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  • Title: Uromyces savulescui on statice (Limonium sinuatum) in the Americas and reevaluation of its reported geographic range.
    Author: Abbasi M, Rubio K, Gomez-Zapata PA, Díaz-Valderrama JR, Aime MC.
    Journal: Plant Dis; 2023 Sep 05; ():. PubMed ID: 37669170.
    Abstract:
    Limonium sinuatum (Plumbaginaceae) is the most commonly cultivated recognizable cut flower crop in the genus Limonium. It is known by several common names including statice and sea lavender, due to its lilac-colored flowers and the fact that it naturally inhabits mainly coastal areas (Mellesse et al, 2013). Limonium sinuatum is native to the Mediterranean, although as a popular garden plant, has been naturalized in other parts of the world including coastal areas of California (USDA NRCS 2020). Cultivated L. sinuatum is used in fresh and dry flower arrangements in the Americas, comprising approximately 20% of the floriculture cultivated area in Ecuador (Vega and Morales 2011; Abascal Cañas 2017). In December 2014, L. sinuatum plants in the public park "Baños del Inca" in Cajamarca, Peru (S 7 9'46"; W 78 27'53"), were found infected with a rust disease. The plants were scattered in the park but infection incidence was 100% as individual plants were all found to be infected (Fig 1). Based on the percentage of symptomatic areas, including the yellow halos around pustules, calculated with ImageJ (Collins, 2007) from field photographs, the disease severity was estimated to be 58.9% in average, ranging from 19.8% up to 90.0%. Uredinia were present on both sides of the leaves as well as on stems and were roundish, oblong, pulverulent, and cinnamon brown in color; urediniospores 25.5 to 35.0 × 22.5 to 31.0 µm, were globoid to ellipsoid; urediniospore walls were cinnamon-brown, 2.5 to 3.0 µm thick, densely verrucose, with 2 to 3 equatorial germ pores. Few telia were present on leaves; these were scattered roundish or oblong, and greyish in color; teliospores 26.5 to 41.0 × 16.0 to 25.0 µm, were ellipsoid to obovoid, mostly attenuated at the apex; teliospore walls were colorless, 2-3 µm thick at sides, and up to 10 µm thick at apex. Teliospores readily germinated in sori producing basidia and basidiospores (Fig. 2). The rust features and dimensions of rust spores are consistent with available descriptions of Uromyces savulescui Rayss (Guyot 1951; Vakalounakis and Malathrakis 1987). To confirm identity, a 576 bp region of the 28S subunit of the ribosomal DNA repeat was sequenced following previously published protocols and primers (Aime 2006, Aime et al. 2018). The resulting sequence (GenBank Accession No. OR291160) shared 99.83% (573/574 bp) identity with a sequence deposited as Uromyces limonii (DC.) Lev. (accession KY764194, BPI910295, Demers et al. unpublished) from L. sinuatum in Ethiopia. However, U. limonii produces orange uredinia, thin-walled yellow-orange urediniospores, teliospores with mostly light chestnut brown wall and infects different hosts (Savile and Conners 1951). It is likely that KY764194 represents a misannotated record of U. savulescui. While Koch's postulates can be a useful tool for establishing causality in certain infectious diseases, their use may be limited when it comes to rust diseases based on old herbarium specimens. In our case, due to the age of the specimen, which is almost nine years old, various other methods were employed to identify the pathogen. These methods included microscopic examination for morphological criteria of the urediniospores and teliospores, as well as molecular techniques like 28S rDNA sequencing. Rust disease on L. sinuatum has been previously reported in Ecuador but the causal agent was identified as a Puccinia sp. and reported that the rust was able to destroy entire plots in humid conditions (Vega and Morales 2011). Whether this report also represent U. savulescui is not certain, but given that the urediniospores of Puccinia species are generally 2-celled, it is unlikely. García-Hernández et al. (2008) reported U. limonii on Limonium spp. from Chile, and Coca (2020) also reported U. limonii on Limonium sp., from Bolivia. However, judging from the photomicrographs (Coca 2020), the rust in the latter report is definitely U. savulescui and not U. limonii. Uromyces savulescui has been previously reported from the Mediterranean region and the Canary Islands (Vakalounakis and Malathrakis 1987). To our knowledge there is no report of this rust in the Americas, excepting the probable misidentifications already listed herein. The specimen has been deposited in the Arthur Fungarium at Purdue University as PURN15037.
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