Location: Pest Management ResearchTitle: Effects of endophytic entomopathogenic fungi on soybean aphid and identification of Metarhizium isolates from agricultural fields Author
|Clifton, Eric - Iowa State University|
|Hodgson, Erin - Iowa State University|
|Gassmann, Aaron - Iowa State University|
Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2018
Publication Date: 3/22/2018
Citation: Clifton, E.H., Jaronski, S., Coates, B.S., Hodgson, E.W., Gassmann, A.J. 2018. Effects of endophytic entomopathogenic fungi on soybean aphid and identification of Metarhizium isolates from agricultural fields. PLoS One. 13(3):e0194815. https://doi.org/10.1371/journal.pone.0194815.
DOI: https://doi.org/10.1371/journal.pone.0194815 Interpretive Summary: Recent studies have revealed a new role of certain fungi classically considered as insect pathogens — as endophytes, or organisms living within plants, often in some sort of symbiotic relationship with their host plant. A number of reports have also detailed adverse effects of such endophytic, insect pathogenic fungi on insects attacking those crop plants, indicating a new potential role for these fungi, one beyond mere spraying of fungus spores onto a crop with the intent of direct, fatal infections, as if the fungus was a biological substitute for a chemical pesticide. The present study examined whether two U.S.-registered and commercial fungi, Beauveria bassiana strain GHA and Metarhizium brunneum strain F52, could colonize soybean via a seed treatment route, and affect subsequent soybean aphid populations on those plants. While the GHA fungus had no effect on soybean aphid colonization of treated plants, soybean treated with Metarhizium F52, surprisingly increased the susceptibility and suitability of the plants for the aphid. Aphid populations were actually greater on Metarhizium-treated plants than the controls. This is the first such observation. The implication of these observations is that Metarhizium F52 treatment in soybean could actually have an effect reverse than intended, making aphid infestation worse. In addition, the authors examined the genetic profiles of 17 Metarhizium strains isolated from Iowa farm fields. DNA analysis revealed them to be all in one species, Metarhizium robertsii and closely related to one another, regardless of their derivation from different fields.
Technical Abstract: Terrestrial plants can harbor endophytic fungi that may induce changes in plants that in turn affect interactions with herbivorous insects attacking those plants. We evaluated whether the entomopathogenic fungi Beauveria bassiana and Metarhizium brunneum, applied to soybean seeds, could establish as endophytes in soybean and affect interactions with soybean aphid (Aphis glycines Matsumura). We found that M. brunneum (strain F52) increased populations of A. glycines on treated plants, but B. bassiana (strain GHA) had no effect. We were able to recover both fungi as endophytes in soybean, but B. bassiana was the more prevalent. Our work confirms that some entomopathogenic fungi can be endophytic in soybean, however, these fungi may have a negative effect on the plants by increasing susceptibility of soybean to A. glycines. We also used DNA sequence data to identify species of Metarhizium obtained from agricultural fields in Iowa. Phylogenetic analyses, based on DNA sequence data, for Metarhizium isolates from agricultural fields indicated that all isolates were Metarhizium robertsii, which is consistent with past studies indicating a cosmopolitan distribution and wide host range for this species.