JONATHAN FRUIT-SPOT. 15 



ing experiments. The plat from which the sprayed fruit was taken had 

 received the three usual codling-moth applications, arsenate of lead 

 at the rate of 2 pounds to each 50 gallons of water having been used. 

 Upon arrival an examination of this fruit failed to disclose any of the 

 spot disease in either lot. Both lots were covered over in baskets 

 and left in the laboratory at room temperature and reexamined on 

 September 29. At this time characteristic spots averaging 5 mm. 

 in diameter and from 1 to 25 to each apple were found on 9 per cent 

 of the unsprayed and on 18 per cent of the sprayed fruit. On October 

 23, 65 per cent of the unsprayed fruit was found to be spotted and 

 66 per cent of the sprayed fruit was similarly affected. 



One can only conclude from the results of these experiments that 

 spraying with arsenate of lead is not in any way responsible for the 

 Jonathan fruit-spot. The spots develop on unsprayed fruit as readily 

 as on that which has been thoroughly sprayed with arsenate of lead. 

 It is evident that this poison neither favors nor retards the develop- 

 ment of the disease. 



LABORATORY STUDIES. 



Nearly 400 cultures of the diseased spots have been made in various 

 ways and on various media, but no organism has been isolated with 

 any degree of consistency. A species of Alternaria often occurred 

 in cultures from fruit grown in the eastern part of the country, but 

 cultures from northwestern-grown fruit were almost entirely barren. 

 A few apparently successful inoculations were made by spraying 

 Alternaria spores on Jonathans kept in moist chambers and the 

 fungus reisolated, but both the Jonathan and Esopus (Spitzenberg) 

 are so susceptible to the disease that they are apt to become spotted 

 under any conditions outside of cold storage. In some cases both 

 the inoculated fruit and the controls contracted the disease at about 

 the same time. Spores of this, fungus inserted through needle 

 punctures failed to produce the disease. As Alternaria is very 

 commonly associated with the rotting of apples, especially when the 

 fruit is placed in cellar or basement storage, the possibility of its being 

 the cause of this disease becomes very remote. 



The fungus Cylindrosporium pomi Brooks occurred in a few of the 

 cultures, but this was probably accidental. It is not unlikely that 

 the Brooks spot and the Jonathan fruit-spot occurred together on 

 some of the apples from which cultures were made, and for this 

 reason the fungus causing the former might easily have found its 

 way into a few of the cultures, particularly since the two spots are 

 somewhat similar in appearance. Cultures from the true Brooks 

 spot produced the fungus readily, while those from the Jonathan 

 fruit-spot were, with few exceptions, barren. Moreover, spraying 



[Cir. 112] 



