A BACTERIAL DISEASE OF STONE FRUITS ^ 



F. M. Rolfs 



HOST CONSIDERATIONS 



Cultivated varieties of the apricot (Prunus armeniaca), the nectarine 

 (Prunus persica var. necturina) , the peach (Prunus persica), and the 

 plum (Prunus domestica, Prunus americana, and others), are known to 

 be affected by the bacterial disease discussed herein. It will be noted 

 that the hosts are closely related. 



THE DISEASE 



NAMES 



The disease on the foliage during its early development or in cases cf 

 slight infection is known as bacterial leaf spot; in more advanced stages 

 or in more serious outbreaks it is termed bacterial shot hole. On the fruit 

 it is sometimes referred to as black spot, the growers, however, more com- 

 monly'- speaking of it as bacterial crack. The disease on the young twigs 

 has received the names black spot and black tip, and when open perennial 

 wounds are formed on the branches these are called bacterial cankers. 



HISTORICAL 



The disease is apparently of American origin, it having been found, 

 so far as is known, only in the United States. During the past nine or 

 ten years fruit growers in various sections of the country have called 

 attention to a shot-hole disease of peach and plum foliage, which in wet 

 seasons has in many cases caused premature defoliation. O'Gara (Rorer, 

 1909)^ reports a shot-hole condition of peach foliage prevalent in Georgia, 

 and suggests that it is caused by a bacterial organism. Smith (1903) calls 

 attention to a bacterial disease of Japanese varieties of plum in central 

 Michigan, which appears as a shot hole of the leaves and a black spot 

 of the fruit. Clinton (1904) describes a leaf spot on peach in Connecticut, 

 which he attributes to a bacterial organism. Heald (1906) discusses a 

 disease, apparently of the same nature, found in Nebraska on the twigs 



' Also presented to the Faculty of the Graduate School of Cornell University, June, 1913, as a major 

 thesis in partial fulfillment of the requirements for the degree of doctor of philosophy. 



Author's Acknowledgments. — The writer wishes to acknowledge his indebtedness to Professors Whetzel 

 and Reddiek, of the Department of Plant Pathology, New York State College of Agriculture, for many 

 helpful criticisms and suggestions; and to Director Paul Evans, of the Missouri State Fruit Experiment 

 Station, for his support and cooperation, which made it possible to undertake and complete the work. 



-Dates refer to literature cited, page 435. 



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