Resistência de planta induzida pelo Silício à insetos-praga na cultura do milho: abordagem mecanística e aplicada

Abstract

The plant resistance mechanism to herbivorous insects conferred by the accumulation of Silicon (Si) results not only from the mechanical barrier provided by the deposition of Si in the epidermis, but also from the activation of induced chemical defenses. Recently, it has been shown that Si also increases the recruitment of natural enemies by changing the emission of plant volatiles induced by herbivory, since it acts as a priming agent or inducer of the jasmonic acid pathway, the main modulator of the herbivory-induced response. In the literature, there is a lack of studies that evaluate the role of plant volatiles in the resistance conferred by Si against herbivorous insects. Likewise, fieldwork is scarce despite being strictly important. In this context, the general objective of this work was to investigate the role of volatiles from corn plants fertilized with Si as a mediator in the direct and indirect induced resistance against the key pests of the crop, Dalbulus maidis (DeLong & Wolcott) and Spodoptera frugiperda (J.E. Smith , 1797). In addition to evaluating the potential of Si fertilization in the population control of pests and diseases in the field. In the first article, through behavioral and biological tests, we verified that fertilization with Si in maize promoted greater egg deposition and faster development of D. maidis in the first generation. On the other hand, fertilization with Si impacted the second generation of leafhoppers, which produced fewer eggs, probably due to the energy cost of the accelerated development of the first generation. Furthermore, fertilization with Si did not affect the composition of constitutive volatiles of the plants and, consequently, did not influence the olfactory preference of the leafhopper. In the second article, we verified that fertilization with Si altered the emission of volatiles induced by the herbivory of S. frugiperda, whose composition presented an exclusive compound, the terpene Neryl acetate, compared with the emission of unfertilized plants and damaged by S. frugiperda. This difference was probably responsible for the higher recruitment of the predatory earwig Doru luteipes (Scudder, 1876) by the emission of corn plants fertilized with Si and induced by herbivory in relation to volatiles induced by herbivory from unfertilized plants. In the third article, in field trials, fertilization with Si showed potential to control initial infestations of S. frugiperda. The population of D. maidis was not affected by fertilization with Si, however, it showed to interact positively with the application of the chemical insecticide belonging to the chemical group of neonicotinoids and pyrethroids, presenting higher averages in the treatments that received the application of the insecticide. Likewise, the population of earwig D. luteipes and most of the phytotechnical and physiological characteristics, as well as the symptoms of the diseases evaluated were not affected by fertilization with Si in the field. Thus, we conclude that Si fertilization acts on the induced resistance of the corn plant, directly affecting the biology and behavior of second generation D. maidis, and indirectly increasing the attractiveness of volatiles emitted by corn plants fertilized with Si for the predator D. luteipes. In the field, fertilization with Si showed to control initial infestations of S. frugiperda, however for D. maidis and the predator D. luteipes, we did not observe effects of fertilization with Si on the population of these insects.