first year. 



Tubers showing Appel's ring disease have been common in Westphalia in recent years. 

 Plates made therefrom gave always pure cultures or mixed cultures of Pseudomonas species, 

 with one polar flagellum or a tuft of such flagella. These cultivated on the ordinary nutrient 

 media showed sometimes fluorescence, sometimes fermentation, and always liquefaction of 

 gelatin. More rarely forms of the mesentericus group were found. Some of these species, 

 when grown on slices of raw potato, caused wet rot like B. phytophthorus . In consideration 

 of the work of Appel further observations were not made. But it should be stated that in 

 Westphalia such infected tubers have often been obtained from plants which above ground 

 show no signs of disease and the stem-vessels of which are free from bacteria; and such tubers 

 when planted out have not given diseased plants. 



Distinct from the above is a vascular potato disease repeatedly observed by Spiecker- 

 mann in Westphalia in the summer of 1908. 



If Appel's ring disease should be designated a Krauselkrankheit, this ought rather, 

 like the basal stem-rot, to be called a Blattrollkrankheit. It is first visible toward the end of 

 July or the beginning of August, through the curving of the leaves upward around the mid- 

 rib. At the same time the otherwise normal looking or only somewhat weakly developed 

 plants slowly turn yellow and gradually wilt. Proportionately to the rapidity of the disease 

 the yield is decreased. 



When examined microscopically the vessels of the diseased stem are found packed full of 

 small, non -motile, rod-shaped bacteria. The same are also found in the vessels of the tubers. 

 But the vascular ring shows at first scarcely any change, at most here and there a minimal 

 yellow stain, which to those not familiar with the phenomena would hardly appear suspicious. 

 But gradually as the vines fall down a striking change occurs. The vascular ring becomes 

 stained a more or less pale yellow; at the same time the ring softens, and this softening 

 extends gradually into the surrounding parenchyma. There occurs consequently a slowly 

 progressive wet-rot in such a way that finally in extreme cases the tuber consists of three 

 distinct parts an external intact bark, a narrow soft zone corresponding to the vascular 

 ring, and a middle intact part, which can be taken out as a whole. 



The progress of this rot is very slow and even in spring numerous tubers can be found in 

 which the softening is limited to single small spots. 



The fate of the tubers depends on how rapidly the disease progresses. The severely 

 attacked tubers die in the course of the winter and become infested with Fusarium. This 

 fungus may also appear earlier. Other tubers look sound in the spring except for darkened 



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