2l6 BACTERIA IN RELATION TO PLANT DISEASES. 



bear almost a normal number of tubers, but are a menace to the crop, as the disease spreads 

 from the small spots on the harvested tubers. 



There can be no injury unless the bacteria come into contact with the vascular bundles. 

 Infection often occurs by abnormal growth of the young stem, resulting in cracks reaching 

 even to the pith. Also through wounds made by animals or otherwise the bacteria 

 easily gain access, e. g., the disease is more prevalent when cut seed-tubers are used. If 

 such are employed they should be covered with moist sacks for two days that the formation 

 of a cork-layer may occur. 



We made agar-poured plates in the laboratory in Washington from the browned 

 vascular bundles of a potato sent from Miinchen, Germany, by Mr. W. A. Orton in 1911, 

 as affected by the bacterial ring-disease, but obtained only a white endospore-bearing 

 motile schizomycete, non-infectious to growing potato stems. 



In Eriksson's book (Die Pilzkrankheiten der Landwirtschaftlichen Kulturpflanzen. 

 Aus der Swedischen uebersetzt von Dr. A. Y. Grevillius, Kempen a. Rh., Reichenbachsche 

 Verlagsbuchhandlung, Leipzig, 1913, pp. 8-9) the ring disease is attributed both in the 

 text and in the figure-description to Bad. solanacearum, 



For further knowledge of this disease we must await Appel's full report. 



THE ENGLISH DISEASE. 



There are a number of statements by English agricultural writers to the effect that 

 Bacterium solanacearum Smith causes a disease of potatoes in Great Britain. These 

 statements, however, are too indefinite to furnish any reliable basis for judgment. 



MALKOFFS DISEASE OF SESAMUM. 



In 1903 a bacterial disease of sesamum was described by Malkoff, from Sadovo in 

 Bulgaria. Early in August 1902, in a plot in which the plants had been watered and had 

 made more rapid growth than in a check plot, many leaves showed brown spots and dried 

 up quickly. Sections revealed the presence of many bacteria. After 2 to 3 days the disease 

 was widespread and the stems were also affected. These were dark brown to black, shrunken 

 and covered with a slimy exudate which dried on the stem. This ooze was at first gray- 

 white, but soon became dark brown. In a few days the stems became entirely black, bent 

 over, and finally dried out. 



Sometimes the whole plant is attacked, sometimes a single shoot (figs. 114 b, c). The disease 

 progresses rapidly and in 3 to 4 days all the leaves are attacked and the stem decayed. It appeared 

 on the early Bulgarian sesamum first, but later occurred on the two Asiatic varieties. The disease 

 was confined to plants which had been in blossom for some time. In the unwatered plot no plants 

 were affected until after a rainfall in September. 



Inoculations of sound leaves and petioles with the juice of the affected plants, both with and 

 without wounds, produced the characteristic signs in 4 to 7 days. In inoculations on plants growing 

 in an unwatered plot, the disease also appeared (in 7 to 24 days) except in case of inoculations on 

 the stem and under side of leaves without wounds. 



Two kinds of bacteria were isolated a short rod and a long one. The first formed yellow col- 

 onies, the second white ones, in 24 to 48 hours at ordinary temperature. Both were motile and 

 non-sporiferous. Growth in bouillon, gelatin, and agar was very luxuriant and the gelatin was soon 

 liquefied. Ten per cent sesamum leaves with peptone and gelatin was an excellent medium. Milk 

 was not curdled by either form, but was peptonized after 8 days by the gray form. Inoculations 

 were made with pure cultures and here and there the disease appeared, but it did not progress rapidly 

 as the tissues were then hard. Those on leaves produced the disease in 7 to 8 days. 



This disease occurred throughout the sesamum-growing district in 1902, but was less 

 widespread that year because of the dry season. In previous years, according to the 

 growers, the entire harvest had often been lost through its ravages. It occurs principally 

 in southern Bulgaria on the Turkish border. The author believes that the disease is dis- 

 tributed on the seed. 



