BROWN ROT OF SOLANACEAE. 203 



the foliage of whole fields destroyed in a week, but there is no basis for the assumption that 

 this is the only or the principal cause of the rot of potatoes either in this country or abroad. 

 Species of the fungus form-genus Fusarium also cause, in the United States as well as in 

 Europe, serious diseases of potatoes, one of which begins in the field as a vascular disease 

 of the stems and continues in cellars as a dry rot of the tubers.* The great bulk, how- 

 ever, of the soft rot of potatoes, in this country and also in Europe, is due to bacterial 

 organisms, either acting independently, which is often the case, or following Phytophthora 

 and Fusarium. Several are known to induce decay and very likely a dozen or more dis- 

 tinct kinds of schizomycetes will be found capable of destroying the tubers in wet seasons 

 when the lenticels open in the soil. When this happens all sorts of soil bacteria gain an 

 easy entrance to the tubers under conditions likely to be very favorable to their destruction. 

 This attack of the tubers in a badly aerated, wet soil, with the lenticels wide open, is a very 

 different affair from the active development in the parts above ground, and under normal 

 conditions, which is manifested by Bacterium solanacearum, or by Bacillus phytophthorus, 

 which causes the only other bacterial decay of potatoes which has thus far been described 

 with any great degree of accuracy. Since this was written, Harrison, in Ontario, has 

 described Bacillus solanisaprus, an organism strongly suggestive of Appel's organism but 

 not absolutely identical (see Basal Stem-rot in vol. IV), and Pethybridge and Murphy in 

 Ireland have also described their Bacillus melanogenes, so that in general it may be said 

 that our knowledge of the bacterial diseases of the potato is much further advanced than 

 it was ten years ago, when the rough draft of this chapter was written. 



HISTORY. 



According to Hunger this disease was first recognized by Comes in Italy in 1882. There 

 is much uncertainty, however, concerning this. Professor Comes undoubtedly observed 

 a serious bacterial disease of tomatoes in the vicinity of Naples in 1884 or earlier and recog- 

 nized it as such; but his descriptions of it, and of the fluid cultures made therefrom, do not 

 enable one to speak with any degree of certainty either concerning the signs of the disease 

 or its exact cause. It may have been due to B. phytophthorus or to some other organism. 

 His name, if retained, should apply to a grape bacterium. 



The disease formed brown or black cankers on the stems near the earth, the whole plant 

 being finally destroyed. Bark and pith were disorganized and granular ; the vessels of the 

 wood with their surrounding cells, but not the medullary rays, were occupied by a yellowish 

 or brownish granular mass. "In the disorganized tissues, "says Comes, "and in the gummy 

 granulations was observed the presence of myriads of microbes, similar to those of Bacterium 

 gummis, found by me always in tissues of woody plants affected by gummosis. " 



In 1890, before the Society for the Promotion of Agricultural Science, Prof. T. J. 

 Burrill, of the University of Illinois, described very briefly a disease of potatoes which had 

 attracted his attention as something new, and which was probably this disease. 



The examinations were made on tubers shipped from the south in June, many of which 

 were rotting. Only bacteria were found. Several species of these were isolated, and suc- 

 cessful infections were obtained with the one presumed to be the potential factor in the rot, 

 but these experiments are not described. The organism causing the rot was a termo-like 

 bacterium actively motile, oval to short cylindrical in outline, occurring single, in couples, 

 or rarely in chains of 3 or 4 links, its rods measuring about 0.7 X 1 to 1.5/*; it was non-sporifer- 

 ous, non-liquefying, and formed non-characteristic zoogloeae in the potato. 



How the organisms gain access to the subcortical tissues without some previous puncture of the 

 skin of the tuber has not been ascertained, but some observations seemed to show that the same bac- 

 terium infests the leaves and culms, causing injury and death to these parts and possibly sometimes 

 reaching the tubers through them. 



*See Smith and Swingle, Bull. 55, Bureau of Plant Industry, U. S. Dept. Agric, Feb. 16, 1904. 



