The potential of using Metarhizium anisopliae and Metarhizium humberi to control the Asian soybean rust caused by Phakopsora pachyrhizi

ABSTRACT

Phakopsora pachyrhizi causes Asian soybean rust, resulting in severe losses of soybean yield. This study assessed the biocontrol efficacy of cell-free culture filtrates and conidial suspensions of Metarhizium anisopliae (MABR-01) and M. humberi (MHBR-03) against P. pachyrhizi in vitro and in planta. A 50% concentration of culture filtrates of M. anisopliae and M. humberi inhibited the germination of P. pachyrhizi urediniospores by 85 and 96%, respectively, compared to the 50% potato-dextrose broth (PDB) control. The conidial suspensions caused no inhibition of P. pachyrhizi in vitro, but the conidial suspension of M. anisopliae controlled the rust disease in plants with a 51% efficiency. Soybean plants colonised by M. anisopliae MABR-01 and exposed to P. pachyrhizi showed less severe disease in the shoots compared to plants not colonised by M. anisopliae; the disease was reduced by 40%. Spraying plants with 50 and 75% culture filtrates of M. humberi and a 75% concentration of M. anisopliae significantly reduced rust disease, by an average of 86%. Plants pretreated with Metarhizium culture filtrates showed a 30% reduction in P. pachyrhizi colonisation based on qPCR quantification of the pathogen genomic DNA. These results indicate a high biotechnological and sustainable potential of these two Metarhizium species for control of Asian soybean rust.

KEYWORDS:

• Biological control
• resistance inducers
• soybean rust
• entomopathogenic fungus
• biocontrol
• Glycine max

Acknowledgements

We thank the National Council for Scientific and Technological Development (CNPq, Brazil); São Paulo Research Foundation (FAPESP) and São Paulo Advanced Research Center for Biological Control (SPARCBIO) (FAPESP grant 2018/02317-5); and for a master’s programme grant to Sabrina Holz (grant 2018/18393-2 and 2019/19767-6) for financial support. We are grateful to Professor Zhi-Yuan Chen and Dr. Yenjit Raruange from Louisiana State University (USA) for their support in the qPCR analyses. We thank Professor Italo Delalibera Júnior from ESALQ/USP for providing the isolates of Metarhizium anisopliae (isolate MABR-01) and Metarhizium humberi (isolate MHBR-03); and Dr. Cláudia Vieira Godoy from Embrapa Soybean for the Phakopsora pachyrhizi isolate (PR_ASR01 isolate).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study received financial support from the National Council for Scientific and Technological Development (CNPq, Brazil) and the São Paulo Research Foundation (FAPESP, Brazil), grant numbers 2018/18393-2 and 2019/19767-6. Dr. Héros José Maximo thanks the São Paulo Research Foundation (FAPESP, Brazil) for support (grant number 2019/23030-9). The study conducted at LSU AgCenter was supported by Louisiana Small Grain Promotion Board (2019–2020).