ATHELIA ARACHNOIDEA, THE SEXUAL STATE OF RHIZOCTONIA-CAROTAE, A PATHOGEN OF CARROT IN COLD-STORAGE

Athelia arachnoidea was collected during winter on dead leaves of deci duous trees in Oregon. Minute sclerotia (0.2-1.0 mm) were seen on hyme nia, whereas in culture sclerotia were much larger (1.0-5.0 mm). The p athogenicity, morphological characteristics, and temperature growth re sponses of the anamorphic state, were identical to Rhizoctonia carotae . The relationship between the sclerotial anamorph and the teleomorph was confirmed by DNA sequence of the internal transcribed spacers of t he nuclear ribosomal repeat unit. The sequences were homologous among the specimens of A. arachnoidea and the sclerotial anamorph from Orego n, A. arachnoidea and R. carotae isolates from culture collections, an d several isolates of R. carotae from carrot cold-storage facilities. Like R. carotae, A. arachnoidea produced abundant crystals of calcium oxalate on the hyphae, was pathogenic on carrot at 3 C, and caused cra ter rot symptoms equivalent in severity. Sclerotia of A. arachnoidea-R . carotae did not germinate under conditions suitable for eruptive ger mination in A. rolfsii. The DNA sequence of A. epiphylla from Europe w as identical (within 6 bp) to A. arachnoidea-R. carotae, whereas A. ep iphylla from North America varied by 34-46 independent base pair chang es. Athelia epiphylla and A. arachnoidea formed similar sclerotia. Con necting the Rhizoctonia root pathogen to the Athelia teleomorph links the disparate literatures on the natural history of this fungus and re veals significant insights into the epidemiology of the disease. Fibul arhizoctonia gen. nov. is proposed to encompass Rhizoctonia species wi th clamp connections, and the description of R. carotae and R. centrif uga are emended.