Evaluating the effects of bio-stimulants on the management of root-knot nematodes and growth of spinach and capsicum

Spinach and capsicum are important vegetable crops that are highly vulnerable to root-knot nematodes (RKN), leading to significant yield losses and threatening food security. Chemical nematicides, though effective, pose environmental and health risks, underscoring the need for safer alternatives. Bio-stimulants represent sustainable solutions that can simultaneously promote plant growth and suppress nematode populations. The main objective of the study was to evaluate the dual role of selected bio-stimulants in enhancing plant growth and suppressing RKN populations. The specific objectives of the study were to assess the influence of Purpureocillium lilacinum (Mytech WP), Bacillus subtilis (Regain), Trichoderma asperellum (Trichotech WP), and Maximizer bio-stimulant on growth of spinach and capsicum and also to determine their potential in managing root-knot nematodes. The experiment used randomized complete block design under greenhouse conditions. Agricultural soil was prepared by mixing sand and loam in a 1:2 ratio and sterilized in an autoclave at 121 °C for 1 hour. Seedlings were soaked for 12 hours in microbial bio-stimulant solutions at a concentration of 10⁶ CFU/mL, while Maximizer was applied at the manufacturer’s recommended rate of 8 mL per 20 L of water. Both spinach and capsicum received 10 treatments replicated 8 times, totaling 80 plants per crop. Root- knot nematode inoculation occurred 7 days after planting with 1500 nematodes per pot. Data on growth and nematode population were collected at 7-day intervals for 10 and 12 weeks and analyzed using one-way ANOVA followed by Tukey HSD test. The results demonstrated that application of these four bio-stimulants significantly (p≤0.05) improved plant growth and reduced root-knot nematode infestation compared to the control. Purpureocillium lilacinum enhanced spinach shoot and root weight by 60%. In capsicum, Purpureocillium lilacinum and Trichoderma asperellum increased fruit weight and fruit number by 117% and 150%, respectively. Regarding nematode disease suppression, both Purpureocillium lilacinus, and Trichoderma asperellum reduced final nematode population, and number of galls by over 35% and 50% in capsicum, respectively. In spinach, Trichoderma asperellum, and Bacillus subtilis achieved the highest reductions in final nematode population and number of galls by over 30% and 50%. While maximizer showed positive effects on growth and disease suppression in both crops, its performance was not prominent as the microbial bio- stimulants. In conclusion, the bio-stimulants significantly enhanced plant growth and reduced RKN infestation though effectiveness varied as no single bio- stimulant worked universally across growth parameters. Based on these findings, it is recommended to prioritize Purpureocillium lilacinum and Trichoderma asperellum for plant growth and Bacillus subtilis for nematode management. Furthermore, rather than single applications, a combination of different bio- stimulants should be advocated to increase synergistic effects. These should be integrated with other sustainable practices, such as organic amendments (biochar/manure) or resistant varieties.