First report of Myrtle Rust caused by Austropuccinia psidii on Myrcianthes pungens (O. Berg) D. Legrand in Paraná state, Brazil.

Myrcianthes pungens is a tree fruit native to Brazil, unknown to a large part of the population, with fruit consumed only locally. In October 2022, at the experimental area at Universidade Tecnológica Federal do Paraná (UTFPR) in the Dois Vizinhos city, Paraná State, Brazil, symptoms of the disease were observed on mature leaves and fruits of 17 trees. Fungal fructifications were observed in the form of bright yellow uredinia containing a large mass of urediniospores on the surface and on the leaves and fruits that resembled the structures typical of a Myrtaceae rust pathogen. Leaves colonized by the fungus showed deformations, turning dark and rapidly causing senescence. In the orchard, the fungus affected 80% of the trees, with a severity of 40 to 45%. Diseased fruits (10) and leaves (10) (from each tree) were collected from 17 trees from different positions in the orchard. The observed structures (optical microscope) were hyaline and globose urediniospores (n = 30) which had pointed echinulate ornaments throughout their surface (Cummins & Hiratsuka, 2003), (n = 30, 14.84 µm × 21.1 µm). These characteristics were similar to the morphological characteristics of the genus Austropuccinia previously described by Young et al. (2019). A strain was selected as a representative for molecular characterization and pathogenicity tests (accession no. APM001). For molecular identification, the internal transcribed spacer (ITS) region (Kroop et al., 1995), b-tubulin (TUB2), and translation elongation factor 1-alpha (TEF) (Machado et al., 2015) were amplified by PCR and sequenced. The sequences were deposited in GenBank (accession nos. ITS: OQ442638, TUB2: OQ506543, and TEF: OQ506542). Phylogenetic analyses using Bayesian inference grouped the isolate with the type species of Austropuccinia psidii with a high posterior probability (1.0). Pathogenicity tests used conidial suspensions (1x105urediniospores/ml). Four branches containing twenty leaves and two young asymptomatic fruits were individually inoculated with 1.5 mL of urediniospore suspension using a bottle with a spray nozzle cap. The branches were protected with perforated transparent plastic bags moistened with distilled water and incubated at room temperature (18 ºC to 25 ºC). Three replicates (pathogen and control) spread on different trees in the orchard were used in this experiment. After seven days, symptoms of rust appeared on the leaves and on the tenth day of the fruits, with morphological characteristics similar to those previously reported. Control branches showed no fungal growth. The inoculation test was repeated, confirming the symptoms. This is the first report of the incidence of rust caused by A. psidii on leaves and fruits of M. pungens in Paraná State. The importance of the disease is due to the high percentage of fruit loss due to rapid rot and drop caused by the pathogen attack.