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First Report of Geranium Rust (Puccinia pelargonii-zonalis) in the State of Michoacán, México

Geranium is one of the most popular ornamental plants in México. In December 2012, rust symptoms were observed on leaves of common geranium (Pelargonium × hortorum L. H. Bailey) growing in pots in garden landscapes in Morelia, Michoacán. Dark brown pustules with chlorotic halos appeared on the lower leaf surface. A center pustule surrounded by one or more partial-to-complete concentric circles of smaller pustules was observed in each lesion. Urediniospores were globose or subglobose to ovoid, light brown, echinulated, thin-walled with two more or less conspicuous subequatorial pores, and 21 to 29 × 18 to 24 μm (25.5 × 22.8 μm average). Teliospores were not observed. Based on these characters, the rust was identified as Puccinia pelargonii-zonalis Doidge (1,2). Pathogenicity tests were conducted on three healthy P. × hortorum plants that were sprayed with water droplets containing urediniospores. The inoculated plants were covered with a plastic bag and placed in a screened house. The bags were removed after 24 h. Afterwards, the plants were maintained outside the screened house in full sun at ambient temperature (24 to 30°C in the day and 5 to 10°C at night). Initial symptoms were observed 15 to 17 days post inoculation. Symptoms appeared as small light yellow spots on the upper surface of mature leaves. Urediniospores production on the lower surface of the leaves was evident 22 to 25 days post inoculation. To our knowledge, this is the first report of P. pelargonii-zonalis in the state of Michoacán, México. Geranium rust has been previously reported only in the state of Guanajuato (2).

References: (1) E. M. Doidge. Bothalia 2:1, 1926. (2) H. L. Gallegos and G. B. Cummings. Uredinales (royas) de México. Vol. 1. Culiacán, Sinaloa, México, SARH, 1981.