CLITOCYBE ROOT ROT OF WOODY PLANTS 23 



The root rot produced by this fungus is so similar in general aspects 

 to that produced by the closely related root rot fungus ArmAllaria 

 mellea, that in the absence of fruiting bodies or cultural studies, the 

 diseases caused by these respective fungi may be confused readily. 

 A. mellea occurs in all States where G. tabescens occurs, but in Florida 

 G. tabescens is by far the more prevalent fungus. 



Clitocybe root rot attacks not only native forest trees but also 

 plantings of tung trees and a wide variety of fruit and ornamental 

 trees, shrubs, and vines, including many exotic ones. In Florida, the 

 only State in which this disease has been studied intensively, it has 

 been recorded as attacking 210 species of plants belonging to 137 

 genera and 59 families. 



C. tabescens has been isolated from roots of 156 plants, comprising 

 90 species, from various parts of Florida, and a number of isolations 

 are reported from other States. 



While this fungus commonly may live a saprophytic existence for 

 years, it may also function as a virulent parasite and is capable of 

 attacking uninjured roots of the most vigorously growing plants and 

 spreading to adjacent ones, especially when closely planted. Its prin- 

 cipal mode of transmission appears to be by root contact. Infected 

 oak and other hardwood roots left in the land at the time of clearing 

 have been found to constitute sources of infection to planted trees 

 and shrubs for a much greater number of years than is generally 

 believed. 



The successful infection of Australian pines (Gasuarina spp.), 

 through both the use of pieces of naturally infected roots and pure 

 cultures of this fungus grown on lengths of oak stems placed in contact 

 with uninjured roots, is reported. In both cases the fungus was 

 reisolated and carried to fruiting. 



The incidence of Clitocybe root rot coincides to a large extent with 

 the location of areas where hardwood timber, especially oak trees, 

 occurred or was prevalent prior to clearing. In Florida, this disease 

 has been found to occur most frequently in well-drained, light, sandy 

 soils, which are dominantly acid in reaction and droughty in char- 

 acter, though it also occurs on clay soils in western Florida and 

 Alabama, which likewise are acid. As a rule it occurs much less 

 frequently on low hammock soils in Florida, which usually are neutral 

 or alkaline, and is unknown on the alkaline limestone land of Dade 

 County, even though oak and other hardwood trees occur in places. 

 This and the fact that the disease sometimes occurs on land that has 

 been cleared for many years and is free from old roots indicate that 

 some factor or factors other than the presence of roots in the ground 

 serving as sources of infection are involved in its incidence. 



Preventive and remedial measures for the control of Clitocybe 

 root rot are discussed. Surgical treatment and exposure of the root 

 crown to aeration and drying have proved effective in combating the 

 disease. Banking the soil to a point well above the partially girdled 

 bases of treated trees, to stimulate the development of new root systems 

 from the callus formed at the margin of the living bark, has been 

 found to expedite materially the recovery of trees greatly weakened 

 by loss of roots and partial girdling. 



