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Updated: May 15, 2026
Development of Metarhizium anisopliae as a Mycoinsecticide: From Isolation to Field Performance
Published on: July 30, 2017
Influence of some parameters on the germination assessment of mycopesticides
Rogério B Lopes1, Irene Martins, Daniela A Souza
1EMBRAPA Genetic Resources and Biotechnology, Parque Estação Biológica, W5 Norte (final), 70770-917 Brasilia, DF, Brazil.
Abstract:
The substantial negative impact of some parameters on the germination of low-quality conidia (high proportion of slow-germinating propagules) was demonstrated, whereas for high-quality batches their effect was small or even absent. Germination was increased as the initial hydration status of conidia immediately prior to suspension preparation was increased, being ca. 33% and 80% for dehydrated Metarhizium anisopliae propagules (water activity ≤0.314) from low- or high-quality batches after an 18 h incubation period, respectively, and 63% and 95% for hydrated propagules (water activity = 0.933). Germination of low-quality propagules also increased as the time dry conidia were kept in aqueous suspension prior to inoculation onto culture media (15 min, 3 or 24 h) or the incubation time at 25°C before counts (18, 48 or 72 h) was increased. Depending on treatment conditions, average germination of low-quality conidia varied from 53% to 98%. On the other hand, germination for high-quality conidia was always ≥94%. Regarding the relative humidity (RH) of the incubation atmosphere, the average germination rates for low-quality conidia on Potato Dextrose Agar (PDA) in Petri plates was 49%, while germination of these conidia on PDA blocks kept under lower RH inside plastic boxes was ≤23%. Use of lactophenol-staining and/or use of coverslips had a negative effect when germination assessment was performed for low-quality conidia, resulting in distorted counts or increased standard deviations compared to high-quality conidial batches. The occurrence of dislodged conidia (ungerminated conidia outside the inoculation zone due to hydraulic pressure exercised by addition of stains and/or coverslips added to the substrate by the time germination is assessed) was common place, whereas dislodged conidia were not seen in treatments with high-quality batches. This work underscores the importance of a number of parameters that anyone working with low-quality fungi needs to be cognizant of in their research.
Insights
Optimizing fungal conidia germination requires careful consideration of conidia quality and environmental conditions. Hydration status, incubation time, and assessment methods significantly impact germination rates, especially for low-quality fungal batches.
Area of Science:
- Mycology
- Plant Pathology
- Microbial Physiology
Background:
- Conidia germination is crucial for fungal growth and infection.
- The quality of conidia (proportion of viable propagules) can significantly influence experimental outcomes.
- Understanding factors affecting germination is vital for accurate fungal research and application.
Purpose of the Study:
- To investigate the impact of various parameters on the germination of low-quality and high-quality Metarhizium anisopliae conidia.
- To identify critical factors influencing conidia germination success.
- To provide insights for optimizing experimental conditions in fungal research.
Main Methods:
- Conidia from low- and high-quality batches were subjected to varying hydration levels (water activity) and incubation times.
- Germination assays were conducted under different relative humidity conditions.
- The effect of assessment methods, including lactophenol-staining and coverslip use, was evaluated.
Main Results:
- Initial hydration status and incubation time significantly improved germination of low-quality conidia.
- High-quality conidia consistently showed high germination rates (≥94%) across treatments.
- Low relative humidity and certain assessment methods (staining, coverslips) negatively affected low-quality conidia germination.
Conclusions:
- Conidia quality is a critical determinant of germination success and response to environmental factors.
- Optimizing hydration, incubation, and assessment methods is essential for accurate germination studies, particularly with low-quality conidia.
- Researchers must be aware of these parameters to ensure reliable results in fungal research.
