Behavioural response of Meloidogyne incognita to benzyl isothiocyanate

Abstract

Summary -The breakdown of brassicaceous plant material produces nematotoxic isothiocyanates (ITCs). However, after the incorporation of brassicaceous plant material into soil, many nematodes are likely to be exposed only to sublethal concentrations of these compounds. Although unknown, the effect of these low ITC concentrations on the behaviour of plant-parasitic nematodes could play a role in nematode suppression. To address this question, the behaviour of infective second-stage juveniles (J2) of Meloidogyne incognita was evaluated following in vitro exposure to sublethal concentrations of benzyl isothiocyanate (BITC). Behaviour was qualitatively and quantitatively affected. Overall nematode activity in treatment groups scored visually, and individual nematode movement frequencies, quantified by video assay, were each significantly reduced within 2 h of exposure to 0.01 mM BITC. All responses were dose dependent. Infectivity of BITC-treated J2 of M. incognita on soybean (Glycine max) was measured directly by root staining and gall rating, and indirectly by egg production. All experiments showed significantly reduced infectivity after treatment of J2 with 0.01 mM BITC. In addition, egg production was almost completely eliminated (<5% of control) by 0.03 mM BITC. The correlation between the effect of BITC concentrations on J2 activity and infectivity was positive, with decreased J2 activity and infectivity resulting in decreased egg production. BITC concentrations that do not cause mortality significantly affect the behaviour of M. incognita J2, indicating that sublethal concentrations contribute to the overall nematode suppression by brassicaceous green manures.

Mortality and movement behaviour of Bursaphelenchus xylophilus under different dosages of copper sulphate

“…To our knowledge, this is the first report on the behavioural changes in B. xylophilus produced by a nematicide. In a previous study, Zasada et al (2009) reported significant behavioural effect of benzyl isothiocyanate (BITC) on Meloidogyne incognita -significantly reduced infectivity was observed after treatment of second stage juveniles with 0.01 mmol/l BITC. In addition, egg production was almost completely eliminated (< 5% of control) by 0.03 mmol/l BITC.…”

“…Five different concentrations of copper sulphate solution were tested, and distilled water was used as the control. A 50 µl sample of fresh nematode suspension was dispensed into a 96-well plate (approximately 40 nematodes in each well); 200 µl aliquots of different concentrations of copper sulphate were then added to (Zasada et al 2009) was recorded hourly from 0 to 8 h (Table 1). All experimental treatments and controls were carried out as 4 replicates, and repeated 5 times.…”

Effects of benzyl isothiocyanate on the reproduction of Meloidogyne incognita on Glycine max and Capsicum annuum

“…To monitor behaviour, 10 μl aliquots of each suspension were transferred to a 96-well microtitre plate containing 100 μl of the corresponding BITC or DMSO solution per well. Nematode movement and behaviour during the 2 h exposure period were used to verify that J2 were affected by BITC as expected (characteristic reduction in head movement frequency and change from sinusoidal to rod-like appearance; Zasada et al, 2009). After 2 h, host plants were inoculated with 500 μl of suspended J2 (ca 1500 nematodes/plant).…”

“…This high toxicity of ITCs to soil-borne pests contributes to the strategy known as biofumigation, in which plant material is incorporated into soil for the purpose of releasing ITCs as part of a non-synthetic chemical pest management approach (Brown & Morra, 1987;Kermanshai et al, 2001;Gimsing et al, 2007). However, complex interactions within the soil and the chemical nature of ITCs can make exposure of plant-parasitic nematodes to ITCs somewhat problematic, and understanding nematode population suppression at sub-lethal doses becomes important to ITC practicality (Brown & Morra, 1997;Gimsing et al, 2007;Zasada et al, 2009). Exposure of Meloidogyne spp.…”

“…Exposure of Meloidogyne spp. (root-knot nematodes) to micromolar doses of ITCs, including BITC, resulted in behavioural and reproductive effects (Zasada & Ferris, 2003;Zasada et al, 2009), including significant reductions of infectivity on soybean, Glycine max (Zasada et al, 2009). Here we present the first report of using a sub-lethal BITC dose to suppress M. incognita infectivity and egg production on pepper, Capsicum annuum.…”