Ethylene and nickel in the resistance of maize against the infection by Exserohilum turcicum

• Ano de defesa: 2020
• Autor(a) principal: Oliveira, Lillian Matias de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Milho- Doenças e pragas; Metabolismo; Hormônios vegetais; Plantas - Nutrição; Fotossíntese; Fitopatologia
• Link de acesso: https://locus.ufv.br//handle/123456789/27913

Diseases cause a negative impact on maize yield worldwide, and the northern leaf blight (NLB), caused by the hemibiotrophic fungus Exserohilum turcicum, is one of the most important. Considering the harmful effects of E. turcicum infection in the leaves of maize plants, the objectives of this study were to investigate the alterations in the photosynthesis (parameters related to leaf gas exchange and chlorophyll a fluorescence), the foliar concentration of micronutrients, and reactive oxygen species (ROS), production of ethylene, activities of both defense and antioxidant enzymes, and the expression of the genes related to the production of hormones. The first study investigated the role of ethylene (ET) in increasing the resistance of maize plants against NLB at physiological, biochemical, and molecular levels. Maize plants were sprayed with ET, aminooxyacetic acid (AOA) (an ET inhibitor), and water (control). The ET application increased its concentration in the leaf tissues and contributed to the expansion of NLB lesions. Also, high NLB severity resulted in lower values for net carbon assimilation rate, stomatal conductance, transpiration rate, and maximum quantum yield of photosystem II (F v/F m) at advanced stages of fungal infection. Lower concentration of pigments and higher concentrations of malonaldehyde (MDA) and hydrogen peroxide (H2O2) were noticed for ET- sprayed plants infected by E. turcicum. Great NLB development in the leaves of ET-sprayed plants can probably be attributed to the lower activities of antioxidative (ascorbate peroxidase, glutathione reductase, and superoxide dismutase) and defense (chitinase, β-1,3-glucanase, lipoxygenase, and phenylalanine ammonia-lyase) enzymes. The second study was carried out to investigate the effect of foliar nickel (Ni) spray on the potentiation of maize resistance against E. turcicum infection by examining alterations at biochemical and physiological levels. In the in vitro assay, Ni efficiently inhibited the mycelial growth of E. turcicum. For Ni-sprayed and inoculated plants, there were higher foliar concentrations of manganese and Ni. These plants exhibited significant decreases of 33 and 24%, respectively, for NLB severity at 12 and 16 days after inoculation. There were lower MDA and H2O2 concentrations in the leaves of +Ni inoculated plants. The decrease in NLB severity for Ni-sprayed plants was related to its direct effect against E. turcicum infection or through the potentiation of host defense responses such as high lipoxygenase and polyphenoloxidase activities as well as great production of phenolics and lignin. Keywords: Antioxidative metabolism. Host defense responses. Northern leaf blight. Plant nutrition. Plant hormone. Photosynthesis.