Silício e fosfitos na resistência e tolerância a chrysodeixis includens e helicoverpa armigera (lepidoptera: noctuidae) em algodoeiro

Abstract

The application of silicon (Si) and mineral fertilizers to plants provides mechanical protection against herbivory due to its accumulation in plant cells, chemical protection through the production of metabolites that induce resistance to the action of pests and pathogens. Studies have been carried out to validate the effect of exogenous application of these compounds on the feeding and development of defoliating insects and recently on tolerance. The general objective of this work was to investigate the role of fertilization with Si (silicic acid), potassium phosphate (K) with addition of Si and copper phosphite (Cu) as elicitors of induced resistance to Chrysodeixis includens and Helicoverpa armigera, as well as in increased tolerance of cotton plants. In the first article, the soil application of Si doses in the induction of resistance and tolerance of cotton plants to C. includens and H. armigera was evaluated; the initial stage consisted of a dose-response test of Si on the biological characteristics of pests in the vegetative and reproductive phase of cotton. Fertilization with Si reduced survival and promoted weight reduction of caterpillars. Among the Si doses tested, 4 ton ha-1 was the one that stood out, being selected to continue the second stage of the work that evaluated the effect of Si application on cotton tolerance to C. includens herbivory; fertilization with Si increased the height and biomass of leaves, branches and roots, in addition to the leaf Si and chlorophyll content. In the second article, the application of mineral elicitors on the biological performance of C. includes and H.armigera caterpillars in transgenic Bt and conventional cotton cultivars was evaluated. The transgenic cultivars at the vegetative stage showed moderate resistance to C. includens, and fertilization with the products did not affect the biological performance of the caterpillars. In the cotton reproductive phase, the conventional cultivar provided larval survival of 43%, which differed from transgenic materials, which were below 7%. Transgenic cultivars at the vegetative stage expressed moderate resistance to H. armigera and fertilization with Cu phosphate provided the highest leaf consumption. Larval survival of H. armigera in the reproductive phase of cotton was significantly affected by cultivars; the conventional cultivar differed from the transgenic ones and provided 83% survival, while in the Bt cultivars, they were below 7%. Foliar application of K + Si phosphite reduced foliar consumption and reduced larval weight of H. armigera in the conventional cultivar. Significant effects were observed for the application of products based on K + Si phosphite and Cu phosphite on the dry matter of plants, being superior to the control and similar to each other. For root dry mass, the effects were significant for the elicitor and herbivory factors alone. The application of the products doubled the root dry matter, and the herbivory of C. includens stimulated an increase in the dry mass of the plant roots. New information can be used in integrated pest management, so that Si can act as an efficient elicitor and improve plant growth.