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| Author(s): |
Manoel Penachio Gonçalves
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2021-02-12 |
| Examining board members: |
Lilian Amorim;
Maria Cândida de Godoy Gasparoto
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| Advisor: | Lilian Amorim |
| Abstract | |
The myrtle rust, caused by Austropuccinia psidii, has recently received attention of the international plant pathology community, due to the global distribution of this pathogen on a wide range of Myrtaceae host species. In Brazil most epidemiological data on myrtle rust was obtained from Eucalyptus, although A. psidii had been described from guava plants at first time. Despite the importance of this disease, there is little information on its epidemiology in guava plants and on the effects of abiotic stresses on its development. Ontogenic resistance to A. psidii, described in old leaves of Myrtaceae species, has also not been studied in guava rust. The objectives of this study were to quantify monocyclic components and its impacts on young and old leaves of guava plants, and also the effects of moderate water deficit on the disease monocycle. In order to achieve these objectives a series of experiments were performed, presented in this dissertation in two chapters. In the first chapter the monocyclic components of rust and gas exchange in young and old leaves of guava plants, both healthy or inoculated with A. psidii, were quantified along the time. Experiments were also conducted to evaluate the photosynthetic limitations imposed by A. psidii on young guava leaves. Old guava leaves were completely resistant to A. psidii infection and this resistance was not only related to the inhibition of urediniospore germination. In the young leaves, highly susceptible to A. psidii, there was a high density of lesions, high disease severity and high production of urediniospores. Young leaves inoculated with A. psidii presented a reduction in CO2 assimilation proportional to the disease severity. The photosynthetic reduction of diseased leaves was not due to stomatal limitations, but to limitations in biochemical and photochemical activities. The gas exchange presented similar values to both old leaves inoculated or not with A. psidii. In the second chapter, potted guava plants cv. Paluma were exposed or not to biotic stress (A. psidii) and abiotic stress (moderate water deficit), in a single or a combined situations. In order to evaluate the disease behavior and the damages caused to the guava plants, the monocyclic components of rust and gas exchange in guava plants were quantified. The density of lesions was higher in guava plants submitted to the combination of water deficit and inoculation with A. psidii than in guava plants inoculated with A. psidii only. However, only one experiment presented higher rust severity in the treatment with combined stresses than in the treatment without water deficit. In both experiments, the mean values of areas under the CO2 assimilation and transpiration curves were significantly lower in diseased guava plants exposed to water deficit than in those exposed exclusively to the pathogen. In conclusion, the high disease intensity in young leaves seems to compensate for the marked ontogenic resistance of old guava leaves, in which symptoms do not occur. The disease significantly reduces the relative photosynthesis in young leaves, while ontogenic resistance has no photosynthetic cost to the leaves. The combined effects of biotic and abiotic stresses on gas exchange in guava plants surpassed the effects of stresses applied alone. (AU) | |
| FAPESP's process: | 19/20409-7 - Water deficit impact on guava rust: monocyclic components and plant photosynthesis |
| Grantee: | Manoel Penachio Gonçalves |
| Support Opportunities: | Scholarships in Brazil - Master |