Bioaugmentation of Entomopathogenic Fungi for Sustainable Agriotes Larvae (Wireworms) Management in Maize

Abstract

Soil microorganisms influence biotic and abiotic stress tolerance of crops. Most interactions between plant symbiotic and non-symbiotic soil microorganisms and plants occur in the rhizosphere and are sustained through plant exudation/rhizodeposition. Bioaugmentation, i.e., the introduction or amplification of certain plant beneficial microbes (e.g., entomopathogenic fungi) into the rhizosphere, could contribute to controlling insect crop pests and replacing chemical, environmentally unfriendly insecticides. Wireworms, the soil-burrowing larval stages of click beetles (Coleoptera: Elateridae), are major pests of crops including maize, wheat and potatoes, worldwide. Alternative strategies for controlling wireworms are needed because several chemical pesticides used successfully in the past are being phased out because of their ecotoxicity. Therefore, virulence to Agriotes lineatus L. wireworms and plant beneficial traits of entomopathogenic fungi were investigated in a series of laboratory experiments. Tested taxa included environmentally retrieved Metarhizium brunneum Petch. (two strains), M. robertsii Bisch., Rehner & Humber (Hypocreales: Clavicipitaceae), and Beauveria brongniartii (Sacc.) Petch. and commercially formulated B. bassiana (Bals.-Criv.) Vuill. (Cordycipitaceae) and Bacillus thuringiensis Berliner 1915 var. kurstaki. In-house reared larvae were dipped in conidial suspension, and maize and wheat seeds were coated with fungal conidia. Metarhizium brunneum strains 1154 and 1868 significantly increased wireworm mortality. Fungi were significantly more often re-isolated from maize than wheat rhizoplanes in laboratory assays. The strains tested were rarely isolated as endophytes. Metarhizium brunneum strain 1154 stimulated wheat growth, while M. robertsii 1880 stimulated maize growth, whereas M. brunneum 1868 and others did not affect root or shoot length or plant biomass significantly in laboratory settings. Metarhizium brunneum strain 1868, re-isolated most often from maize rhizoplane, caused the highest wireworm mortality. It was further evaluated whether M. brunneum 1868 can protect maize varieties FeroXXY, LG 34.90 and Chapalu from wireworm damage and promote plant growth at field conditions. Plants of all three varieties stemming from seeds treated with conidia of M. brunneum 1868 showed significantly less wireworm damage 3 to 4 weeks after sowing (5

Testing Virulence of Different Species of Insect Associated Fungi against Yellow Mealworm (Coleoptera: Tenebrionidae) and Their Potential Growth Stimulation to Maize

“…The effects of coating maize seeds with Metarhizium are often beneficial. Razinger et al [44] reported a significant increase in fresh weight of maize by coating seeds with M. robertsii, but no effect on plant length, whereas colonized maize plants of Ahmad et al [1] were greater in length and shoot biomass. Kabaluk and Ericsson [56] treated maize seeds with Metarhizium anisopliae (Metschn.)…”

“…Metarhizium robertsii isolates (2698, 2700 and 2154) also significantly prolonged the emergence time. Razinger et al [44] and Kuzhuppillymyal-Prabhakarankutty et al [45] also reported a lower germination rate of maize seed; this could be a consequence of the method by which the conidia were applied to the seeds, namely by using carboxymethyl cellulose or methylcellulose. In our case, the maize seeds were soaked in a suspension of fungal conidia using only 0.1% Tween 80 to overcome the difficulties with the hydrophobic properties of the conidia of the fungal species under study and to allow adequate adhesion of the conidia to the maize kernels.…”

“…The obtained suspensions were collected into sterile 50 mL Falcon tubes. Haemocytometer (Bürker-Türk, BRAND GMBH + CO. KG, Wertheim, Germany) counting was used to adjust obtained suspensions to a concentration of 1 × 10 8 conidia ml −1 [44]. The viability of conidia was determined by counting germinated conidia after 24 h of incubation of the diluted suspension sample.…”

A Holistic Approach for Enhancing the Efficacy of Soil Microbial Inoculants in Agriculture

“…The multifunctional use of bio-inocula [101][102][103][104] could be exploited to support the development, marketing, and application of microbial-based products. However, the current legal framework in the European Union, as well as in other countries, on the production and marketing of microbial-based products poses serious challenges to exploit the multifunctionality of beneficial microbes.…”

Resporulation of Calcium Alginate Encapsulated Metarhizium anisopliae on Metham®-Fumigated Soil and Infectivity on Larvae of Tenebrio molitor

“…For this reason, fungal adaptation, especially in agroecosystems, has been viewed as a crucial attribute that needs to be evaluated for any entomopathogenic fungal (EPF) candidates before their field application. Some Metarhizium species, for example, M. anisopliae , M. brunneum and M. robertsii, demonstrate a strong association in the soil environment in terms of rhizosphere colonization [ 19 , 20 ] and endophytic establishment in plant roots, for example, in cassava [ 21 ] and in tomato [ 22 ]. Fungal–plant interactions, such as endophytism or rhizosphere competence, can confer crop protection against root herbivores [ 20 ] and even result in the suppression of root herbivores by altering the gene expression of the host plant [ 23 ].…”