64 Bacterial Diseases of Plants 



White Rot of Turnips and other Vegetables. 



This disease investigated by Prof. Potter in 1900(30) was the first 

 disease of bacterial origin to be recognised in this country. It is charac- 

 terised by the complete rotting of the tissue attacked, the bacteria 

 secreting an enzyme which has the power of dissolving away the middle 

 lamella from between the cells thus destroying the coherence of the tissue 

 and giving rise to the condition of a "Soft rot." 



Symptoms of the disease. The first symptoms of disease appear in the 

 autumn as a wilting and yellowing of the oldest leaves which droop to 

 the ground, shrivel up and finally rot away. During a fortnight or three 

 weeks the signs of disease progress inwards from the oldest to the 

 youngest leaves until at the end of this period the plant has completely 

 gone to the ground as a rotting, stinking mass. The root is found at this 

 time to be partially or wholly reduced to a greyish white or brown pulpy 

 mass. 



The parasite. Potter was the first to isolate an organism in connection 

 with this disease. He described a small uniflagellate rod under the name 

 Pseudomonas destructans. Johnson and Adams (19) isolated an organism 

 from rotted turnips in the West of Ireland which they believed to be 

 Potter's organism, and also found it to be uniflagellate. They, however, 

 draw attention to the close similarity of this to Bacillus Oleraceae 

 isolated by Harrison (16). Jones (22) obtained a culture of a second 

 isolation from Potter and found the organism to be a bacillus, and Harding 

 and Morse (22) have shown that under similar cultural conditions both 

 Harrison's organism and Potter's second isolation are identical with 

 B. carotovorus Jones. The writer obtained in 1912 a culture of P. de- 

 structans from Krai's laboratory and a slide stained by Loeffier's method 

 showed flagella very indistinctly but each organism appeared to have a 

 single flagellum. In 1916 it was restained bv Steven's modification of 

 Van Ermengen's stain and it was then clearly seen that the majority of 

 the organisms were uniflagellate but that some, perhaps 10 per cent., were 

 bacilli. That the number of flagella in bacteria is somewhat variable has 

 been pointed out by Johnson and Adams (19) and the writer has found 

 that B. atrosepticus grown on living turnips, and also sometimes on 

 living potato, is present mainly in a uniflagellate condition. Potter has 

 agreed (37) that his organism may have been a bacillus. Upon the evi- 

 dence, therefore, it seems well to abolish the name P. destructans until 

 a definitely uniflagellate organism answering exactly to the description 

 given by Potter shall be again obtained from rotted turni])s or other 

 tissue. 



