Objective Entomogenous fungi are susceptible to strain degradation and reduced activity during the passage process. Selection of suitable strain preservation methods is a critical measure to reduce the passage of fungal culture in laboratory.

Method Three preservation methods (PDA slant, sand tube, and glycerin) were employed to preserve 13 species of entomogenous fungi (18 strains in total) for three periods of 3, 6, and 12 months. The preservation effects of the three different preservation methods were evaluated through comprehensive assessments including observing strain revival efficiency and detecting mycelial growth rate, dehydrogenase activity, and spore production.

Result When the preservation period was 3 months, except for several strains preserved by the sand tube method, all three methods demonstrated satisfactory preservation effects, with the PDA slant method showing superior results. Among these, 15 strains exhibited higher mycelial growth rates and dehydrogenase activities, while 12 strains showed higher spore production compared to other methods, and all the strains had good mycelial growth and normal color. When the preservation period was 6 months, the glycerol method demonstrated superior preservation effect. Among these, 14 strains exhibited higher mycelial growth rates, 15 strains showed higher spore production and all strains had better mycelial growth compared with other methods. Except for 6 strains in the PDA slant, the color of the other strains did not change. Among the mycelial dehydrogenase activities, 9 strains showed the best effect in the sand tube method. When the preservation period was 12 months, the glycerol method showed the best preservation effect, with minimal changes in colony color, mycelial growth rate, and spore production compared with those at the period of 3 months. Under the sand tube preservation condition, Metarhizium robertsii MrGX0603, Beauveria bassiana BbGX7303, Purpureocillium lilacinum PiGX0201, Cordyceps cateniannulata CcGX32S01 and C. fumosorosea CfGX4206 demonstrated superior preservation effects. These strains showed higher mycelial dehydrogenase activities, with recorded OD₄₉₀ values of 1.18, 1.17, 1.13, 1.12, and 1.27, respectively, and better spore production with recorded values of 53.50×10⁶, 52.23×10⁶, 62.00×10⁶, 54.21×10⁶, and 53.79×10⁶ spores/cm², respectively. The mycelial growth rate, dehydrogenase activity and spore production of the strains decreased slightly. The vitality indexes of 18 strains had decreased apparently after 12 months of preservation, and the preservation effect of sand tube method was better than that of PDA slants.

Conclusion Under the identical preservation methods and time frames, the preservation effects vary markedly among different strains. Different preservation methods can be selected according to the characteristics of the strains and preservation periods. The PDA slant preservation method is most suitable for short-term preservation of approximately 3 months. The glycerol method shows the best preservation effect for a 1-year preservation period. The sand tube preservation method is more appropriate for strains with sporulation quantities exceeding 50×10⁶ spores/cm².