Abstract
Among the most destructive pests affecting plant growth and yield worldwide are root-knot nematodes (Meloidogyne spp.). Currently, the shift from the use of chemical nematicides is trangressing globally towards choices such as organic nematicides extracted from plant substances. Plant secondary metabolites have been identified as compounds responsible for nematicidal activities in different plant species and are favored nematicidal agents because of their safe environmental record and affordability. Phytochemical screening, DPPH● scavenging capacity and nematicidal properties of eight different plant extracts under in vitro and greenhouse conditions were investigated against the egg mass hatching of the nematode, M. incognita. Four concentrations (0.2, 0.4, 0.6 and 0.8 mg/mL) with distilled water serving as a control were replicated three times and arranged in a completely randomized design (CRD) in an incubator at 25 ± 3 °C. The phytochemical analysis showed that the highest total flavonoids, condensed tannins and phenolic contents were found in Vernonia colorata (88.71 mg/g QE), Searsia lancea (406.16 mg/g CCE) and Pelargonium sidoides (175.95 mg/g GAE), respectively, with DPPH● scavenging IC50 values of 84.94, 14.40 and 6.64 µg/mL respectively. Our results further revealed that all treatments with increasing concentrations suppressed egg mass hatching after 72 h. Cucurbita maxima methanolic crude extract with DPPH● scavenging IC50 value of 168.20 µg/mL significantly reduced egg mass hatchability by 77–96% after 72 h. Under greenhouse conditions, results showed a significant (P < 0.01) inhibition of 97% on second-stage-juveniles penetration/establishment on tomato roots, with 100% root gall development inhibition on seedlings treated with V. colorata methanolic crude extract. In conclusion, all eight plant extracts showed promising nematicidal activity at 0.8 mg/mL.
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