Biocontrol of Meloidogyne incognita and Vegetative Growth Stimulation in Tomato ‘Moneymaker’ Plants by Egyptian Soil Bacteria

Abstract Background Tomato yield is significantly reduced by root-knot nematodes (RKN; Meloidogyne spp.), particularly in tropical and subtropical regions. This study evaluated 20 bacterial isolates (B1–B20), belonging to the genera Bacillus, Lysobacter, Paenibacillus, and Streptomyces, from Sekem farms in Egypt for their potential to biocontrol RKN and stimulate plant growth in tomato ‘Moneymaker.’ The bacteria were compared to well-known microbial biocontrol agents (MBA), including Rhizobium etli G12 (B21), Pseudomonas trivialis 3Re2-7 (B22), Sporosarcina psychrophile Sd4-11 (B23), and B. subtilis Sb1-20 (B24), and a negative control, Escherichia coli JM109 (B25). The study involved seed-coated and -uncoated plants with bacterial isolates, planted in plastic pots, and inoculated with 1500 M. incognita J2 individuals per pot. Plants were grown in a saran-house during the 2022 and 2023 fall seasons, and their RKN-satisfying response (number of galls: NG and egg masses: NEM), vegetative growth, and metabolic activity were assessed 45 days after inoculation. Results In seasons of 2022 and 2023, seed coating with bacterial isolates achieved a significant improvement in plant growth (coefficient of variation: CV ranging 26.8–120.2% in 2022 and 10.9–48.8% in 2023) and a reduction in RKN-satisfying response (CV for NG: 57.6 and 53.8%, respectively; and for NEM: 56.5 and 65.3%, respectively). Compared to uncoated-seed plants, the bacterial seed coating reduced NG by 0.66–74.09% in 2022 and 14.61–66.29% in 2023. Similarly, NEM decreased by 0.63–70.61% in 2022 and 41.91–77.46% in 2023. The coated-seed plants by Bacillus subtilis subsp. spizizenii (B5), Streptomyces subrutilus Wb2n-11 (B12), Streptomyces scabiei (B19), and Bacillus mojavensis (B20), along with the well-known MBAs B22 and B23, showed increased photosynthetic pigments, fresh weight of roots and shoots, stem size, and number of leaves. This growth has also led to higher dry weights in roots and shoots, and an increase in the root content of carbohydrates and proteins. Seed coating induced systemic RKN resistance by increasing polyphenols in the root. In contrast, uncoated-seed plants showed reduced foliar photosynthesis pigment and metabolic activity due to high RKN damage. Principal component analysis revealed significant correlations among the evaluated traits. Hierarchical clustering categorized bacteria isolates into five clusters based on their impact on estimated plant traits. Conclusion B5, B12, B19, B20, B22, and B23 demonstrated superior performance in both controlling RKN and stimulating vegetative growth in tomato ‘Moneymaker’ plants as known MBAs.