372 Journal of Agricultural Research voi. xiii. no? 



THE KANSAS LETTUCE DISEASE 



Another lettuce disease which has proved to be of bacterial origin came 

 to the writer's attention through Mr. L,. B. Melchers, of the Kansas 

 Experiment Station. This was a disease of greenhouse lettuce (PL 33, 

 A, B), and from the material submitted a bacterium not previously 

 reported to be infectious to lettuce was obtained. Mr. Melchers's data 

 on varietal susceptibility, appearance of the disease, etc., which were 

 made in the greenhouse at Manhattan, Kans., are as follows: 



The day temperatures in the greenhouse where the lettuce varieties were grown 

 ranged as closely to 70° F. as possible, while the night temperatures ranged between 

 50 and 56° F. The disease first appeared about December 27, igi6, when most of 

 the varieties were about half grown. The plantings had been made from October 19 

 to 26. Black Seeded Simpson (leaf lettuce) was the first to show the disease and this 

 variety became badly affected. A second planting proved just as susceptible. The 

 leaves in rosettes that are about half grown are perhaps the most susceptible. The 

 Improved Hansen (head lettuce) also became badly attacked; it was second in 

 susceptibility to Black Seeded Simpson. Big Boston (head lettuce) was about as 

 susceptible as Improved Hansen. Early Curled Simpson (leaf lettuce) was less sus- 

 ceptible than the three mentioned varieties. Vaughan's All Season (head lettuce) 

 only showed slight infection. Grand Rapids (leaf lettuce) seemed immune to attack, 

 the disease did not appear on this variety. 



The symptoms of this disease are quite striking. At first a slight marginal wilting 

 takes place in more or less localized areas on leaves about the same age in the same 

 whorl. The areas attacked in the leaf margins may vary from mere specks to areas 

 two or three centimeters long and by coalescing, areas extending seven centimeters 

 have been observed. The diseased areas scarcely ever extend more than three centi- 

 meters down the leaf, generally less than this. On the older leaves the most common 

 sign is the wilting of the tips. The areas affected lop over and gradually become dry. 

 The vascular tissues at this stage frequently show a distinct browning. In a few days 

 the affected areas turn brown, tan, reddish, and sometimes black; the tissues become 

 papery and dry in texture. This disease does not progress down the entire leaf, but 

 ceases development after it extends a short way. It does not cause a rot or soft decay 

 of lettuce but mars its appearance, so that it is not salable. Frequently the wilting 

 symptoms do not appear until after a discoloration of the vascular system is noticed. 

 Often brownish, water-soaked areas are seen and these tissues are turgid at the time. 

 A speckled appearance is sometimes observed below the margins. This is caused by a 

 slight discoloration of the vascular system in localized regions. 



In a letter Mr. Melchers stated that he felt satisfied the infection comes 

 from the soil and is carried to the plants by watering and by currents 

 of air, that he suspected the disease was of bacterial origin, and that 

 the organism gets its start by entering the younger leaves at the tips, 

 where moisture is likely to remain for a longer time. 



Spraying inoculations made with the organism isolated by the writer 

 from the Manhattan plants proved that the organism enters the young 

 leaves at the tips if they are kept moist. No wounding of the plants is 

 necessary; poor ventilation is the only requisite after the plants are 

 sprayed with water suspensions of young agar cultures. 



