Atividade de silício na produtividade e na indução de resistência de gramíneas ao ataque de pragas

Abstract

The use of the silicon element in agriculture contributes to the control of pests and diseases, besides positively affecting physiological factors. Its action has already been confirmed in several crops, especially for use in grasses. The objective of the present work was to evaluate the effects of silicon in the field: 1) in foliar application on productivity, physiology and induction of resistance in corn crop Spodoptera frugiperda (Smith); 2) soil application on the productivity, agronomic aspects, attraction to natural enemies and the induction of resistance of wheat plants to the aphids that attack the crop. The corn experiment was repeated twice in an area located in the municipality of Uberlândia - MG, in randomized blocks and a 4x2 factorial system (control without application and three sources of Si, and manual or non-S. frugiperda infestation). The experiment had four replications, constituting a total of 32 plots. The application of the products was carried out avoiding to reach the whorl of the plants, feeding place of the caterpillars, aiming to evaluate the systemic effect of the Si. Two evaluations of injuries caused by caterpillars were carried out, one immediately preceding the manual infestation of S. frugiperda and another at 15 days after infestation. At the time of harvesting, the plant height, number of ears per plot and, in the sequence the yield was estimated in t ha-1. The experiment with wheat was repeated concomitantly at three locations in Minas Gerais (in Uberlândia in the experimental area of UFU and IFTM, and in Montes Claros, in the experimental area of UFMG). Si was applied and incorporated to the soil 20 days before sowing of the two cultivars (BRS 264 and BRS 394) at a density of 80 seeds per meter in rows of five meters spaced 0.17 m apart. Weekly evaluations of the number of aphids per tree started 45 days after sowing, at which time the first individuals were observed. It was also evaluated the occurrence of parasitism and productive characteristics, such as plant height, productivity at t ha-1 and hectoliter weight. In the experiment with corn, for the first sowing season, there was no effect of the manual infestation of S. frugiperda on defoliation. However, in the second season, greater defoliation was obtained in the plots with manual infestation of this insect. Photosynthesis and transpiration were higher for the plants in which product 3 was applied than on plants without application of products (control). Reduction of photosynthesis and transpiration was observed in plants with manual infestation of S. frugiperda, regardless of the application of the products. There was no change in the injuries caused by S. frugiperda or influence on the productivity factors evaluated in maize plants with the application of the source products of Si. In the wheat experiment, the species Sitobion avenae (Fabricius) was obtained in the three localities. Schizaphis graminum (Rondani) was observed in high populations only in Montes Claros. UFU was the site where the highest number of S. avenae were obtained per tiller for both cultivars, while in Montes Claros the lowest populations were obtained. No parasitoids were obtained in Montes Claros, while UFU was the site that presented the most mummies per tiller. Thus, it was concluded that the application of silicon did not influence maize and wheat productivity, the sources of applied Si were not efficient in inducing resistance to S. frugiperda in maize plants and that the application of Si via soil was not able to affect the induction of resistance of wheat plants to aphids.