Resistência constitutiva e induzida por silício em híbridos de milho a Rhopalosiphum maidis (Fitch., 1856) (Hemiptera: Aphididae)

Abstract

The action of pest insects is one of the factors that can bring damages to corn. In this context, the corn leaf aphid, Rhopalosiphum maidis (Fitch., 1856) (Hemiptera: Aphididae), is a pest that has been gaining prominence, whose control is currently accomplished almost exclusively by insecticide applications, which can cause damage to the environment and select aphid resistant biotypes to the agrochemicals. In this way, the knowledge of commercial resistant hybrids and methods of induced resistance in plants to those insects are necessary, being silicon an alternative to chemical control. Although the effects of this element in the increase of resistance of plants is known to some species of insects, studies with R. maidis are scarce and the effect of silicon in hybrids with different constitutive resistance degrees is still rather known. The objectives of this study were to determine the constitutive resistance of corn hybrids to R. maidis and the accumulation and the induction of resistance of silicon in hybrids with different constitutive resistance degrees. Therefore, field level trials were installed to select resistant and susceptibility genotypes. Then, in order to determine patterns of susceptibility and resistance to the corn leaf aphid, a greenhouse trial was installed, with manual insect infestation, where its population growth was evaluated. In another experiment installed in greenhouse with the same hybrids, with and without silicon fertilization, was determined the level of this element in the dry matter of those germplasms. The induction of resistance was determined in trials with aphid standard resistance and susceptibility hybrids, selected in the previous testing, with manual and natural infestation of the pest, in plots with and without soil silicon fertilization. The results showed that corn hybrids presented different constitutive resistance degrees to R. maids. In the field, the hybrids BM8850, AS1625PRO and DKB310PRO were susceptible and P30F53H, STATUS VIP, BM9288, DAS2B587HX, DKB175PRO, AS1633PRO and DKB390PRO2 were the ones that presented the smallest percentage of plants with aphids, indicating that these hybrids were resistant to R. maidis. When the antibiosis was evaluated by the aphid population growth, in the green house trial, the hybrids AG7088PRO3 and DKB310PRO2 were susceptible and P30F53YH resistant to this aphid. In addition, corn germplasm differ on silicon absorption capacity, being AG7098PRO2, AG8677PRO2, AS1633PRO2 and DKB390PRO2 more efficient for this nutrient accumulation and STATUS VIP less efficient. The silicon fertilization, via soil, induced resistance in corn plants to R. maidis, reducing the natural population of the aphid regardless hybrid constitutive resistance degree.