Abstract:
Several plant species are known to reduce plant nematode diseases in soil via nematotoxic volatiles. In the present study, the effect of Volatile Organic Compounds (VOCs) emitted by leaves of Morinda citrifolia L. (‘Ahu”) on second-stage juveniles (J2s) of Meloidogyne javanica was determined as an in vitro assay. In separate experiments, 30-one-day-old-J2s in 1 ml of Sterile Distilled Water (SDW) were exposed directly to the VOCs emitted by dry and aqueous filtered leaf macerate (AFLM), and VOCs trapped for 72 h, in a closed glass vial at 30ºC. The juveniles which did not expose to volatiles represented the untreated controls. The effects of the VOCs were assessed 48 h after exposure to the volatiles based on the mobility, immobility and mortality shown by J2s. The experiment was replicated five times and repeated once. One-way ANOVA was performed for the data analysis using SAS statistical package.
In untreated controls, J2s showed 100% mobility. VOCs emitted from DLM caused 49% reduction in J2s mobility, while VOCs from non-accumulated and accumulated AFLM caused 89% and 95% reduction in J2 mobility, respectively. When J2s were exposed to the DLM, a significantly higher (P<0.0001) mobility in J2s (51% ±1.23) was detected compared to immobility (9% ±1.13) and mortality (40±0.99). In contrast, VOCs emitted from AFLM caused a significantly higher (P<0.0001) mortality and immobility in J2s than mobility. The maximum mortality of 83% (±1.05) was recorded with the accumulated AFLM while maximum immobility (31% ±1.58) was recorded with non-accumulated AFLM. The findings indicated that the VOCs emitted from leaves of M. citrifolia had a potential to affect survival and mobility of J2s of M. javanica indicating nematicidal and nemato-static activity. The effect of VOCs varied with the nature of macerate and mode of exposure.
