2 CIRCULAR 853, U. S. DEPARTMENT OF AGRICULTURE 



fruiting bodies or cultural studies, particularly in the more northern 

 States, have been attributed arbitrarily to A. mellea. Since A. mellea 

 occurs in all States where C. tabescens may be found, this is an unsafe 

 procedure. A. mellea also occurs more or less frequently in parts of 

 northern Florida. Apparently, the higher temperature range in 

 Florida is more favorable for optimum growth of G. tabescens. 



HISTORY, HOST PLANTS, AND ECONOMIC IMPORTANCE 



Clitocybe root rot was reported first from Oklahoma in 1901 by 

 Wilcox (S3), 2 who stated that it had been destructive to apple, cherry, 

 and peach trees there for a number of years. He estimated that in 

 many cases whole peach and apple orchards had been destroyed by 

 this disease in 2 years. In addition, he found the fungus to be a com- 

 mon parasite and saprophyte on four species of oaks. 



Unfortunately, Wilcox considered the Oklahoma fungus as a distinct 

 species from the one that had been so well described previously from 

 Ohio by Morgan (14-) as Agaricus (Clitocybe) monaldelplius. purely 

 on the basis of slight differences in morphology and its parasitic habit 

 of growth, and named it G. parasitica. This fungus has been described 

 under various other names in the United States, although Bresadola 

 pointed out in 1900 (3) and again in 1928 (If) that he considered the 

 American plant synonymous with C. tabescens of Europe. It even 

 has been confused with Armillaria mellea, having been erroneously 

 regarded by some mycologists as an exannulate form of that fungus. 

 The writer (19) has reviewed the synonymy of G. tabescens, and 

 more recently (25) has presented the results of a comparative study 

 of the cultural characteristics of these two closely related root rot 

 fungi, clearly showing that they are distinct species. The fact that 

 Wilcox (.33) mentioned and illustrated the occurrence of black, shoe- 

 stringlike rhizomorphs in connection with Clitocybe root rot indicates 

 that both this and Armillaria root rot undoubtedly occurred in Okla- 

 homa and that these similar root rots must have been confused by him 

 in the absence of cultural studies. This is confirmed by a recently 

 issued host index of Oklahoma plant diseases (18) in which both G. 

 tabescens and A. mellea are listed as occurring on various plants in 

 that State. While Wilcox (33) in 1901 mentioned Clitocybe root rot 

 as occurring on four species of oaks in addition to fruit trees in Okla- 

 homa, Preston (18) in 1945 merely listed C . tabescens and its synonyms 

 as occurring on hickory (Gary a alba) . bur oak (Quercus macrocarpa) , 

 and blackjack oak (Q. marttandica) , in addition to apple, cherry, 

 peach, and grape. 



Faurot (7) reported observing root rot caused by toadstool-bearing 

 fungi to be of very common occurrence and a fatal disease of orchard 

 trees in some scetions of southern Missouri in 1902. Duggar (5. p. Ifll) 

 stated that he had observed the Clitocybe root rot fungus to occur 

 abundantly during favorable seasons at Columbia. Mo., on roots of 

 hickory and other deciduous trees but failed to observe its occurrence 

 in orchards, despite special effort to find it. The writer (19). who 

 found this fungus to be the cause of a previously undetermined root 

 rot of grapevines, as well as of orchard trees, in southern Missouri, 



2 Italic numerals in parentheses refer to Literature Cited, p. 24. 



