THE JONATHAN FRUIT-SPOT. 1 



By W. M. Scott, Formerly Pathologist, and John W. Roberts, Assistant Pathologist, 



Fruit-Disease Invest igat ions . 



INTRODUCTION. 



In February, 1911, the senior writer 2 published a preliminary 

 report on "A new fruit-spot of apple," 3 in which he stated that the 

 cause of the disease was unknown, but that there was a strong 

 suspicion of injury produced by arsenate of lead used in spraying. 

 It was also stated that the fungi Cylindrosporium pomi Brooks and 

 Alternaria sp. were isolated from a few of the spots, indicating a 

 possible connection of one or both of these organisms with the 

 disease. 



The results of spraying experiments and further laboratory studies 

 conducted by the writers show that the spots are not due to arsenate 

 of lead injury and probably are not caused by any vegetable organism. 



THE NATURE AND IMPORTANCE OF THE DISEASE. 



The spots, though seldom more than skin deep, detract greatly 

 from the appearance of the apple and afford a place of entrance for 

 decay fungi. They are dark brown in color, more or less circular 

 in outline, at first scarcely depressed, later becoming considerably 

 sunken, and vary from one-eighth to three-fourths of an inch in 

 diameter. (Figs. 1 and 2.) They resemble very young bitter-rot 

 spots and are not easily distinguished from the advanced stage of 

 the New Hampsliire fruit-spot (Cylindrosporium pomi Brooks). As 

 many as 25 spots often occur on one apple, and a lenticel usually 

 forms the center of each spot. Since the spots are entirely super- 

 ficial, the intrinsic value of the fruit is not seriously affected, but 

 its market value is greatly reduced. 



The disease occurs only on fully matured fruit and usually develops 

 after the crop is picked. If left on the trees long after maturing, 

 the fruit of susceptible varieties may become affected before being 

 picked. This was observed on the Jonathan variety in Virginia 



1 Issued Feb. 8, 1913. 



^ The work covered by this paper was done previous to the resignation of Mr. Scott, which occurred in 

 February, 1912. 

 3 Phytopathology, vol. 1, no. 1, p. 32-34. 



[Cir. 112] 11 



