Silício e herbivoria no metabolismo e resistência induzida em milho e sorgo

Abstract

The use of silicate fertilization is a promising tool for pest management because silicon (Si) acts as a resistance inducer, either by structural change of the plant or by the production of defense compounds, which may vary according to the type of herbivory. The objectives of this work were to evaluate the influence of silicon and herbivory on metabolism and induction of resistance in corn and sorghum. Two experiments were proposed, the first one with the objective of evaluating the effect of Si application via soil on the induction of resistance to Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae), on the accumulation of Si by the plant, the gas exchange, photosynthetic efficiency and plant metabolism and influence of Si on the yield of corn crop cultivated in the field with doses higher than 600 kg ha-1 of Si. The second experiment aimed to evaluate the chemical compounds produced by the sorghum plant related to resistance induction by Si and herbivory caused by chewing and sucking insects. The first experiment was carried out at the experimental farm of the UFU, with five doses of silicon (0; 600; 800; 1,000; 1,200 kg ha-1) x 2 types of infestation of S. frugiperda (natural; manual). In the second experiment, sorghum plants grown in pots were exposed to Si fertilization stimuli and/or herbivory by S. frugiperda caterpillars. Population growth of Rhopalosiphum maidis (Fitch) (Hemiptera: Aphididae) was verified in these plants and considered as a third stimulus. Leaf silicon content, polyphenol and FRAP were evaluted and metabolomics analysis was performed. The plants analyzed were compared with control plants, without stimuli. The application of silicon induced the resistance in corn plants to S. frugiperda under field conditions, reducing defoliation and increasing the content of this element in the leaf. In sorghum plants, previous herbivory by caterpillar in plants without Si induced resistance by antibiosis to R. maidis, probably related to the reduction in the concentration of compounds 236,1388 and 474.3718. Induction of resistance by antibiosis was also observed in plants with herbivory and Si, related to the change in the composition of compounds 186.0715; 236.1388; 294.1832; 304.2408; 311.2479; 474.3718 and 571.4608. The leaf Si content and metabolic activity were higher in sorghum plants that received, together, application of Si via soil and both herbivores. Si played an important role in inducing resistance in corn and sorghum plants, reducing defoliation by S. frugiperda under field conditions in corn plants, without interfering with productivity, and reducing the population of R. maidis in sorghum plants, promoting increased metabolic activity.