SOME BACTERIAL DISEASES OF LETTUCE 



By Nellie A. Brown 



Assistant Pathologist, Laboratory of Plant Pathology, Bureau of Plant Industry, 

 United States Department of Agriculture 



INTRODUCTION 



This paper is an attempt to classify some common bacterial softrots of 

 lettuce (Lactuca saliva). The rots of lettuce, sometimes very destructive, 

 have needed a critical study for a long time, but they have been rather 

 neglected by plant pathologists, owing partly perhaps to their sporadic 

 character but also partly to the fact that they are difficult to work with, 

 as the soft, slimy character of the rotted tissues is somewhat repellent 

 and also is prompt to invite confusing secondary invasions. Hitherto 

 various softrots have been ascribed to bacteria, but mostly on insufficient 

 evidence, and generally without a proper description of the supposed 

 parasite. This paper deals with four outbreaks of lettuce rot in the 

 United States — viz, (i) The Louisiana disease of 191 5 — already reported 

 in a preliminary way by the writer (Sy ; (2) the Beaufort (South CaroHna) 

 disease of 1916; (3) the Portsmouth (Virginia) disease of 1916; and (4) the 

 Kansas disease of 1^16. It also discriminates two new lettuce parasites 

 (both Schizomycetes) and describes their morphological and physio- 

 logical characters. 



EARLIER LITERATURE 



A short account of the literature on bacterial diseases of lettuce has 

 been given in the paper (8) describing the Louisiana lettuce disease; 

 therefore only an account of a disease of lettuce occurring in the Rio 

 Grande Valley need be referred to. 



Carpenter in 191 6 gave a brief account (9) of an investigation of a 

 lettuce disease occurring in the lower Rio Grande Valley. The general 

 symptoms are those of a gradually dying plant. He describes the gross 

 symptoms as follows: (i) A reddening of the older leaves and blanching 

 of the younger central leaves; (2) a restricted development of newly 

 forming leaves, accompanied by small dark-colored blister spots along 

 the border; (3) the development of numerous lateral adventitious shoots; 

 and (4) dry and dead small roots. Carpenter did not find any parasitic 

 insects or fungi constantly associated with the disease. The symptoms 

 indicated a root trouble, and he believed that the presence of alkali in the 

 soil offered a partial explanation of the disease. 



' Reference is made by number (italic) to " Literature cited," p. 388. 



Journal of Agriculture Research, Vol. XIII, No. 7 



Washington, D. C. May 13. 1918 



nk Key No. G-144 



(367) 



