Aqueous extract of spent hops suppresses root-knot nematode and enhances soil biological activity

Abstract

Hops are known worldwide for their medicinal and antimicrobial properties, but their applications have been little studied in the field of agriculture. Furthermore, there are few studies about the nematicidal effect of the generated hops residue by the brewing industry. This study aimed to evaluate the potential of a 5% aqueous extract of hops residues in controlling Meloidogyne javanica in tomato plants and assess its impact on soil biological activity. Two experiments were conducted at different times. In both experiments, tomato seedlings grown in pots in a greenhouse received an application of 5% sent hops extract or water (control), using a spray volume of 50 L/ha. The treatments were applied in a hole made in the soil, close to the root system of the plant, approximately 2 cm deep. Plants were then inoculated with 1,000 eggs + eventual second-stage juveniles (J2) of M. javanica/plant, depositing the suspension containing the nematodes in the same hole made in the soil. In the laboratory, in the first experiment, basal respiration, soil microbial biomass, and nematode reproduction were determined at 30 days after inoculation (DAI), and in the second experiment, M. javanica reproduction was evaluated at 30 and 60 DAI, while basal respiration and soil microbial biomass were evaluated at 60 DAI. In the first experiment, the extract reduced total nematode number and number of nematodes per gram of root by up to 70% and 82%, respectively. In the second experiment, the respective reductions were 71% and 83% at 30 DAI and 80% and 73% at 60 DAI. The results showed that, in general, soils under plants treated with spent hop extract had higher basal respiration and microbial biomass carbon in both years, even when infected with nematodes. Thus, hops extract demonstrates potential for use in the management of M. javanica. However, further studies are necessary to elucidate the modes of action against these phytopathogens and their effects on soil.