Endophytic fungi are found in most, if not all, plant species on the planet. They colonise inner plant tissues without causing symptoms of disease, thus providing benefits to the host plant while a...

https://www.tandfonline.com/doi/pdf/10.1080/21501203.2021.1945699

Endophytic fungi: a tool for plant growth promotion and sustainable agriculture

Endophytic Metarhizium robertsii promotes maize growth, suppresses insect growth, and alters plant defense gene expression

Plants are immobile organisms that require roots to efficiently and cost-effectively exploit their habitat for water and nutrients. Plant root systems are dynamic structures capable of altering root branching, root angle, and root growth rates determining overall architecture. This plasticity involves belowground plant-root mediated synergies coupled through a continuum of environmental interactions and endogenous developmental processes facilitating plants to adapt to favorable or adverse soil conditions. Plant root branching is paramount to ensure adequate access to soil water and nutrients. Although substantial resources have been devoted toward this goal, significant knowledge gaps exist. In well-studied systems such as rice and maize, it has become evident that root branching plays a significant role in the acquisition of nutrients and other soil-based resources. In these crop species, specific root branching traits that confer enhanced nutrient acquisition are well-characterized and are already being incorporated into breeding populations. In contrast, the understanding of root branching in root and tuber crop productivity has lagged behind. In this review article, we highlight what is known about root branching in root and tuber crops (RTCs) and mark new research directions, such as the use novel phenotyping methods, examining the changes in root morphology and anatomy under nutrient stress, and germplasm screening with enhanced root architecture for more efficient nutrient capture. These directions will permit a better understanding of the interaction between root branching and nutrient acquisition in these globally important crop species.

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Root Branching and Nutrient Efficiency: Status and Way Forward in Root and Tuber Crops

Fungal entomopathogens,
 Beauveria bassiana
 (NATURALIS) and
 Metarhizium brunneum
 (BIPESCO5), can promote the growth of wheat following their endophytic establishment within plants through seed treatment. Similar to endophytic
 B. bassiana
 which has already been reported as a disease antagonist by several previous studies, the present study demonstrates that
 M. brunneum
 can suppress disease pathogens following plant colonization as well.
 An upsurge of research hints at the ability of entomopathogenic fungi, almost exclusively considered and used as insect pathogens, to endophytically colonize the internal tissues of a wide array of host plants and subsequently confer numerous benefits including enhancement of plant growth and suppression of disease pathogens. Such an ability has mainly been investigated for Beauveria bassiana. Fewer studies have demonstrated plant growth promotion by Metarhizium brunneum colonization, whereas no studies have reported on the potential of endophytic M. brunneum as a plant disease antagonist. The present study was, therefore, conducted to investigate whether seed treatment with B. bassiana (NATURALIS) and M. brunneum (BIPESCO5) could result in their endophytic establishment in wheat and promote plant growth. The study further examines the effect of the fungal strains as endophytes against Fusarium culmorum, one of the main causal agents of crown and root rot (CRR) in wheat. Both B. bassiana and M. brunneum were able to systemically colonize roots and shoots of wheat, and promote several plant growth parameters (shoot height, root length, and fresh root and shoot weights). Moreover, endophytic colonization of wheat with either fungal entomopathogen resulted in a significant reduction in disease incidence, development and severity. These results support the notion of the multiple ecological roles that could further be played by entomopathogenic fungi. Bearing such additional roles in mind while developing these fungi as microbial agents could improve the value of many commercially available mycoinsecticides.

Seed inoculation with endophytic fungal entomopathogens promotes plant growth and reduces crown and root rot (CRR) caused by Fusarium culmorum in wheat

Several ascomycetous insect-pathogenic fungi, including species in the genera Beauveria and Metarhizium, are plant root symbionts/endophytes and are termed as endophytic insect-pathogenic fungi (EIPF). The endophytic capability and insect pathogenicity of Metarhizium are coupled to provide an active method of insect-derived nitrogen transfer to plant hosts via fungal mycelia. In exchange for the insect-derived nitrogen, the plant provides photosynthate to the fungus. This symbiotic interaction offers other benefits to the plant-EIPF can improve plant growth, they are antagonistic to plant pathogens and herbivores and can enhance the plant tolerance to abiotic stresses. The mechanisms and underlying biochemical and genetic features of insect pathogenesis are generally well-established. However, there is a paucity of information regarding the underlying mechanisms in this plant-symbiotic association. Here we review five aspects of EIPF interactions with host plant roots: (i) rhizosphere colonization, (ii) signalling factors from the plant and EIPF, (iii) modulation of plant defence responses, (iv) nutrient exchange and (v) tripartite interactions with insects and other micro-organisms. The elucidation of these interactions is fundamental to understanding this symbiotic association for effective application of EIPF in an agricultural setting.

Root colonization by endophytic insect-pathogenic fungi.

Encapsulation of Metarhizium brunneum enhances endophytism in tomato plants

Endophytic Metarhizium brunneum mitigates nutrient deficits in potato and improves plant productivity and vitality

Cellulase enhances endophytism of encapsulated Metarhizium brunneum in potato plants.

Recent studies indicate the potential of endophytic entomopathogenic fungi to promote plant growth but little is known about the responses of root architecture to fungal endophytism. This study investigates potential adaptations of root architecture upon Metarhizium brunneum endophytism linked to improved plant growth and nutrition. Plants (Solanum tuberosum L.) were grown in the presence of M. brunneum applied either as non-formulated mycelium or as mycelium containing beads. After 35 days, fungal growth, root endophytism, plant biomass and nutrition as well as root attributes were determined. In response to endophytism promoted by bead application, plant P contents and biomass were significantly increased, while N contents and shoot allocation were also significantly increased in plants from the beads without mycelium group. Bead application resulted in a shift from fine to medium-sized roots and in an increase in the number of root forks, while root diameter, surface area and the number of root tips and crossings were independent of either bead or M. brunneum treatment. M. brunneum containing beads supported endophytism allowing for increases in plant P contents and biomass. However, root architecture was not strongly modulated by M. brunneum endophytism with N provision through bead application being more important than fungal P delivery.

Importance of phosphorus supply through endophytic Metarhizium brunneum for root:shoot allocation and root architecture in potato plants

Successful commercialization of microbial biocontrol agents, such as Metarhizium spp., is often constrained by poor drying survival and shelf life. Here, we hypothesized that culture age would influence endogenous arabitol, erythritol, mannitol and trehalose contents in M. brunneum mycelium and that elevated levels of these compounds would improve drying survival and shelf life of encapsulated mycelium coupled with enhanced fungal virulence against T. molitor larvae. We found that culture age significantly influenced endogenous arabitol and mannitol contents in mycelium with highest concentrations of 0.6 ± 0.2 and 2.1 ± 0.2 µg/mg after 72 h, respectively. Drying survival of encapsulated mycelium was independent of culture age and polyol content with 41.1 ± 4.4 to 55.0 ± 6.2%. Best shelf life was determined for biomass harvested after 72 h at all investigated storage temperatures with maximum values of 59.5 ± 3.3% at 5 °C followed by 54.5 ± 1.6% at 18 °C and 19.4 ± 1.3% at 25 °C after 6 months. Finally, high fungal virulence against T. molitor larvae of 83.3 ± 7.6 to 98.0 ± 1.8% was maintained during storage of encapsulated mycelium for 12 months with larval mortalities being independent of culture age and polyol content. In conclusion, our findings indicate beneficial effects of endogenous polyols in improving shelf life of encapsulated mycelium and this may spur the successful development of microbial biocontrol agents in the future.

https://link.springer.com/content/pdf/10.1007%2Fs11274-018-2492-x.pdf

Vivien Krell

Papers

Encapsulation of Metarhizium brunneum enhances endophytism in tomato plants

Endophytic Metarhizium brunneum mitigates nutrient deficits in potato and improves plant productivity and vitality

Cellulase enhances endophytism of encapsulated Metarhizium brunneum in potato plants.

Importance of phosphorus supply through endophytic Metarhizium brunneum for root:shoot allocation and root architecture in potato plants

Endogenous arabitol and mannitol improve shelf life of encapsulated Metarhizium brunneum.