Nematicidal Activity of Bacillus thuringiensis and Trichoderma harzianum against Meloidogyne incognita under in Vitro Conditions

Abstract

Root-knot nematodes (Meloidogyne spp.) are a significant constraint to global vegetable production, causing severe yield losses due to their widespread distribution and extensive host ranges. The main aims of this study are to evaluate the nematicidal impact of three indigenous Trichoderma harzianum and Bacillus thuringiensis isolates to control root-knot nematodes, Meloidogyne incognita, under laboratory. Morphological, microscopic, and biochemical analyses confirmed the identity of the biocontrol agents and the target nematode species. All Bacillus thuringiensis isolates were identified as Gram-positive, rod-shaped bacteria producing oval endospores, and their biochemical profiles obtained using the VITEK-2 Compact system showed a 98% probability of identification as B. thuringiensis. The Trichoderma harzianum isolates exhibited typical morphological characteristics, including branched conidiophores, flask-shaped phialides, abundant conidia, and the presence of chlamydospores. The perineal pattern analysis of adult females revealed morphological features characteristic of Meloidogyne incognita, including a high and square dorsal arch with wavy striations, confirming species identity. In vitro bioassays revealed significant differences (p ≤ 0.05) between microbial treatments and control groups in terms of egg-hatching inhibition and second-stage juvenile (J2) mortality. All B. thuringiensis and T. harzianum isolates exhibited strong nematicidal activity against M. incognita. The B. thuringiensis isolate Sh.Sa.3 showed the highest ovicidal effect, with egg-hatching inhibition percentages of 95.33%, 91.67%, and 88.67% after 24, 48, and 72 h, respectively, and corrected inhibition values exceeding 87%. Similarly, the T. harzianum isolate Sh.Sa.6 demonstrated substantial egg-hatching inhibition, with corrected inhibition percentages above 81% across all exposure periods. Moreover, the highest J2 mortality rates were recorded for B. thuringiensis isolate Sh.Sa.3, reaching 86.67% after 72 h, followed by T. harzianum isolate Sh.Sa.6, which induced 76.00% mortality at the same exposure time. In contrast, the control treatments exhibited minimal effects on egg hatching and juvenile mortality.