Austropuccinia psidii, the causal agent of Myrtle rust, although endemic in the Americas, has recently received attention of the international plant pathology community, due to the global dissemination of this pathogen, which began in 2007, with its detection in Asia. Much new information has been released, from its taxonomic position - until 2017 the pathogen was classified as Puccinia psidii - to the risks for Myrtle that evolved in the absence of the pathogen. In Brazil, eucalyptus rust is the most studied disease, although this pathogen was reported for the first time on guava plants. However, there are no epidemiological studies for guava rust. It is known that most of A. psidii isolates from guava are unable to infect eucalyptus and, for this reason, the information available for eucalyptus rust cannot be extrapolated to guava. In this work we will quantify urediniospores germination of A. psidii in vitro and also will determine the monocyclic components of guava rust in vivo under different environmental conditions. The in vitro tests will be conducted in Petri dishes, in which suspensions of A. psidii urediniospores will be deposited and incubated for 2, 4, 6, 12 and 24 h, at temperatures of 10, 15, 20, 25, 30 and 35 oC. For in vivo tests, guava seedlings cv. Paluma will be inoculated with suspensions of A. psidii urediniospores and incubated for 6, 12 and 24 h in a humid chamber, in growth chambers with temperatures of 15, 20, 25 and 30 oC. The variables to be evaluated in young leaves are: latent period (days), frequency of infection (number of pustules / cm2 of leaf), lesion growth (mm / day), disease severity (percentage of symptomatic leaf area) and infectious period (days). This information will be valuable not only to understand the progress of the disease in different environmental conditions, but also to predict the geographic distribution of rust in different climate change scenarios. This work is linked to the thematic project 2019 / 13191-5 "Epidemiological components, damage characterization and control of tropical and temperate rust in a global climate change scenario", recently approved by FAPESP, whose main objective is the epidemiological assessment of tropical and temperate rusts under abiotic stresses.
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