Combined effects of Ascophyllum nodosum seaweed extract and biological control agents on Meloidogyne javanica in soybean

This study aimed to investigate the efficacy of Ascophyllum nodosum extract, in combination or not with biocontrol agents, in the management of Meloidogyne javanica in soybean, assess treatment effects on soil biological activity, and determine the total phenolic content of the extract. The experiment was conducted according to a 5 × 2 factorial design, with three biocontrol agents (Bacillus methylotrophicus, Pochonia chlamydosporia, and Trichoderma harzianum), a chemical nematicide (abamectin, positive control), and an untreated (negative) control, each in the presence and absence of A. nodosum extract. Treatments included six replications. Nematode inoculation (2000 eggs + juveniles of M. javanica per plant) was performed at the time of sowing. Sixty days later, plants were evaluated for height, shoot weights, numbers of M. javanica eggs and J2 extracted from roots, and soil biological activity. Biological and chemical nematicide treatments were effective in reducing M. javanica multiplication. There was a synergic effect of A. nodosum extract on M. javanica multiplication for the treatments with A. nodosum + T. harzianum, A. nodosum + abamectin (Trial 1) and A. nodosum + P. chlamydosporia (Trial 2). B. methylotrophicus and T. harzianum treatments enhanced plant development and soil microbial biomass carbon. Higher values of soil basal respiration and metabolic quotient (qCO2) were observed in the A. nodosum + abamectin treatment. A. nodosum extracts at 75 g L−1 had a total phenolic content of 13 255 and 11 608 mg GAE 100−1 g in Trials 1 and 2, respectively.