Fungal entomopathogens as endophytes: can they promote plant growth?

ABSTRACT

Two experimental replicates were conducted to test whether strains of Beauveria brongniartii (BIPESCO2 and 2843) and Metarhizium brunneum (BIPESCO5) can endophytically colonise Vicia faba plants and improve their growth by comparing them with an endophytic strain of B. bassiana (NATURALIS^®). The plants were inoculated through foliar spray and the effect of inoculation on plant height, leaf pair number, fresh root and shoot weights was measured at 7 and 14 days post inoculation (dpi). Endophytic colonisation of different plant parts with the tested fungal strains were confirmed 7 and 14 dpi through re-isolation of inoculated fungi onto selective media and subsequent Simple Sequence Repeat (SSR) marker-based genetic identification. All tested strains were able to endophytically colonise leaves, stems, and even roots of inoculated plants 7 and 14 dpi, but per cent colonisation varied significantly among strains and plant parts within each sampling date. Foliar inoculation of plants with the tested strains increased plant height, leaf pair number, fresh shoot and root weights; however the increase was not always consistent across sampling dates in both experimental replicates. This study provides the first evidence for the endophytic colonisation of plants with two strains of B. brongniartii, an important biocontrol agent of Melolontha melolontha and other scarab beetles in several European countries, and thus extends previous reports on the ability of entomopathogenic fungi to act as endophytes. It also presents possible explanations for the lack of consistency in the plant growth promotion obtained by the foliar inoculation of entomopathogenic fungi.

KEYWORDS:

• Beauveria bassiana
• Beauveria brongniartii
• Metarhizium brunneum
• plant growth promotion
• SSR marker-based genotyping
• systemic plant colonisation

Acknowledgements

Both authors thank Dr Hermann Strasser (Institute of Microbiology, University of Innsbruck, Austria) for providing B. brongniartii strain BIPESCO2 and M. brunneum strain BIPESCO5, and Dr Anas Abdelqader (Department of Animal Production, The University of Jordan, Jordan) for his help with statistical analyses. Thanks are extended to Sonja Reinhard (Institute for Sustainability Sciences, Agroscope, Switzerland) for helping with SSR marker analyses. The comments of two anonymous reviewers and the Associate Editor are appreciated.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by an ‘International Short Visit’ grant (IZKOZ3_161554) from The Swiss National Science Foundation (SNF) provided to the first author.