First Report of Myrtle Rust Caused by Austropuccinia psidii in Campomanesia guazumifolia (Camb.) Berg in Brazil.

Abstract

Campomanesia guazumifolia is a Brazilian fruit tree that has ecological importance and the potential to be explored by the food and medical industries (Lima et al., 2011). In February 2019, in the experimental orchard at the Universidade Tecnológica Federal do Paraná, Dois Vizinhos city, Paraná State - Brazil, disease symptoms were observed on leaves, stems, and fruits of 22 C. guazumifolia trees. Yellow uredinia were observed on upper side of the leaves, stems, and flowers, which resembled typical uredinia of Myrtaceae rust. The pustules occurred mainly on young shoots, and on flowers, they infected their sepals. Over time, tissues colonized by the pathogen exhibited deformations and mummification occurred in infected fruits. In the orchard, the fungus affected 80% yield. Twenty diseased plant parts (from each of the eleven trees) were collected at different positions in the orchard. One strain were selected as a representative for morphological characterization, multilocus phylogenetic analysis, and pathogenicity tests. The structures observed were epiphyllous uredinia (leaves), united in small groups with hyaline and obovoid or obpyriform urediniospores, which presented echinulate ornaments, germinated pores in the subequatorial and inordinate positions (Cummins; Hiratsuka, 2003) (n = 30, 14.84 x 21.12 μm). The morphology of uredinia and urediniospores was similar to the morphological characteristics of the genus Austropuccinia previously described in Young (2019). For molecular identification, genomic DNA was extracted and the internal transcribed spacer (ITS) region (White et al. 1990), β-tubulin (TUB2) and translation elongation factor 1-alpha (TEF) (Machado et al. 2012) were amplified by PCR, and sequenced. Bayesian inference was used to reconstruct a phylogenetic tree, using MrBayes v. 3.2.1 (Ronquist et al., 2012). The multilocus phylogenetic analysis clearly distinguished the isolate APCG001 as Austropuccinia psidii separating it from all other species. The sequences were deposited in GenBank (accessions nos. ITS: ON003418, TUB2: ON568196, and TEF: ON437601). For pathogenicity tests, four healthy branches (20 leaves each) were sprayed with 2.5 mL of (APCG001) uredospore suspension (105 mL-1) and covered with a plastic bag in the orchard. The air temperature ranged from 16ºC to 25ºC. Sterile distilled water was used as a control. Three replications (pathogen and control) were performed on different trees. After 6 days, symptoms of rust appeared on the plants. Control branches did not show fungal growth. The inoculation test was repeated again, confirming the initial results. This is the first report of infection by A. psidii in C. guazumifolia trees in Brazil, causing rust, necrosis, and early senescence in fruits, leaves, and stems. Myrtaceae rust reduces the C. guazumifolia leaf area, affecting photosynthetic production and reducing fruit quality.