ANGULAR LEAF-SPOT OF CUCUMBERS 



By Erwin F. Smith, Pathologist in Charge, and Mary Katherine Bryan, Scientific 

 Assistant, Laboratory of Plant Pathology, Bureau of Plant Industry 



INTRODUCTION 



The angular leaf-spot of cucumbers {Ciicumis satimts) has been known 

 in the field for many years, but up to the present time no organism has 

 been named as its cause, though it has been generally conceded to be of 

 bacterial origin. The disease is characterized by the formation of 

 numerous, often confluent, angular, dry, brown spots which by drop- 

 ping out or tearing give the leaves a ragged appearance. 



The literature on the subject, aside from mere notes on the occurrence 

 of the disease scattered through pathological literature, consists of four 

 papers by O. F. Burger, of Florida,^ and a more recent Italian paper by 

 Traverso.^ Burger mentions the leaf-spot as preliminary to a more 

 destructive fruit-rot, said to be due to the same organism. His descrip- 

 tion of the diseased leaves agrees with the appearance of leaves sent to 

 the writers from Wisconsin, as well as with those obtained by them 

 from other yStates, and with the leaf -spots which they obtained in Wash- 

 ington by pure-culture inoculations. A brief description of the causal 

 organism is given in each of his papers, in one case with the group 

 number according to the chart of the Society of American Bacteriologists. 

 Burger's descriptions agree in the main except as to flagella and the 

 diameter of his organism. In his earlier descriptions it is said to have 

 polar flagella, but in the later ones it is reported to be peritrichiate. 

 No name is given to the bacillus. 



Traverse's paper is only a preliminary one, but it leaves no doubt as 

 to the identity of the Italian and American disease. A motile, fluor- 

 escent, nonliquefying organism was isolated by him and inoculations 

 were made with it, but no positive results were obtained (p. 459). 



Who first reported this cucumber disease in the United States is 

 uncertain; the senior writer has known it for 20 years, and several years 

 ago (1904) plated out two yellow bacteria with which unsuccessful 

 inoculations were made. Again, in 1907, at his suggestion, Mr. John R, 

 Johnston, then of the Laboratory of Plant Pathology, made platings 



1 Burger, O. F. A new cucumber disease. In Fla. Agr. Exp. Sta. Rpt. [i9ii]/i2, p. o-ci. 1913. 

 A bacterial rot of cucumbers. In Phytopathology, v. 3, no. 3, p. 169-170. 1913. 



Bacterial rot of cucumbers. In Fla. Agr. Exp. Sta. Rpt. [i9i2]/i3, p. xc-xciv, fig. 11-13. 1914. 



Cucumber rot. Fla. Agr. Exp. Sta. Bui. 121, p. 97-109, fig. 37-42. 1914. 



2 Traverse, G. B. Sulla bacteriosi del cetriolo in Italia. Nota preliminare. Atti R. Accad, Lincei, 

 Rend. 01. Sci. Fis., Mat. e Nat., s. 5, v. 24, sem. i, fasc. s. P- 456-460. Apr. 5, 1915. 



Journal of Agricultural Research, Vol. V, No. 11 



Dept. of Agriculture, Washington, D. C. Dec. 13, 1915 



bl G— 68 



■ (465) 



12571°— 15 2 



