EXPERIMENT STATION BULLETINS. 667 



SUMMARY. 



This bulletin gives the results of experiments with the Leaf-Spot dis- 

 ease of tomato and recommendations for its control. After a discus- 

 sion of the previous work on the disease, the disease is discussed under 

 topics: — Name, Economic Importance, and Distribution. The disease 

 manifests itself by forming lesions on leaves, stems, calyx, and fniit. 



Since previous work for the most part inferred the connection of the 

 associated fungus and the disease, or at least was not entirely conclu- 

 sive, formal proof of parasitism was undertaken. This work proved that 

 the organism, Septoria lycopersici Speg., causes the disease. Studies of 

 infection phenomena were given under the topics: — Period of Incuba- 

 tion, Subsequent Development, and The Relation of Infection to Mois- 

 ture. 



The physiological and ecological relations of the causal organism were 

 studied under the topics: — Germination, Growth on Media, Relation to 

 Dessication, Heat, Light, Oxygen, and Dissemination. 



Morphology of the causal organism indicated that the pycnidium is 

 a closed ball with a wall similar to that in the genus Phoma. The spores 

 are long and needle-shaped bodies with pointed or rounded ends, usually 

 with several septa. The mycelium is of two sorts. The morphology of 

 this organism shows a striking difference from that found in the mem- 

 bers of the genus Septoria studied by Potebnia, Diedicke and Klebahn. 

 There is no proof available to show that the organism in the United 

 States is different from that in Argentine, hence the specific name, lycop- 

 ersici, is retained. 



In considering the relation of the fungus to the host, it was found that 

 the type of infection is stomatal. The mycelium is intercellular and 

 possesses haustoria. 



An experiment to determine the morbid physiology of the plants in- 

 fected by Septoria indicated that healthy and diseased plants transpired 

 nearly alike per unit of area. There was, however, an indication that 

 the diseased spots transpire more than the healthy portions of the af- 

 fected leaves, and that the transpiration of these healthy portions is 

 repressed below normal. The fungus was found to infect the potato when 

 the latter is artificially inoculated. No fruiting bodies were produced in 

 the disease spots. No variety of tomato was found especially suscepti- 

 ble or immune although more than fifty were tried. Control measures, 

 chiefly prophylactic, are recommended. 



