Comparative assessment of freshly cultured microbial bioproducts and a seaweed-based biostimulant for plant growth promotion and root-knot nematode management in capsicum and spinach in Kenya

Summary Root-knot nematodes (RKN; Meloidogyne spp.) are among the most damaging pathogens of vegetable crops worldwide. They damage roots and reduce yield, with their management becoming challenging because of their wide host range. This study evaluated three microbial bioproducts, Mytech ® ( Purpureocillium lilacinum ), Trichotech ® ( Trichoderma asperellum ) and Regain ® ( Bacillus subtilis ) and a seaweed-based biostimulant (Maximizer ® ) for growth promotion and RKN management in capsicum and spinach. The fungal and bacterial bioproducts were cultured to provide fresh inocula for each experimental trial. In RKN-free pot experiments, Mytech ® and Trichotech ® consistently improved plant height, shoot and root fresh weight and total plant weight in capsicum, whereas Regain ® and Mytech ® enhanced plant height, shoot fresh weight and total plant weight in spinach compared with the non-treated control. In RKN-infected pot experiments, where microbial bioproducts or the seaweed-based biostimulant were applied before nematode inoculation, all treatments using bioproducts and biostimulant improved growth parameters, although responses varied between crops and repeated experiments. All bioproducts and biostimulant treatments significantly reduced nematode infection in both crops. However, significant reductions in nematode density, number of galls and reproduction factor were observed only with Regain ® and Mytech ® in spinach. These findings indicate that microbial bioproducts and seaweed-based biostimulants can promote vegetable growth and reduce RKN infection, although their effects on nematode density are treatment- and crop-dependent. Further field validation of these products is needed to establish their effects on marketable yield and economic returns under farmer conditions.