Systemic Colonization by Metarhizium robertsii Enhances Cover Crop Growth

Abstract

Fungi in the genus Metarhizium (Hypocreales: Clavicipitaceae) are insect pathogens that can establish as endophytes and can benefit their host plant. In field experiments, we observed a positive correlation between the prevalence of M. robertsii and legume cover crops, and a negative relationship with brassicaceous cover crops and with increasing proportion of cereal rye in mixtures. Here, we report the effects of endophytic M. robertsii on three cover crop species under greenhouse conditions. We inoculated seeds of Austrian winter pea (Pisum sativum L., AWP), cereal rye (Secale cereale L.), and winter canola (Brassica napus L.) with conidia of M. robertsii to assess the effects of endophytic colonization on cover crop growth. We recovered M. robertsii from 59%, 46%, and 39% of seed-inoculated AWP, cereal rye, and canola plants, respectively. Endophytic M. robertsii significantly increased height and above-ground biomass of AWP and cereal rye but did not affect chlorophyll content of any of the cover crop species. Among inoculated plants from which we recovered M. robertsii, above-ground biomass of AWP was positively correlated with the proportion of colonized root but not leaf tissue sections. Our results suggest that winter cover crops may help to conserve Metarhizium spp. in annual cropping systems.

Endophytic Metarhizium robertsii suppresses the phytopathogen, Cochliobolus heterostrophus and modulates maize defenses

“…These results are consistent with studies that report systemic colonization of diverse plant species by Metarhizium spp. [ 4 , 7 , 15 , 34 , 38 , 77 – 80 ].…”

“…Consistent with previous studies, maize plants grown from M . robertsii- treated seed had greater height and above-ground biomass compared to the non-inoculated control when the experiment was terminated [ 4 , 7 ]. In our study, there was no difference in height and above-ground biomass of maize in response to C .…”

“…naturally associate with the roots of grasses, shrubs, herbs, and trees under field conditions [ 30 , 31 ]. Experimentally, multiple species of Metarhizium colonize the roots of many plant species, including switchgrass, haricot bean, wheat, and soybean and promote plant growth [ 4 , 7 , 16 , 32 – 36 ]. For example, plant growth promotion has been observed for multiple species of Metarhizium spp.…”

“…For example, plant growth promotion has been observed for multiple species of Metarhizium spp. in tomato [ 34 ], maize [ 4 , 7 , 37 , 38 ], soybean [ 39 ], peanut [ 40 ], potato [ 41 ], cassava [ 35 ], sweet pepper [ 42 ], switchgrass and haricot beans [ 36 ].…”

Observations on the Relationships between Endophytic Metarhizium robertsii, Spodoptera frugiperda (Lepidoptera: Noctuidae), and Maize

“…At the end of the infection cycle, mycelium forms, and can exit the cadaver and produce conidia or colonize plant roots and transfer N to plants in exchange for C [15]. Entomopathogenic fungi, such as those in the genus Metarhizium Sorokīn (Hypocreales: Clavicipitaceae), have been used as microbial control agents for pest arthropods, including several species of Noctuidae [16][17][18][19]. Susceptibility of FAW larvae and adults to direct application of M. anisopliae has been demonstrated in laboratory assays [20][21][22].…”