Mayi3, igis Some Bactevial Diseases of Lettuce 373 



Specimens of a lettuce disease which occurred in Hutchinson, Kans., 

 were also sent to the writer by Mr. Melchers. This disease affected the 

 Grand Rapids (loose-leaf) lettuce, the only variety at Manhattan not 

 affected with the marginal disease. These plants had tiny irregular 

 spots all over the blade and in the midrib; they were yellowish red in 

 color, almost like rust spots (PI. 34). In some places the spots coalesced. 

 As in the Manhattan disease, bacteria were found swarming in the dis- 

 eased places when cross-sections of those areas were examined micro- 

 scopically. An organism was isolated from the Hutchinson plants which 

 proved to be identical with the Manhattan organism. Inoculations 

 proved this organism to be infectious. Besides the yellowish-red speck- 

 ling, marginal infection also occurred. Successful inoculations were 

 made into the Boston Head and Golden Queen varieties. 



No further spread of the disease in this Hutchinson greenhouse was 

 reported. The infection in all probability arose through an accident to 

 the subirrigation system, for it was learned that in watering the plants 

 through one of the tiles, the hose in some way worked out and threw 

 the water for about half an hour over that part of the greenhouse where 

 the disease occurred later. Because the disease did not occur on other, 

 more susceptible varieties, and because the water from the disrupted 

 irrigation system did not deluge those varieties, the accident is quite 

 significant 



It is the writer's opinion that the organisms dried up on the leaves of 

 the Grand Rapids lettuce at Manhattan before they had a chance to 

 enter them ; consequently that variety did not become infected at the same 

 time as the others in the same house. The very nature of loose-leaf 

 varieties is such that there is better ventilation between the leaves; and 

 if the young rosette at the center dries quickly after watering, there is 

 little chance for the bacteria to get inside the leaf, since laboratory tests 

 of this organism have shown that it is killed very readily by drying. In 

 the case at Hutchinson where the disease occurred on the Grand Rapids 

 variety, there was little chance for the drying out of any part of a leaf 

 outside or toward the center of the head while the irrigation system was 

 out of order. It is likely the bacteria were washed from the soil into the 

 breathing pores of the leaves, for their presence later in irregular spots 

 all through the blades shows that they took advantage of this condi- 

 tion, which was not confined to the margins of the moist center leaves. 



ISOLATIONS AND INOCULATIONS WITH ORGANISM FROM THE SOUTH 



CAROLINA LETTUCE 



The organism was isolated from the interior of the stem of the diseased 

 South Carolina plants which showed the brown discoloration and also 

 from the young spots on the leaves. The leaf portions were sterilized 

 for one minute and the stems for two minutes in mercuric chlorid 

 (i : 1,000), washed in sterile water, mashed up in bouillon, and agar 



