Feb. is, 1921 A Transmissible Mosaic Disease of Lettuce 739 



Six aphids from a colony on mosaic lettuce plants under a cage were 

 transferred on March 15 to each of 16 healthy, rapidly growing lettuce 

 plants under an insect cage. On March 27 several of these plants showed 

 the first symptom of the mosaic disease, as previously described, and 

 there were several aphids on each plant. On this date all aphids were 

 destroyed by drenching the plants with "Black Leaf 40" solution. On 

 March 3 1 there were 4 mosaic and 4 healthy Paris White Cos plants and 

 3 mosaic and 5 healthy Big Boston plants. Sixteen comparable control 

 plants under an adjacent cage were all healthy. On April 15 there 

 were 6 mosaic and 2 healthy Paris White Cos plants and 5 mosaic and 3 

 healthy Big Boston plants. All the 16 control plants were still healthy. 

 Both cages were free from aphids. 



On March 22 three sets of comparable healthy, rapidly growing lettuce 

 plants under three insect cages were treated as follows: Ten aphids 

 obtained from the same colony on mosaic lettuce from which the aphids 

 in the preceding experiment were secured were placed on each plant 

 in cage No. 1. Ten aphids that had presumably never fed on lettuce 

 were collected from a potato field and placed on each plant in cage No. 2. 

 Cage No. 3 was left without aphids, as a control. The first symptom of 

 the mosaic disease was evident on 2 plants in cage No. 1 on March 30 

 (PI. 87, B). On April 14 all 4 Big Boston plants and 3 of the 5 Paris 

 White Cos plants in cage No. 1 showed the mosaic disease, while the 9 

 comparable plants in each of cages No. 2 and 3 were apparently healthy. 

 Aphids were abundant in cages No. 1 and 2 and were lacking in cage No. 3. 



CONCLUSION 



There occurs at Sanford, Fla., a serious infectious disease of lettuce, 

 apparently caused by a parasite not capable of isolation through ordinary 

 microbiological or bacteriological technic. The disease has been trans- 

 mitted experimentally from diseased plants to healthy plants by means 

 of aphids, particularly the species Myzus persicae Sulz. From the symp- 

 toms and general character of the disease, it should undoubtedly be 

 recognized as a true mosaic disease of lettuce. 



