Abstract
Essential plant oils contain biopesticides that could be used to control many crop pests. Tetranychus spp. are mites that cause damage to several crops and are primarily controlled by synthetic pesticides. Literature showed that mites can be controlled with essential oils of plants containing eugenol. In this work, we evaluated the bioactivity of basil (Ocimum basicilum) accessions for peanut-spider mites control based on molecular, biochemical and agronomic assays. RNA from four basil accessions, previously chosen by divergence genetic analysis, were used to estimate the expression of eugenol synthase (EGS I) transcripts, by semiquantitative and polymerase chain reaction (qPCR) assays. Chromatography was, thereafter, performed in order to estimate the eugenol concentration. Feeding bioassays were performed using basil leaf extracts in order to estimate oviposition and mortality of spider mites females. Finally, a validation assay was carried out in greenhouse, using peanut plants previously infested with spider mites and weekly sprayed with basil water-extract. One basil accession, OVRS, revealed high phytotoxicity to spider mite females, at 15% water-extract. The mortality rate was 75% and complete inhibition of fecundity was found in BOD assays. In the greenhouse assay, the most severe damage due to mite infestations was found to plant height, number of pods and pod yield, which were reduced to 28, 53 and 52% in non-treated plants (control). Considering that basil is a short-cycle plant, with easy reproduction and management, these results represent an accessible alternative to organic control spider mites in peanut.
Highlights
Synthetic pesticides are widely used to control pest crops due to high efficiency to plant protection
In previous bioassays using leaf-water extracts at 15%, the mortality rate of female spider mites were situated in 35% (OCG, OSP, ORRS) and 53% (OVRS). These results indicate that the organic components present in basil leaves were more soluble in ethanol
Despite the genetic improvements and tolerance of the new cultivars to spider mites, pesticides are still necessary as a control method
Summary
Synthetic pesticides are widely used to control pest crops due to high efficiency to plant protection. The indiscriminate use of these products has led to several damages to mammals' health such as neurological, respiratory and reproductive effects, and cancer and to increase pesticide resistance of insect-pests Several plants produce a high diversity of secondary metabolites with biopesticide properties, including many nitrogen-free and nitrogen-containing compound. These biopesticides could be an alternative source of plant protectants for farmers that do not have access to synthetic pesticides. These compounds are synthesized in either a tissue-, organ- or developmentalspecific way by specific biosynthetic enzymes (Facchini and De Luca, 2008)
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