Nematicidal Activity of Lactic Acid Bacteria against Root-Knot Nematodes

Root-knot nematodes are economically important obligate parasites of plant root that parasitize more than 3000 species of plant. Lactic Acid Bacteria (LAB) are well known as strong producers for wide range of organic acids that have been suggested recently to possess a remarkable lethal effect on root-knot nematodes. In the present ‘study’ 37 LAB strains were isolated from soil and agricultural wastes by using MRS medium and screened for their nematicidal activity under lab conditions. Four bacterial isolates, recorded lethal effect on second stage juveniles by more than 94%, were selected and identified by molecular method. Further, the nematicidal activity at two concentrations (i.e 50 and 10%) of the most promising ten LAB cultures was screened. The nematicidal activity of LAB was positively correlated to the concentration of their suspension cultures.2S4 (Pediococcus pentosaceus MW558270), 2S5 (Pediococcus pentosaceus MW558883), 3S1 (Pediococcus pentosaceusMW558885) and 1A3 (Pediococcus pentosaceus MW558152) isolates showed significant mortality effect by 88.42, 87.37, 81.05 and 85.96%at the low concentration (10%), respectively. In order to confirm the relationship between organic acid production by LAB and their nematicidal activity, an artificial succinic acid, lactic acid, malic acid, acetic acid, and their mixtures were tested at concentration of 1% for their ability to inhibit juvenilesvitality. The mixture of acids induced the maximum mortality effect by 100% followed by lactic acid which recorded 99.66% mortality effect. The microscopic studies and the malformation pattern of the juveniles indicating that the nematicidal activity of LAB may be derived mainly from their natural organic acids mainly lactic acid.