The Potential of Philippine Photorhabdus and Xenorhabdus Strains in Pest Management
2023.09.19
Romnick A. Latina and Barbara L. Caoili
The increasing concerns on the risks of chemical pesticides in controlling insect pests and plant pathogens have urged many agricultural scientists to search for alternative management strategies to combat these pests. In the University of the Philippines Los Baños, particularly at the Tropical Phytonematology Laboratory and Insect Pathology and Molecular Biology Laboratory, Institute of Weed Science, Entomology and Plant Pathology under the College of Agriculture and Food Science, a group of bacteria has been studied for their insecticidal, antimicrobial and nematicidal properties. These bacterial group are the endosymbionts of the entomopathogenic nematodes (EPN) namely, Steinernema and Heterorhabditis. The isolated bacterial endosymbionts were identified as Photorhabdus luminescens (from Heterorhabditis) and Xenorhabdus indica (from Steinernema) (Figure 1). While it has been well-reported in several countries that these endosymbiotic bacteria (ESB) possess insecticidal, antimicrobial and nematicidal properties, they are under-utilized in the Philippines. Hence, pioneering local research in UPLB started to test the potential in vitro of the Philippine strains of Xenorhabdus and Photorhabdus spp. against root-knot nematodes, some fungal plant pathogens and fall army worm.
Laboratory bioassays have proven the strong inhibitory activity of X. luminescens and P. luminescens cell-free culture filtrates (CFCs) to some fungal plant pathogens such as Rhizoctonia solani (Figure 2), Lasiodiplodia and Colletotrichum. 50-100 % growth inhibition was observed on fungal pathogens exposed to these endosymbiotic bacteria.
Similarly, it has been demonstrated that X. indica CFCs also possessed nematicidal properties against the Meloidogyne incognita infective juveniles. The efficacy of X. indica CFC against root-knot nematodes ranges from 60-100% depending on the concentration used in the assay. Greenhouse testing using the 40-50% CFC concentration showed reduced gall formation in tomatoes infected with the root-knot nematodes. Aside from the ESBs, the EPNs harboring these endosymbionts were also proven to reduce penetration and consequently, galling index caused by root-knot nematodes (Figure 4).
As part of developing mitigation measures against the recent infestation of fall army worm (Spodoptera frugiperda) (FAW), the insecticidal properties of Xenorhabdus indica CFC was also investigated against this pest. Preliminary screening via larval feeding assay (corn leaf discs saturated with X. indica CFC) markedly showed feeding deterrence of second larval instars and recorded 60-70% mortality (Figure 5).
Continuous efforts to exhaust the utility of these endosymbionts are underway in the hope of developing an efficient and sustainable ESB-based technology that can be incorporated in integrated pest management.
REFERENCE
Alforja, S.I.R., Rico, P.M.B., Caoili, B.L. and Latina, R.A. 2021. Two Philippine Photorhabdus luminescens strains inhibit the in vitro growth of Lasiodiplodia theobromae,Fusarium oxysporum f. sp. lycopersici, and Colletotrichum spp. Egypt J Biol Pest Control. 31:108; https://doi.org/10.1186/s41938-021-00454-x
Felicitas, E. F. A., Caoili, B. L., & Latina, R. A. 2021. Antagonistic effect of Steinernema abbasi and Heterorhabditis indica Philippine isolates on root penetration and development of Meloidogyne incognita in tomato. Biocontrol Sci Technol 31(8), 865-876. https://doi.org/10.1080/09583157.2021.1898541
Romnick A. Latina and Barbara L. Caoili
The increasing concerns on the risks of chemical pesticides in controlling insect pests and plant pathogens have urged many agricultural scientists to search for alternative management strategies to combat these pests. In the University of the Philippines Los Baños, particularly at the Tropical Phytonematology Laboratory and Insect Pathology and Molecular Biology Laboratory, Institute of Weed Science, Entomology and Plant Pathology under the College of Agriculture and Food Science, a group of bacteria has been studied for their insecticidal, antimicrobial and nematicidal properties. These bacterial group are the endosymbionts of the entomopathogenic nematodes (EPN) namely, Steinernema and Heterorhabditis. The isolated bacterial endosymbionts were identified as Photorhabdus luminescens (from Heterorhabditis) and Xenorhabdus indica (from Steinernema) (Figure 1). While it has been well-reported in several countries that these endosymbiotic bacteria (ESB) possess insecticidal, antimicrobial and nematicidal properties, they are under-utilized in the Philippines. Hence, pioneering local research in UPLB started to test the potential in vitro of the Philippine strains of Xenorhabdus and Photorhabdus spp. against root-knot nematodes, some fungal plant pathogens and fall army worm.
Laboratory bioassays have proven the strong inhibitory activity of X. luminescens and P. luminescens cell-free culture filtrates (CFCs) to some fungal plant pathogens such as Rhizoctonia solani (Figure 2), Lasiodiplodia and Colletotrichum. 50-100 % growth inhibition was observed on fungal pathogens exposed to these endosymbiotic bacteria.
Similarly, it has been demonstrated that X. indica CFCs also possessed nematicidal properties against the Meloidogyne incognita infective juveniles. The efficacy of X. indica CFC against root-knot nematodes ranges from 60-100% depending on the concentration used in the assay. Greenhouse testing using the 40-50% CFC concentration showed reduced gall formation in tomatoes infected with the root-knot nematodes. Aside from the ESBs, the EPNs harboring these endosymbionts were also proven to reduce penetration and consequently, galling index caused by root-knot nematodes (Figure 4).
As part of developing mitigation measures against the recent infestation of fall army worm (Spodoptera frugiperda) (FAW), the insecticidal properties of Xenorhabdus indica CFC was also investigated against this pest. Preliminary screening via larval feeding assay (corn leaf discs saturated with X. indica CFC) markedly showed feeding deterrence of second larval instars and recorded 60-70% mortality (Figure 5).
Continuous efforts to exhaust the utility of these endosymbionts are underway in the hope of developing an efficient and sustainable ESB-based technology that can be incorporated in integrated pest management.
REFERENCE
Alforja, S.I.R., Rico, P.M.B., Caoili, B.L. and Latina, R.A. 2021. Two Philippine Photorhabdus luminescens strains inhibit the in vitro growth of Lasiodiplodia theobromae, Fusarium oxysporum f. sp. lycopersici, and Colletotrichum spp. Egypt J Biol Pest Control. 31:108; https://doi.org/10.1186/s41938-021-00454-x
Felicitas, E. F. A., Caoili, B. L., & Latina, R. A. 2021. Antagonistic effect of Steinernema abbasi and Heterorhabditis indica Philippine isolates on root penetration and development of Meloidogyne incognita in tomato. Biocontrol Sci Technol 31(8), 865-876. https://doi.org/10.1080/09583157.2021.1898541