CHAPTER IV. 

 ROTS. 



BLACK ROTS OF CABBAGE. 



Pseudomonas campestris Pammel (Erw. Smith). 



This disease is widely distributed in the United States and Europe, 

 and has become so serious on many truck farms that gardeners dread 

 its appearance as much as orchardists do pear blight. It is not confined 

 to cabbage, but it attacks other cruciferous plants such as cauliflower, 

 kohlrabi, kale, rape, turnips, mangels, rutabagas and mustards. 



SYMPTOMS. The first symptom is the withered, yellow margin of 

 the leaf, giving the impression of a" burned edge." The progress of 

 the disease is inward and downward through the vascular system, as 

 is indicated by the brown or black color of the veins and midrib. The 

 tissue of the vascular bundles is destroyed and the cell walls of the 

 adjacent tissue are dissolved, presumably by a cytolytic enzyme.* In 

 this way practically all of the tissues are softened, disorganized, and a 

 general infection of the whole plant may follow. Diseased leaves fall 

 prematurely, leaving a long naked stalk with a tuft of leaves at the top. 

 The dwarfed, one-sided growth of the heads, and in some cases the 

 failure to produce heads is characteristic. 



METHOD OF INFECTION. Water poref infection along the margin of 

 the leaf is believed to be the most common method of entrance, although 

 root inoculation at the time of transplanting undoubtedly takes place also. 

 It has been shown, further, that the germ is introduced on the seed.f 



CAUSAL ORGANISMS. Pseudomonas campestris Pammel, is a short rod with 

 rounded ends, relatively shorter in the host tissue than on culture media, 0.7/1 to 3.0/1 

 by 0.4/1 to o-5/t; motile when young by one polar flagellum; no capsule demonstrated, 



* Smith, Bui. 25, Bur. Plant Industry, U. S. Dept. Agr., 1903. 



f Russell, Bui. 65, Wisconsin Exp. Station, 1808. Smith, Farmers' Bui. 63, U. S. Dcpt. 

 Agriculture. 1898. 



| Harding, Bui. 251, N. Y. Experiment Station, 1904. 



For a means of distinguishing Ps. campestris, Ps. phaseoli, Ps. hyacinthi and Ps. stewarti, 

 the student is referred to Bui. 28, p. 149, Div. Veg. Phys. and Path., U. S. Dept. Agr., 1901. 



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