VARIATIONS IN COLLETOTRICHUM GLOEOSPORIOIDES 1 



ByO. F. Burger 2 



Instructor in Plant Pathology, Graduate School of Tropical Agriculture and Citrus 



Experiment Station, University of California 



The diseases of citrus trees and fruit known as wither-tip, leafspot, 

 anthracnose, and tearstain are all caused by the same fungus, Colleto- 

 Irichum gloeosporioides (Penz.) . These diseases have been found in Florida, 

 (4; 5; 9, p. 88), 3 California (j), West Indies, South America, Australia, 

 and Malta; and in practically all citrus-growing regions rather serious 

 outbreaks of some or all of these diseases have occurred from time to 

 time. 



The smaller twigs of citrus trees are very frequently and severely 

 attacked by the fungus. It is quite common to see many of the small 

 twigs killed back 4 or 5 inches. These infected twigs soon turn to a light 

 brown color and sooner or later become dotted over with numerous 

 small black acervuli. After the rainy season begins, the spores, which 

 are imbedded in a gelatinous matrix, exude from the acervuli and are 

 washed down over the fruit and leaves, causing leafspot, tearstain, and 

 anthracnose of the fruit. 



The spores must have an abundance of moisture in order to germinate. 

 Since the rainy season in California occurs during the winter and early 

 spring months, it is at this period that these diseases are most prevalent. 

 In Florida these diseases cause much damage to the citrus industry, 

 whereas in California they are considered of minor importance. This 

 difference in the amount of injury in the two States named is due, I 

 believe, to the difference in the amount of rainfall. During the dry 

 summer in California there is little evidence that Colletotrichum gloeos- 

 porioides is active. In Florida this fungus causes bloom drop and a 

 considerable amount of leaf spotting during the spring and summer 

 months, as well as anthracnose and tearstaining of the lipe fruit. Many 

 growers and agricultural workers believe that the fungus injury is 

 secondary. It has been stated repeatedly that the weak or injured tree 

 is more susceptible to an attack of C. gloeosporioides than the healthy 



tree. 



DESCRIPTION AND HISTORY OF THE FUNGUS 



The fungus, Colletotrichum gloeosporioides (Penz.) was first described 

 by Penzig in 1882 as V ermicidaria gloeosporioides. In 1887 he placed 



1 Paper No. 66, University of California, Graduate School of Tropical Agriculture and Citrus Experi- 

 ment Station, Riverside, Calif. 



2 Resigned June i, 1918. 



3 Reference is made by number (italic) to "Literature cited," p. 735-736. 



Journal of Agricultural Research, Vo1 - :xx > No - 9 



Washington, D. C. Feb. 1. 192 1 



ws Key No. Calif-28 



7 2 3 



