Bioremediation potential of the entomopathogenic fungus Lecanicillium saksenae (Kushwaha) Kurihara and Sukarno

Abstract

The study entitled “Bioremediation potential of the entomopathogenic fungus Lecanicillium saksenae (Kushwaha) Kurihara and Sukarno” was carried out in the Biocontrol Laboratory for Crop Pest Management, Department of Entomology, College of Agriculture, Vellayani, from 2022 to 2024 with objective to evaluate the insecticide, fungicide, nematicide and herbicide degradation potential of the entomopathogenic fungus Lecanicillium saksenae in soil. Tolerance studies were carried out in vitro, using poisoned food technique, in Czapek Dox Agar (CDA) under carbon devoid, nitrogen devoid and phosphorous devoid conditions, to test the ability of the fungus to utilize these molecules from the pesticides. The pesticides selected for the study included the insecticides chlorantraniliprole 18.5% SC, fipronil 80% WG, quinalphos 25% EC, and chlorpyrifos 20% EC, the fungicides hexaconazole 5% EC, tebuconazole 25.9% EC, carbendazim 50% WP, the nematicides carbosulfan 25% EC,fluopyram 34.48% SC and the herbicide pendimethalin 38.7% CS. Tolerance was assessed based on growth and sporulation of the fungus in poisoned media and calculating the Tolerance Index. Among the tested insecticides, highest tolerance was exhibited to chlorantraniliprole 18.5% SC,(nitrogen deprived medium), where the radial growth of mycelia was 4.75 cm by the 21st DAI, which was significantly higher than in fipronil 80% WG (1.30 cm), while quinalphos 25EC and chlorpyriphos 20% EC completely inhibited the fungus. The spore count observed was also highest in chlorantraniliprole poisoned medium (2.09 × 10⁷ spores mL-1), which was on par with that of control (4.27 × 10⁷ spores mL-1).The corresponding spore load in fipronil was 1.51× 10⁷ spores mL-1.In phosphorus-deprived medium, it exhibited moderate tolerance to quinalphos 25% EC and chlorpyrifos 20% EC, radial growth being 1.62 cm and 3.45 cm, respectivelyat 21 DAI and spore counts of 1.109 × 10⁷ spores mL⁻¹and 0.987 × 10⁷ spores mL⁻¹. In the case of the fungicides, hexaconazole 5% EC, tebuconazole 25.9% EC, and carbendazim 50% WP and the nematicides carbosulfan 25% EC and fluopyram 80

34.48% SC, L.saksenae was completely inhibited. So also, the herbicide pendimethalin 38.7% CS completely arrested the fungus in carbon devoid medium but supported its growth in nitrogen devoid medium (6.21 cm) and sporulation (4.26×107spores mL-1). Tolerance Index calculated based on the ratio of colony extension growth rates in the presence and absence of pesticide concluded that,it was highest for pendimethalin 38.7% SC (80.91), followed by chlorantraniliprole 18.5% SC (61.88), chlorpyriphos 20% EC (44.95) and quinalphis 25% EC (21.11). Further, the bioremediation potential of L. saksenae was assessed by inoculating the conidial suspension into pesticide-treated soil. Pesticide degradation was determined by detecting the respective residues using GC-MS and LC-MS for a period of three months. Percentage removal of residues was highest in the case of pendimethalin 38.7% CS (74.2 per cent), followed by chlorantraniliprole 18.5% SC (70 per cent) and fipronil 80% WG (51.67 per cent). Assessment of microbial population in L. saksenae inoculated soil contaminated with tolerant pesticides, revealed that the bacterial, fungal, and actinomycete counts were higher compared to uninoculated soil, indicating the detoxification of toxic molecules in inoculated soil. The bacterial count in inoculated soil after four weeks of treatments was significantly higher in fipronil treated fungus inoculated soil (3.95× 106 CFU g⁻¹) while in the uninoculated soil, it was 2.35× 106 CFU g⁻¹. The actinomycetes count was also highest in fipronil treated soil (5.83× 104 CFU g⁻¹) while in uninoculated it was 2.40× 104 CFU g⁻¹. Soil arthropod population assessed for a period of four weeks indicated that the population of soil mites and collembola was more in inoculated soils (21.90 to17.1) compared to the uninoculated (16.6 to 12). The study highlights the bioremediation potential of L. saksenae as a promising agent for degrading insectides and herbicide in contaminated soils. Its role in sustaining microbial populations further reinforces its applicability in integrated pest management (IPM) and sustainable agriculture. Future research should focus on field-scale validation of these findings and explore potential synergies between L. saksenae and other bioremediation agents.