Doses de silicato de potássio no crescimento populacional de Melanaphis sorghi (Theobald, 1904) (Hemiptera: Aphididae) e no teor de silício foliar em plantas de sorgo.

Abstract

Brazil holds the position of the third-largest sorghum (Sorghum bicolor L. Moench) producer in the world, as this crop displays high adaptability to climatic variability, drought conditions, and allows for an extended planting window. The widespread occurrence of Melanaphis sorghi (Theobald) in sorghum fields has emphasized the need to study methods for controlling the population of this insect pest, as it is recurrent across all developmental stages of the plant. Increasing plant resistance through silicon (Si) application has been reported to help reduce herbivore population growth. This study aimed to evaluate the effects of soil-applied potassium silicate at different doses on the population growth of M. sorghi and on foliar Si concentration in sorghum plants. The experiment was conducted in a greenhouse using sorghum hybrid B503, with plants enclosed in 700 mL plastic cup cages covered with organza fabric. Four treatments and two controls were used, each with eight replicates: four potassium silicate doses (50, 100, 150, and 200 kg ha−1), a potassium-balanced control, and a fertilization control based on soil analysis recommendations. Potassium chloride was added to all treatments and to the potassium-balanced control to equalize the amount of potassium with that provided by the highest silicate dose. To assess M. sorghi population growth, each plant was infested with four nymphs of different instars, and the number of individuals was counted 14 days after infestation. Foliar silicon content was quantified using the blue colorimetric method. The application of potassium silicate did not reduce M. sorghi populations, with no significant differences in aphid numbers across the tested doses and controls. The highest foliar Si concentrations were observed in plants treated with the highest silicate doses, following a quadratic response pattern with a peak between 100 and 150 kg ha−1. In this study, soil-applied silicon did not increase sorghum resistance to M. sorghi through antibiosis; however, foliar Si accumulation increased at higher soil Si doses.