224 



BACTERIA IN RELATION TO PLANT DISEASES. 



Dr. Hunger says: "I succeeded repeatedly in artificial infections with Bacillus solanacearum on 

 sound plants, which then showed the typical phenomenon of the slime-disease. " 



This disease in the tobacco is a specific rotting process caused by Bacillus solanacearum Smith, 

 for the appearance of which a wounding of the plant is first necessary, since the bacteria themselves 

 are not able to enter of their own accord to cause the slime-disease. After a preliminary wounding it 

 is possible for the bacteria to penetrate the plant and to find principally in the vascular bundles their 

 seat of activity. 



The infection takes place chiefly on the underground parts of the plant, although the first notice- 

 able signs of the disease are shown by the wilting of the leaves. 



Whenever the path along which the sap-stream moves is completely stopped up the plant dies in 

 consequence of lack of water. 



The interior of the stem is completely disorganized. In later stages of the slime-disease the rot- 

 ting process is hastened by the appearance of several saprophytic bacteria and yeast species. The 

 tobacco from slime-sick plants is often unripe because, for the most part, it must be harvested too 

 early, otherwise the spots on the leaves form very weak places. 



A great reduction in the spread of this disease would be brought about by avoiding to plant the 

 places where slime-diseased tobacco plants have stood, at least without special precautions. 



It is to be desired that tobacco from slime-diseased plants should be pulled up and not cut, so as 

 to avoid bringing the rotting stems into the shed. The hollow stems filled with slime should be 

 carefully removed and burned. 



In 1909, Jensen published some notes on the Dutch East Indian disease in a general 

 paper on tobacco. Some of his conclusions are as follows : 



Sound and strong tobacco plants are resistant to the slime-disease bacteria. Only when the 

 bacteria are extremely virulent are strong plants made sick and then in many cases these are not 

 killed, but form new sound roots, develop new shoots, and sometimes wholly recover. Serious injuries 

 occur only on fields with less good soil, where the plants in their youth have not been strong enough 

 to resist the bacteria. 



In his first experiment, begun September 30, 1908, on 10 plants, slime was taken directly from 

 the cut stem of a tobacco plant received from Djoganalan and injected into the exposed roots by 

 means of a scalpel and the needle of a Pravaz syringe. After 9 days all the plants became diseased 

 and the lower leaves showed the characteristic dried-out spots. The 10 plants were afterwards pulled 

 up and dissected. The roots were rotted and there were, on cross-section, the characteristic small 

 black spots in the vascular ring. 



I-n the second experiment 70 plants were used. The results were as follows : 



TABLE 22. Jensen's Results. 



None of the inoculated plants died. Most grew well and many reached the height of 

 the uninfected control plants. Neighboring plants were not infected. Following a rain 

 the diseased plants recovered their turgor. Jensen's final conclusion is as follows: 



The slime-sickness, consequently, must be regarded as a true bacterial disease which can develop 

 only under unsatisfactory cultural conditions and which spreads from plant to plant but little or 

 almost not at all. 



In August 1910, Honing published in Dutch a very interesting preliminary paper on 

 the tobacco-disease of Sumatra, which I summarize as follows : 



In all stages of the disease bacteria occur, at first only in the roots, later in the stem and also in 

 the veins of the leaves where they are visible as brown spots on breaking the leaves. 



