Influence of nano-encapsulated peppermint essential oil and biocontrol fungus on root-knot nematode suppression and plant resilience in Guar (Cyamopsis tetragonoloba L.)

The nematode Meloidogyne incognita is one of the most destructive root-knot nematodes, as it reduces yield potential and has a major impact on global agriculture. The aim of this study was to evaluate the performance of peppermint essential oil nanoparticles (100, 200, and 400 mg/L) in combination with the pathogenic fungus Pochonia chlamydosporia (1 and 2%) and the herbicide metam sodium in controlling the nematode Meloidogyne incognita in guar (Cyamopsis tetragonoloba L.). The application of both P. chlamydosporia at 2% concentration and peppermint NPs 200 ppm combined was the most effective treatment combination used in this study, producing the greatest level of effectiveness, which was 70.66% mortality of J2s. Furthermore, both P. chlamydosporia and peppermint NP treatments had a high degree of impact on reducing egg production and galls produced by the root-knot nematode, and over 80% suppression of the final nematode population in soil. NP treatments also promoted improved growth characteristics of plants and increased physiological parameters. Root length was increased by 44.66% by combining NP 100 ppm with P. chlamydosporia (2%). NP 400 ppm combined with fungal treatment had a greater effect on total antioxidant capacity. The application of these two therapies collectively resulted in a marked decrease in the levels of both the stress-associated metabolites, proline and malondialdehyde; electrolyte leakage; and increased relative hydration of tissues. Gas chromatography-mass spectrometry (GC-MS) analysis of the best NP 200 ppm + P. chlamydosporia 2% treatment contained α-pinene, limonene, 1,8-cineole, menthofuran, polgon and D-trans-β-caryophyllene. These findings suggest that integrating nano-based essential oil formulations with fungal biocontrol agents provides a sustainable and effective strategy for nematode control and enhanced plant resilience under biotic stress.