Rorer: Bacterial Disease of the Peach 



25 



periments the conclusion may be drawn that this disease of peach 

 leaves is caused by the yellow bacterium. 



The disease as it occurs on the twigs was first observed by 

 the writer at Siloam Springs, Arkansas, in 1907. It kills the 

 bark of young shoots, forming purplish-black, slightly sunken 

 areas usually Y s to % 6 inch wide which may extend for two 

 or three inches along the stem or even girdle it. At times the 

 whole end of a shoot may be killed. The infections as a rule 

 seem to take place at a leaf scar. The disease was found again 

 last year in an orchard at Bentonville, Arkansas. In each case it 

 was closely associated with the bacterial leaf-spot; in fact many 

 of the diseased twigs had already been defoliated. Sections 

 through the smallest spots showed that bacteria were present in 

 enormous quantities in cavities in the bast tissue, and by the 

 poured-plate method a yellow bacterium was isolated from these 

 spots. The growth of this organism in various media, such as 

 beef, rice and corn-meal agar and on potato cylinders, is similar 

 to that of the organism isolated from the leaf-spots and the two 

 organisms are evidently the same. No attempt has yet been 

 made to produce the disease on the twigs by inoculation. 



The disease as it occurs on the fruit is quite striking and 

 exceedingly characteristic. It was found in two orchards at Ben- 

 tonville during the past season. It causes a very small purplish 

 spot over which the skin soon cracks either in a straight or 

 angular way. The individual spots are scarcely ever much over 

 Y 1Q of an inch in diameter but are usually very numerous (as 

 many as 250 have been counted on one side of a peach), so 

 that the cracks may become continuous and extend for an inch 

 or more. Numerous sections through even the smallest of these 

 spots showed that bacteria were present in enormous quantities 

 and were evidently the cause of the trouble. Attempts to get 

 pure cultures of the organism were not successful because of the 

 cracks and the small size of the spots which made it impossible 

 to sterilize the outside of the peach without killing the parasite, 

 and when plates were poured from spots which had not been 

 sterilized on the outside they became completely overrun with 

 rapidly growing saprophytes. The reasons for assuming that 



