26 Rorer: Bacterial Disease of the Peach 



the organism isolated from the leaf-spot and the stem-spot is 

 also responsible for this fruit-spot will be pointed out later. 



As to the identity of the organism causing the leaf-spots there 

 does not seem to be much doubt. Soon after the peach leaf-spots 

 were first found, Dr. Erwin Smith suggested to the writer that 

 Bacterium pruni, the organism causing the bacterial black-spot 

 of plums and a plum leaf-spot, was the cause, and though this 

 as yet has not been completely proved, all the work that has 

 been done points to the truth of that suggestion. In the first 

 place the hosts are closely related and have other diseases in 

 common; then too the microscopic and macroscopic appearance 

 of the peach leaf-spots is identical with that of .the bacterial plum 

 leaf-spots. For the past three months the organism isolated 

 originally from peach leaf-spots and Bacterium pruni isolated 

 from plum spots, have been grown side by side in different cul- 

 ture media, such as beef bouillon, nitrate bouillon, Uschinsky and 

 Dunham solution, gelatin, beef agar, milk, litmus milk, and 

 potato cylinders and in all the cultural characteristics are ex- 

 actly the same. Finally, by inoculating with Bacterium pruni, 

 spots may be produced on peach leaves similar in all 

 respects to those resulting from natural infection and from 

 artificial infection with the organism isolated from natural in- 

 fection spots on the peach.* The only thing necessary to com- 

 plete the chain is to produce the plum spots with the organism 

 isolated from the peach leaf-spot. 



Though the twig-spots have not yet been produced by inocula- 

 tion the organism isolated from them has all the cultural char- 

 acteristics of the leaf-spot organism so that it also may be con- 

 sidered to be Bacterium pruni. 



As the fruit-spot was not discovered until the end of the 

 peach season last year but little work has been done on it. 

 Attention is called to it here because of its bacterial nature and 

 its very characteristic appearance. It has not been produced 

 by inoculation nor has the organism been isolated, but the spots 



* In a paper entitled " Occurrence of Bacterium pruni on Peach Leaves," 

 read before the Society of American Bacteriologists at the Baltimore meet- 

 ing, Dr. Erwin F. Smith reported the results of inoculations with Bacterium 

 pruni on peach leaves made in 1 907-1 908, which agree in every respect with 

 those obtained by the writer. 



