A BACTERIAL DISEASE OF LETTUCE 



[ A PRELIMINARY REPORT ] 



By Nellie A. Brown, 

 Assistant Pathologist, Laboratory of Plant Pathology, 

 Bureau of Plant Industry 



In January, 191 5, some diseased lettuce plants {Lactuca sativa) were 

 sent to the United States Department of Agriculture from Nairn, La. 

 The letter accompanying them stated that the disease was ruining the 

 lettuce crop in that section, that about 200 acres of lettuce plants were 

 badly infected, and that the fields looked as though a fire had swept 

 through them. 



At first the growers thought the disease was due to the excessive use 

 of cottonseed meal, but it was reported in fields where no cottonseed 

 meal was used. It occurred on high land, but was most prevalent on 

 flat land. There had been excessive rainfall for three months in the 

 affected region; however, there were fields within 10 feet of the infected 

 area that showed no visible trace of infection. 



The plants received by the Department were full-grown heads with 

 some of the outer leaves entirely shriveled and dried and some of them 

 in a soft-rotted condition. The centers of the heads were sound, but 

 between the center and these dead outer leaves were others affected in 

 varying degrees. In some places there were numerous separated spots 

 with a water-soaked appearance. In other places the spots had fused. 

 Portions of many leaves were in a bad condition, while other parts of 

 the same leaves were sound. 



Razor sections of areas showing the earliest evidence of the disease 

 were examined under the microscope, and numerous bacteria were found 

 in the cells and between them. Fungus threads were not detected. In 

 the advanced stages of the disease the palisade cells and the loose paren- 

 chyma cells had collapsed. Some of the younger diseased areas were 

 used for isolating the organism presumed to cause the trouble, the 

 isolation being made by means of agar-poured plates. The organism so 

 obtained was proved to be infectious. 



Colonies appeared three days after pouring the plates. Those colonies 

 which produced the disease when they were inoculated into healthy let- 

 tuce plants were later studied carefully on agar plates. When very young 

 they are round with entire margins smooth, translucent, cream-white 

 in reflected light, bluish in transmitted light, with fish-scale-like markings 

 which are not always present and which do not seem to be on the surface. 

 These markings disappear as the colonies get older. When 3 days old. 



Journal of Agricultural Research. Vol. IV, No. s 



Dept. of Agriculture, Washingtou, D. C. Aug. i6, 1915 



G— 54 



(475) 



