Sphenospora kevorkianii on the orchids Epidendrum paniculatum and Stanhopea graveolens newly reported in Argentina

Plants of Epidendrum paniculatum and Stanhopea graveolens were collected in May 2007 as part of a native orchids preservation project in Baritú National Park, a protected area of the Yungas subtropical forest located in the province of Salta (Northwestern Argentina).

Some plants showed symptoms of a rust disease (Fig. 1 and 2). Leaves presented small chlorotic areas dispersed on the upper surface. On the underside, numerous erumpent pustules were found, containing powdery masses of yellow urediniospores. The pustules later turned dark orange when telia were formed. Uredinia were found on both orchid species while telia developed only on E. paniculatum. Specimens have been deposited in the herbarium of the Instituto de Botánica del Nordeste (Stanhopea graveolens, specimen Salas and Terada 370; Epidendrum paniculatum, specimen Salas and Terada 204).

The causal agent of the rust diseases was identified as Sphenospora kevorkianii. Urediniospores were ovoid yellowish and echinulate (Fig.3). Morphology and dimensions of the uredinia and urediniospores from both species were similar to those reported by Linder (1994). The telia observed on E. paniculatum were subepidermal and erumpent, in which numerous clavate paraphyses were found besides the pedicelated teliospores, longitudinally one-septate, hyaline and thin walled (Fig. 3).

Sphenospora kevorkianii was first described by Linder (1994) on Epidendrum difforme from Nicaragua. It has been reported in Brazil on Stanhopea graveolens and other orchid species, such as Pleurothallis mentigera (Pereira et al., 2002), Catasetum fimbriatum (Pereira and Barreto, 2004) and C. maranhense (Soares da Silva and Barreto, 2006). These findings show that Sphenospora kevorkianii has a wide host range, in contrast to most rust species.

This is the first report of Sphenospora kevorkianii infecting E. paniculatum and S. graveolens in Argentina. This rust has been catalogued as a pest in Hawaii, the biggest orchid producer in the Americas, and is widely distributed in Brazil where chemical control in orchid nurseries is highly recommended to control the rust. The production of orchids in Argentina has greatly expanded in the last 15 years. Although still far from the scale of Brazil or Ecuador, the most important nurseries are now producing 50,000 plants per year. Epidendrum species are sought by growers because of their use in commercial hybrid development, while Stanhopea species are mostly collected by orchid enthusiasts for the rare beauty of their flowers. Whichever the case, care is to be taken for the rust disease not to spread as has happened in other countries.