BLACK ROT OF THE NAVEL ORANGE/ 



(Alteniaria citri. Pierce aucl Ellis.) 

 By Edw. O. Amundsen. 



Introduction. 



Each year since the early nineties a percentage of the navel orange 

 crop of the State of California has been affected by a black rot dis- 

 ease of the pulp cells, generally starting at the navel and extending 

 more or less deeply into the tissues towards the heart of the fruit. 

 This disease is known by all of the following names: "Black Rot of 

 the Navel Orange," "Navel Rot of the Orange," and "Black Heart." 



As it is a disease of the navel varieties almost exclusively, and was 

 first described by Pierce under the name "Black Rot of the Navel 

 Orange," that name has been used in this work. 



This disease is so common that almost every person has been 

 obliged at some time to cut away a larger or smaller part of an 

 orange affected by it. This loss to the consumer represents a part 

 of the total loss due to the ravages of the fungus and is, of course, 

 impossible to estimate. Many oranges, in which the disease has devel- 

 oped considerably, fall from the tree early in the season. Others, 

 infected later or in which there has been little development of the 

 fungus, hang on the tree and on account of the very high color are 

 readily seen and are prized for early eating. They mature earlier 

 than the rest of the crop. 



Compared with other diseases of the citrus fruits and trees, this is 

 not of much economic importance. However, as the total value of 

 an average crop of navel oranges of the state is enormous, even a 

 very small percentage of that value represents a considerable sum. 

 Also there is a possibility that the percentage of infection may run 

 quite high if conditions favor the dissemination and propagation of 

 the disease producing spores. 



Previous Accounts of the Disease. 



The first known account of this disease was written by Newton B. 

 Pierce and appeared in the Botanical Gazette, 1902, pages 234-235, as 

 follows : 



"A fungous disease of the navel orange has attracted attention in the 

 orange-growing districts of California for the past eight or ten years, 

 and was named Black Rot by the writer on account of the color of the 



'This original article was written by the author as a thesis for tire degree of Bache- 

 lor of Science in the University of California. This presentation contains those por- 

 tions of the thesis which we believe will be of most interest to the citrus g'rowers 

 of the State. Practically all the work was done under the direction of Prof. W. T. 

 Home, in the pathological laboratory at Berkeley, California. A little observation in 

 the field was carried on in connection, but no experiments in infection work to date. 

 It is proposed to carry on artificial inoculation experiments during tire season of 

 1913, beginning with the blossoms and continuing until the fruit is full grown. Thus 

 it is hoped the time and manner of natural infection will be ascertained and the study 

 completed. 



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