A Transmissible mosaic disease oe Chinese 



CABBAGE, MUSTARD, AND TURNIP 



By E. S. ScHUivTz 



Pathologist, Office of Cotton, Truck, and Forage Crop Disease Investigations, Bureati of 

 Plant Industry, United States Department of Agriculture 



In the fall of 19 19, while the writer was selecting different kinds of 

 plants for inoculation experiments with mosaic of Irish potatoes (Sola- 

 num tuberosum Linn.), Dr. W. A. Orton called his attention to mottling 

 in plants of Chinese cabbage (Brassica pekinensis (Lour.) Gagn.), mus- 

 tard {B. japonica Coss.), and turnip {B. rapa, Linn.). The mottling 

 resembled that of mosaic plants of other species, such as potato and 

 tobacco. Diseased and healthy individuals were found in the same plot; 

 the former appeared in groups in some parts of tlie field, suggesting an 

 infectious character of this malady. Evidence bearing upon the nature 

 of this disease, its symptoms, and means of transmission is presented in 



this paper. 



SYMPTOMS 



Mosaic of Chinese cabbage, mustard, and turnip produces a distinct 

 mottling of the leaves, very similar to that of mosaic diseases of the 

 Solanaceae. This mottling is produced by the appearance of irregular 

 light green and dark green areas on the leaves (PI. B ; 22, D, E ; 24, A, B). 

 These light green areas usually adjoin the veins, from which they may 

 extend so as to include a considerable area of the leaf surface between 

 the veins. Another very common macroscopic symptom of this disease 

 is the characteristic ruffling and distorting of the leaf surface (PI. 24, 

 A, B). On the raised areas the dark green patches appear. The leaf 

 margins frequently are much more irregular than in healthy plants, 

 causing some of the leaves to appear somewhat unsymmetrical. In addi- 

 tion to these common abnormalities on the leaves the entire plant may 

 be dwarfed, and the flower stalk and number of blossoms may be con- 

 siderably reduced (PI. 22, B; 23, B). 



OCCURRENCE IN THE FIEED 



Since mosaic individuals appeared among Chinese cabbage, mustard, 

 and turnip plants growing in adjoining plots, interspecific susceptibility 

 was suggested. Furthermore, it was found that a large percentage of 

 the plants were infested with aphids, Myzus persicae Sulz.,^ one of the 



1 Identified by Dr. A. C. Baker, Entomologist, Bureau of Entomology, United States Department of 

 Agriculture. 



Journal of Agricultural Research, Vol. XXII, No. 3 



Washington, D. C. Oct. 15, 1921 



aaa Key No. G-248 



(173) 



