Ácidos húmicos e rizobactérias como indutores de resistência a insetos pragas do feijoeiro

Abstract

Agricultural systems are constantly evolving and under attack from pests and diseases that result in lost productivity. The search for innovative and alternative methods to chemical control is increasingly relevant. Applicable to integrated pest management tactics, plant biostimulants are used in order to improve agronomic characteristics and induce resistance and tolerance to pests in plants, making them less susceptible to biotic and abiotic stress. In this context, the present work investigated the effects of the application of plant growth promoting rhizobacteria (RPCP) and humic acid (HA), isolated and together, in the induction of resistance against the main pests of common bean, the false caterpillar (soybean looper) Chrysodeixis includens (Walker) (Lepidoptera: Noctuidae) and the whitefly Bemisia tabaci Middle East-Asia Minor 1 (Gennadius) (Hemiptera: Aleyrodidae), respectively a defoliating and a sap-sucking insect. Common bean seeds cv. Carioca type pearls were inoculated with Rhizobium tropici CIAT899 and humic acid was applied to the soil by drench. In order to investigate the behavior and biology of the two pests in response to plants treated with RPCP, AH and RPCP + AH, a choice and no-choice bioassays were performed. In the choice trail, there was a greater number of visits by adults and of whitefly eggs in plants treated with RPCP and RPCP + HA compared to control plants, without the application of biostimulants. However, in a no-choice trial, the viability of whitefly eggs was reduced by 37% in plants treated with HA, and the total population of nymphs was reduced 2.4, 1.7 and 1.6 times in the treatments AH, RPCP + AH and RPCP, respectively. Newly hatched C. includens larvae did not discriminate the treatments with the choice and no-choice trials. Although the larval weight gain was similar in the different treatments, the larvae consumed smaller amounts of plants treated with RPCP and AH + RPCP compared to control plants in the no-choice trial. These results suggest that treatment with AH or RPCP improved the resistance of bean plants, mainly against B. tabaci. In addition, the application of RPCP increased shoot biomass. However, root biomass and chlorophyll a and b content were similar to those found in control plants. Besides being a potential tool to be added to integrated pest management in the agricultural production system, the use of isolated biostimulants may result in reduction of pesticide application, fertilization and, consequently, a reduction in the cost of production, in addition to preserving soil microbiota leading to a more balanced ecosystem, being applicable in conventional and organic crops.