CLITOCYBE ROOT ROT OF WOODY PLANTS 15 



After repeatedly isolating G. tabescens over a period of several 

 years and carrying most of the isolates to the fruiting stage, there ap- 

 peared to be no point in making further isolations, except in the case 

 of inoculated trees or new host plants, though isolation of the fungus 

 is always of value, especially when there is a possibility that the 

 closely related root rot fungus Armillaria mellea may be involved. 

 0. tabescens has been isolated from root materia] of 156 plants, com- 

 prising 90 species, from various parts of Florida. In the writer's 

 extensive cultural work with mushroom root rot in Florida, only 2 

 instances, both at Gainesville, have occurred in which A. mellea was 

 isolated and in both it w T as suspected when roots were collected that 

 this fungus rather than G. tabescens was involved. 



The writer has also isolated G. tabescens from infected grapevines 

 in Missouri (19) and from five different kinds of trees in Alabama, 

 as reported earlier in this circular. During the course of his work 

 on Clitocybe root rot in Florida he compared isolates of this fungus 

 from a number of sources outside of Florida with Florida isolates, 

 and they were the same. Isolates from sand pear and tung-oil trees 

 in Louisiana were received from Dr. A. G. Plakidas of the Louisiana 

 Agricultural Experiment Station. Isolates from a Japanese cherry 

 (Prunus sp.) at Washington, D. C, and from a sporophore that de- 

 veloped at the base of an eastern redcedar (Juniperus virginiana) 

 at Arlington, Va., were received from Mr. Ross W. Davidson, of the 

 Division of Forest Pathology. 



INOCULATION EXPERIMENTS 



Various attempts to produce artificial infection with Clitocybe 

 tabescens have been made by the writer over a number of years, be- 

 ginning in 1931. The earlier attempts, which involved placing agar 

 slants from large test-tube cultures against roots, both injured and 

 uninjured, of native and exotic trees growing in woods and vacant 

 lots, of potted woody plants in the greenhouse, and of Australian 

 pine and citrus trees in buckets in a lath house were all unsuccessful. 

 The ineffectiveness of this method was probably due to the short life 

 of the inoculum in this unprotected state and to the relatively long 

 time required for the fungus to infect the host. 



It was not until after lengths of roots naturally infected by the 

 Clitocybe root rot fungus were placed underground in contact with 

 uninjured roots that infection took place, and even then several 

 months elapsed before noticeable lesions developed. However, the 

 writer's inoculation experiments were carried on under very droughty 

 conditions. Successful artificial infections of horsetail and scalybark 

 Australian pines (Gasuarina equisetifolia and G. lepidopliloia) finally 

 were obtained, both through the use of pieces of naturally infected 

 roots and pure cultures of the fungus grown on lengths of oak stems 

 placed in contact with uninjured roots. In both cases the fungus 

 was reisolated and carried to fruiting. Successful inoculation ex- 

 periments with this fungus also have been reported by Plakidas (17) , 

 who was able to infect small Pineapple pear trees by placing blocks 

 of wood, on which pure cultures of the fungus were grown, in con- 

 tact with freshly wounded roots. 



