New insights into the role played by nickel and picolinic acid in the rice-Bipolaris oryzae interaction

• Ano de defesa: 2020
• Autor(a) principal: Hawerroth, Caroline
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa; Fitopatologia
• Palavras-chave em Português: Arroz - Resistência a doenças e pragas; Plantas - Nutrição; Fotossíntese; Mancha parda; Folhas; Doenças; Micronutrientes; Fitopatologia
• Link de acesso: https://locus.ufv.br//handle/123456789/31037

Brown spot, caused by Bipolaris oryzae, is one of the most important diseases of rice worldwide. Considering the importance of the micronutrient nickel (Ni) on plant metabolism and the great potential of the non-host selective toxin α-picolinic acid (PA) to be used enhancing plant resistance against diseases, the present study aimed to investigate (i) the effect of Ni on increasing rice resistance to brown spot and (ii) the effect of PA spray on the photosynthetic performance of rice plants infected by B. oryzae and whether high concentrations of PA could affect brown spot development. For the first goal, rice plants were grown in nutrient solution non-amended (-Ni plants) or amended (+Ni plants) with Ni and non-inoculated or inoculated with B. oryzae. There were significant increases in foliar Ni concentration and lower disease severity for +Ni in contrast to -Ni plants. The foliar tissues of -Ni plants were massively colonized by hyphae of B. oryzae in comparison to the leaf tissues of +Ni plants resulting, therefore, in more cellular damage as indicated by the high malondialdehyde concentration. In general, the activities of the defense enzymes chitinase, β-1,3-glucanase, peroxidase, polyphenoloxidase, and phenylalanine ammonia-lyase showed the same pattern between -Ni inoculated and +Ni inoculated plants during B. oryzae infection. High peroxidase activity for +Ni inoculated plants occurred at the earlier stage of fungal infection. High lipoxygenase activity for -Ni plants may have contributed to disease development. The photochemical performance of -Ni inoculated plants (lower maximum photochemical efficiency of photosystem II (PSII) (F v /F m ) values) was much more affected in comparison to +Ni inoculated plants. High values for effective yield of the PSII (Y(II)) and electron transport rate (ETR) for +Ni plants indicated their efficiency in allocating the absorbed light energy to the photochemical process. For the second goal, rice plants were sprayed with PA at the concentrations of 0 (PA 0), 1 (PA 1), 3 (PA 3), and 5 mg mL -1 (PA 5). The in vitro assays showed that fungal mycelial growth was inhibited by PA in a dose-dependent manner, conidia germination was not affected, and conidial germ tube length only decreased for PA 5. The higher PA concentrations, PA 3 and PA 5, caused necrotic lesions on non-inoculated plants. The symptoms of brown spot were reduced by PA 1 and PA 3 in comparison to non-sprayed plants. Lesions originated from B. oryzae infection and PA toxicity overlapped for inoculated plants sprayed with PA 3 and PA 5. The photochemical performance of non-inoculated plants was hampered by PA 3 and PA 5. The high concentration of photosynthetic pigments and less impairment on the photosynthetic performance of inoculated plants sprayed with PA 1 were noticed based on the values of F v /F m , Y(II), yield for dissipation by down- regulation (Y(NPQ)), yield for non-regulated dissipation (Y(NO)), and ETR in comparison to inoculated plants non-sprayed with PA. In conclusion, these studies highlight the potential of Ni to increase rice resistance to brown spot through active participation of some defense enzymes, a robust antioxidative system, and a better photochemical performance and the potential of low concentrations of PA to decrease brown spot severity while preserving the photosynthetic capacity of the infected plants while the highest PA concentration did not seem to benefit B. oryzae infection. Therefore, either Ni or PA presents great potential for brown spot management in rice production. Keywords: Antioxidative metabolism. Brown spot. Foliar disease. Host defense responses. Micronutrient. Necrotrophic pathogen. Non-host selective toxin. Photosynthesis. Plant nutrition.