THE MONTHLY BULLETIN. 533 



Final Identification of Organism Causing Black Rot. 



Judging by the preceding work, the fulfillment of the rules of proof 

 in the preparation of cultures from affected oranges, inoculations, 

 isolations of the fungus and its constant association of it with the dis- 

 ease, it can be stated with certainty Alternaria citri causes the disease 

 known as "Black Rot of the Navel Orange." 



Discussion of Probable Time and Manner of Natural Infection 



of Oranges. 



Judging by the results of this work with the fungus and also by the 

 ■examination of a large number of affected oranges from the various 

 districts, the following conclusions have been tentatively arrived at, 

 pending further investigations : 



Alternaria citri is primarily a saprophyte and will propagate upon 

 many kinds of vegetable matters, but it is a faculative parasite when 

 ■entrance to the pulp cells of the orange is comparatively easy. The 

 fungus may propagate in the orange groves upon fallen fruit or fruit 

 left on the tree. Thus the spores may be quite prevalent in the spring 

 when the fruit is young and tender. They may be carried by the wind 

 and by insects to the navel or possibly to the blossoms, and, if there is 

 sufficient moisture, develop germ tubes which enter the inner tissues, 

 if there is an opening or imperfection. 



It is not probable that infection takes place in the blossoms but rather 

 after the oranges have grown enough to distend the navel opening. In 

 •every case of infection, except when the peel was split on the outside of 

 the orange, there was found an opening between the convolutions of the 

 tissue of the navel. One orange had two infections and was found to 

 have an opening on each side of the center of the navel. The course of 

 the fungus could be plainly traced from these openings. The fact that 

 seedling varieties are seldom, if ever, affected also indicates that the 

 •extending navel is the place of infestation. 



Discussion of Methods for Preventing Infection of Oranges. 



As stated above, infection without doubt takes place through the 

 navel. If, therefore, it were possible to eliminate the navel from the 

 •orange, infection would be impossible, except in case of a split in the 

 outer peel. But as this would be a slow process, which would require 

 many years, we must look for some other means to prevent infection. 



In some sections spraying with lime and sulphur or Bordeaux Mixture 

 for the withertip disease is practiced in the early spring. If applied at 

 the proper time this may serve to prevent a large percentage of infection 

 by spores of Alternaria citri. 



It is very probable that if a fungicide, such as lime and sulphur or 

 Bordeaux Mixture, was applied well into the navel, just after the latter 

 was distended, infection would be prevented by the destruction of the 

 germ tube of any spore present. Until the time of infection and the 

 manner in which it takes place is exactly determined, remedial meas- 



