Production of Microsclerotia From Entomopathogenic Fungi and Use in Maize Seed Coating as Delivery for Biocontrol Against Fusarium graminearum

Abstract

The commercial use of the entomopathogenic fungi Metarhizium spp. in biopesticides has gained more interest since the discovery that several species of this genus are able to colonize roots. In general, commercial products with Metarhizium are formulated based on conidia for insect pest control. The process of mass production, harvesting, and formulation of infective conidia can be detrimental for conidial viability. Entomopathogenic fungi such as Metarhizium spp. are able to produce high concentrations of resistant structures, known as microsclerotia, when grown in liquid media. Microsclerotia are desiccation tolerant, with excellent storage stability, and are capable of producing high quantities of infective conidia after rehydration. The aim of this study was to evaluate microsclerotia production by different isolates of Metarhizium spp. and determine the effect of microsclerotia coated onto maize seeds on plant growth in the presence of soil-borne pathogen Fusarium graminearum. On average, ~1 × 105 microsclerotia/mL were produced by selected isolates of M. anisopliae (A1080 and F672) and Metarhizium robertsii (F447). Microsclerotia were formulated as granules with diatomaceous earth and used for seed coating, after which propagules produced around 5 × 106 CFU/g of seeds. In the presence of the plant pathogen, maize plants grown from untreated seeds had the lowest growth, while plants treated with the Metarhizium microsclerotia had significantly greater growth than the control plants. Hyphae were observed growing on and in root tissues in all the Metarhizium spp. treatments but not in samples from control plants. Metarhizium hyphal penetration points' on roots were observed 1 month after sowing, indicating the fungi were colonizing roots as endophytes. The results obtained indicate that microsclerotia can be coated onto seeds, providing plant protection against soil plant pathogens and a method to establish Metarhizium in the ecto- and endo-rhizosphere of maize roots, allowing the persistence of this biocontrol agent.

Characterization of a new strain ofMetarhizium novozealandicumwith potential to be developed as a biopesticide

“…MS formation is artificially induced in entomopathogenic fungi and yield varies with the carbon concentration as well as the C:N ratio of liquid media (Jaronski and Jackson 2012 ). The yield obtained in the present work (10 3 MS/mL) was similar to those reported by Rivas-Franco et al ( 2020 ) for the isolate F99 of M. novozealandicum with ∼1 × 10 3 MS/mL and those reported for other species from the same genera such as M. anisopliae, M. robertsii and M. acridum , which reached maximum yields between 7.0 × 10 3 and 1.1 × 10 4 MS/mL (Mascarin et al 2014 ). Similar yields were also reported for the entomopathogenic fungi B. brongniartii and B. bassiana with 1.1 × 10 3 and 3.8 x 10 3 MS/mL, respectively (Villamizar et al 2018 ).…”

“…M. novozealandicumwas also pathogenic to grass grub (C. giveni) reaching 69.2% efficacy at 21 days post challenge, similar to the level of control reported by Glare (1994), where 60% mortality caused by M. anisopliaeby day 35 after inoculation was observed. Rivas-Franco et al (2019) also reported similar mortalities, with values up to 67% when using M. anisopliae and up to 55% when using M. novozealandicumas a seed coating on maize seeds. The isolate AgR-F177 was demonstrated to be pathogenic against DBM but the efficacy only reached 45.7%, suggesting low virulence against this insect when compared with other fungal species such as Beauveria bassiana, Metarhizium rileyi and Isaria sinclairiithat can reach between 80% to 100% mortality (Duarte et al 2016).…”

“Ectomosphere”: Insects and Microorganism Interactions

“…Their endophytic behaviour allows them to colonise plant-derived substrates, affecting plant-volatile emissions during insect infestations [ 102 ]. Plant-derived substrates, such as rice grains, can be used for mass production and formulation of EFs [ 103 , 104 ].…”

Functional and Quality Assessment of a Spore Harvester for Entomopathogenic Fungi for Biopesticide Production

“…These fungi also produce resting structures known as sclerotia, which can help them survive in adverse environmental conditions. The colony morphology of these fungi can vary depending on the growth conditions [28,29].…”