Effect of Successive Subculturing on Virulence, Growth, and Germination of Fungus Metarhizium rileyi for Biological Control of Fall Armyworm

Authors

• Joanna Marie E. Valeros, Microbiology Division, Institute of Biological Sciences, College of Arts and Sciences, University of the Philippines Los Baños, College, Laguna 4031, Philippines
• Trisha Anne P. Garcia, National Crop Protection Center, College of Agriculture and Food Science, University of the Philippines Los Baños, College, Laguna 4031, Philippines
• Noel G. Sabino, Microbiology Division, Institute of Biological Sciences, College of Arts and Sciences, University of the Philippines Los Baños, College, Laguna 4031, Philippines
• Marcela M. Navasero, National Crop Protection Center, College of Agriculture and Food Science, University of the Philippines Los Baños, College, Laguna 4031, Philippines
• Melissa P. Montecalvo, National Crop Protection Center, College of Agriculture and Food Science, University of the Philippines Los Baños, College, Laguna 4031, PhilippinesFollow

Publication Date

12-1-2025

Abstract

This study explored the impact of successive subcultures of Metarhizium rileyi (Farl.) Kepler, S.A. Rehner & Humber on its cultural traits, spore germination, and virulence against fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), a key pest in agricultural systems. The mass production of infective propagules is essential for effective biological control. Notable changes were observed in the texture and mycelial appearance of the fungus across subcultures. Initially, the fungus exhibited a powdery texture up to the 6th subculture. However, the fungal growth became fluffy and cottony by the 8th and 10th subcultures. Additionally, sporulation rates (7.05 × 10⁸ to 1.22 × 10⁸ spores/mL) and germination rates (88.60% to 16.20%) declined with successive subculturing. Despite these changes, M. rileyi effectively induced mortality in the 1st and 3rd larval instars of S. frugiperda across all subcultures up to the 10th. Up to the 4th transfer, subcultures maintained consistent cultural morphology, spore viability, and pathogenicity. These results underscore the importance of limiting subculturing to maintain the efficacy of M. rileyi as a biocontrol agent, offering essential insights for optimizing its use in managing S. frugiperda infestations.

Recommended Citation

Valeros, Joanna Marie E.; Garcia, Trisha Anne P.; Sabino, Noel G.; Navasero, Marcela M.; and Montecalvo, Melissa P. (2025) "Effect of Successive Subculturing on Virulence, Growth, and Germination of Fungus Metarhizium rileyi for Biological Control of Fall Armyworm," The Philippine Agricultural Scientist: Vol. 108: No. 4, Article 1.
Available at: https://www.ukdr.uplb.edu.ph/pas/vol108/iss4/1