The effects of zinc oxide nanoparticles and chitosanalginate coating on Pinus radiata: Fusarium circinatum interaction

• Autor(a) principal: Graça, Pedro Manuel Vieira Almeida
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/33369
• topic: Pine pitch canker; Pinus radiata; Zinc oxide nanoparticles; Chitosan coating; Resistance induction; Plant performance; Physiology

The rise of emerging diseases is a threat to forest sustainability worldwide. Pine Pitch Canker (PPC) caused by the pathogenic fungi Fusarium circinatum is an example of these diseases, for which there are no effective control measures available. The aim of this study was to evaluate foliar applications of Zn compounds, in ionic and nanoparticle (NP) forms, as a measure to control PPC. To attain our objectives, we performed in vitro and in vivo studies using ionic zinc sulfate (ZnSO4), zinc oxide NPs (ZnO NPs), and ZnO NPs coated with alginatechitosan (ZnO CNP). In vivo, foliar applications of the compounds at 20 mg Zn/L were made to Pinus radiata seedlings one and two weeks before fungal inoculation. Growth, physiological performance (water potential, gas exchange performance, lipid peroxidation, and antioxidant capacity), and essential inorganic nutrients content were evaluated right before inoculation. When 50% of the plants of a treatment group showed symptoms, the same parameters were evaluated except for inorganic nutrient content and with the addition of survival, electrolyte leakage, and relative stem necrosis. In vitro studies did not show relevant results, nor results that could be extrapolated to the in vivo situation. In the in vivo tests performed before inoculation, ZnO NP treatment improved gas-exchange parameters with a 17% increase in CO2 assimilation. ZnSO4 had no effects and ZnO CNP caused a 37% reduction of CO2 assimilation, as well as a reduction in stomatal conductance. Over time, the positive influence of ZnO NP was nulled and ZnO NP and ZnSO4 showed no differences compared to control. ZnO CNP reversed the negative effects reaching 34% more CO2 assimilation than control plants. With fungus inoculation, plants treated with ZnO NP and ZnSO4 caused no differences in the normal symptom’s appearance. ZnO CNP treated plants had symptoms emergence 6 days before control and showed a tendency of decreased relative necrosis. These results may have been caused by the low performance of the plants on the day of inoculation and also by an earlier occlusion of the vascular vessels, possibly caused by the influence of chitosan on the plant’s defense system. The results of the gas exchange parameters showed that Zn applied in the form of ZnO NPs has advantages over the ionic form. In the interaction, P. radiata – F. circinatum, only ZnO CNP had an impact where the chitosan coating may have caused the earlier onset of disease symptoms. Our results reinforce the need to better understand the mechanisms that regulate the effects of the application of Zn NPs in Pinus radiata plants, and particularly to understand the mechanisms of action of chitosan on plant health, exploring different dosages, timings, and pathosystems.