Occurrence of rust in Myrcianthes pungens (O. Berg) D. Legrand caused by Austropuccinia psidii in the state of Rio Grande do Sul

Guabiju tree (Myrcianthes pungens) belongs to the Myrtaceae family, with wide occurrence in Rio Grande do Sul (RS), southern Brazil, demonstrates great commercial potential regarding the consumption of its fresh fruit, which has a sweet taste and can be used in drinks, jellies and ice creams, in addition to its nutraceutical properties. As their main characteristic, rusts present the formation of orange pus-tules containing urediniospores of the pathogen on affected organs. The action of the pathogen causes deformation of stems, leaves, flowers and fruits, thus interfer-ing with the physiological processes of the plant. Thus, the present work aimed at presenting information on the occurrence and confirmation of the causal agent of guabiju rust, in addition to reporting the accessions most susceptible and resistant to Austropuccinia in the guabiju working collection of Eldorado do Sul, RS, Brazil. The diagnosis of the disease was based on symptoms, observation of fungal struc-tures by light microscopy and molecular analyses. From microscopy, ellipsoid to ovoid and slightly equinulate urediniospores were observed, characteristic of Aus-tropuccinia sp. The sequence of the internal transcribed spacer (ITS) region of the isolate showed 99.06% similarity with sequences from the same region of A. psidii deposited on the nucleotide database -GenBank (NCBI). This is the first report of rust associated with guabiju in the state of Rio Grande do Sul, Brazil. From the dia-grammatic scale developed, it was possible to identify different levels of susceptibil-ity to A. psidii in guabiju accessions under study.

Automated summary

The Guabiju tree, a member of the Myrtaceae family, has great commercial potential due to its sweet-tasting fresh fruit, which can be used in various food and drink products. This research studied the occurrence and identification of guabiju rust, a disease that affects the plant's stems, leaves, flowers, and fruits. The study also identified the most susceptible and resistant guabiju accessions to the rust pathogen.