First report of Sphenospora kevorkianii (Raveneliaceae) on the orchid Catasetum fimbriatum in Brazil

Catasetum fimbriatum (Morren) Lindley is a commonly cultivated orchid found naturally in Brazil. In October 2001, cultivated C. fimbriatum plants from a commercial orchid nursery in the state of Rio de Janeiro (Brazil) were found to be attacked by a rust disease which rapidly disseminated to other plants.

The causal agent was identified as Sphenospora kevorkianii Linder, a rust fungus which was first reported from the orchid Epidendrum difforme Jacq. in Nicaragua (Linder, 1944). In Brazil, S. kevorkianii has been reported on Cyrtopodium punctatum (L.) Lindl., Notylia lyrata F. Moore, Prescottia sclerophylla Lindley, Stanhopea graveolens Lindley, Zygostates lunata Lindley (Hennen et al., 1982) and Pleurothallis mentigera Kraenzl. (Pereira et al., 2002).

Leaf lesions (Fig. 1) were either yellowish, due to the presence of a powdery mass of uredospores, or orange-brown, due to the abundance of dark orange coloured oil droplets, associated to the erumpent telia (Cummins & Hiratsuka, 1983). Lesions were observed on both leaf surfaces (Fig. 2).

Morphological features of the fungus (VIC 26509) were: Spermogonia and aecia unknown. Uredia amphigenous, subepidermal, becoming erumpent, 150 - 400 µm diameter. Uredospores ovoid, 26.5-31.5 x 17.0-24.0 µm, cell wall 1.5 - 3.5 µm thick, germ-pore indistinct (Fig. 3). Telia subepidermal, becoming erumpent due to the abundance of dark orange colored oil droplets, about 1 mm diameter. Teliospores ellipsoid, pedicelate, thin-walled, hyaline, 22.0-26.5 x 12.5 - 15.5 µm (Fig. 4). Paraphyses clavate, yellowish, 87-110 x 8-10 µm. Basidiospores were not observed.

Sphenospora kevorkianii has so far been reported only from three tribes of the subfamily Epidendroideae (Cymbidieae, Maxillarieae and Epidendreae) and only once from a member of Spiranthoideae. This is only the second report of S. kevorkianii attacking a member of Cymbidieae and the first on a species of the genus Catasetum.