Red flesh guava cultivars planted in the State of São Paulo come from both formal breeding programs and informal selections made by producers, from seedlings obtained from seeds. The cultivars 'Paluma', which is the most planted in the state, and 'Século XXI' belong to the first group. The second group includes the 'Sassaoka' and 'Tailandesa' cultivars. Although guava rust (Austropuccinia psidii) is considered the most important fungal disease in the crop, there is no characterization of the level of resistance/susceptibility for any of these cultivars. The effects of climatic changes will probably lead to changes in the areas where different crops are planted, partly influenced by the incidence of pathogens. Thus, it is important to know the behaviour of different cultivars to the most important pathogens in each crop, so that planting recommendations can be made accurately in the different scenarios of disease occurrence. This project, which aims to determine the levels of susceptibility/resistance of guava cultivars to Austropuccinia psidii, belongs to the thematic project "2019/13191-5 Epidemiological components, damage characterization and control of tropical and temperate rust in a scenario of global climate change", recently approved by FAPESP. To achieve the proposed objectives, experiments will be carried out in greenhouses and in the field. The monocyclic components of guava rust will be evaluated in seedlings of the 'Paluma' and 'Século XXI' cultivars artificially inoculated in a greenhouse. The incubation and latent periods, the frequency of infection and the severity of rust will be evaluated, as well as the sporulation of the pathogen. The comparison between cultivars will be performed using multivariate analysis techniques. The progress of rust incidence and rust severity will also be quantified in the field in the cultivars 'Paluma', 'Século XXI', 'Sassaoka' and 'Tailandesa". The rates of disease progress, estimated by population growth models for each cultivar, will be compared and will also serve as indicators of the level of varietal resistance/susceptibility. In addition, a diagrammatic scale will be developed to assess the severity of rust on guava leaves.
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