Control of Meloidogyne javanica and induction of resistance-associated enzymes in soybean by extracts of Ascophyllum nodosum

Abstract

This study investigated the ability of an aqueous extract of Ascophyllum nodosum to directly control the root-knot nematode Meloidogyne javanica and induce nematode resistance in soybean. In a first experiment, soybean plants were inoculated with 2000 eggs and juveniles of M. javanica and treated with extract doses of 0 (control), 25, 50, 75, and 100 g L−1 by two methods of application, soil drenching and foliar spraying. A second experiment evaluated the effect on the hatching percentage of 500 M. javanica eggs. A third experiment assessed defense enzyme activity in inoculated and uninoculated plants treated with A. nodosum extract (75 g L−1) by soil drenching or foliar spraying. This experiment was performed once and analyzed in duplicate. Inoculated and uninoculated untreated plants were included as controls. High extract doses (75 and 100 g L−1) promoted a 65% reduction in nematode population density in soybean. At doses of 32 g L−1 or higher, extract application by soil drenching increased shoot dry weight and plant height. The minimum dose of algal extract to obtain hatching percentages close to 0% was 21.8–22.2 g L−1. Peroxidase, polyphenol oxidase, phenylalanine ammonia-lyase, and glucanase activities were highest in uninoculated drench-treated plants at 12 days after treatment. A. nodosum extract was effective in reducing M. javanica population density in soybean and in vitro egg hatching. The use of the extract also offered potential to the increase in the activity of enzymes related to plant defense in relation to inoculated and untreated control and the uninoculated and untreated control.