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Endophyte

Also known as
endophytic, endophytic microbe

An endophyte is a bacterium or fungus that lives inside a plant's tissues for at least part of its life without causing disease. Some endophytes benefit their host, for example by improving nutrient uptake, growth or tolerance to stress.

What is an endophyte?

The word endophyte means “inside the plant.” An endophyte is a microorganism, usually a bacterium or fungus, that lives within the tissues of a plant, in the roots, stems or leaves, for all or part of its life, without causing symptoms of disease. Virtually every plant studied carries endophytes.

Endophytes are defined by where they live, not by what they do. Many appear to have no measurable effect on the plant; some benefit it; and some organisms that live quietly inside one plant can cause disease in another or under different conditions. In agriculture, interest centers on endophytes that have been shown to help crops.

How endophytes enter and live in plants

Most bacterial endophytes enter through the roots, often at natural openings such as the points where lateral roots emerge, or through small wounds. From there, some remain in the root while others move into stems and leaves. Fungal endophytes may enter through roots or leaves, and some are passed down through seed. Inside the plant they live in the spaces between cells or in the water-conducting tissue.

Endophytes and root-zone microbes

The soil immediately around roots, the rhizosphere, hosts a dense microbial community that lives on and around the root surface. Endophytes go a step further and live inside the plant. The two groups overlap: many endophytes start out as rhizosphere microbes, and some beneficial bacteria, including some plant growth-promoting rhizobacteria, can live in both places. Living inside the plant shelters an organism from competition and changing soil conditions, which is one reason endophytes are of interest as crop inputs.

How beneficial endophytes can help crops

Research has identified several ways endophytes can benefit their hosts, varying by organism and crop:

  • Nutrient acquisition, including helping make phosphorus and other nutrients available, and in some cases contributing to biological nitrogen fixation.
  • Growth regulation, by producing or modifying plant hormones that influence root growth.
  • Stress tolerance, for example by lowering the stress hormone ethylene in roots under drought or salinity.
  • Plant protection, by competing with pathogens, producing antimicrobial compounds, or priming the plant’s own defenses.

A well-known example outside row crops is the fungal endophytes of some forage and turf grasses, which produce compounds that deter insects.

Endophytes as crop inputs

Endophytic products are applied as seed treatments, in furrow or through irrigation, so that the organisms can colonize the young root system. As with any microbial inoculant, results depend on the strain, on whether enough live organisms reach the root, and on field conditions.

Endophytes at Locus

Locus describes its Rhizolizer biologicals for row and specialty crops and its Terradigm turf product as endophytic, meaning the organisms are intended to establish inside the root system and support root development and nutrient use from early in the season.

Frequently asked questions

Both live in close association with roots. Mycorrhizae are fungi that form a specific partnership with roots, partly inside root cells and partly extending into the soil as a network of fine threads that gather nutrients. Endophyte is a broader term for any microorganism living inside plant tissue without causing disease.

Both. Bacterial and fungal endophytes are common, and a single plant usually hosts many of each.

By definition an endophyte does not cause disease while living in the plant, but the line is not fixed. Some microbes are harmless in one host or condition and pathogenic in another, which is why beneficial endophyte products rely on specific, characterized strains.

  • Rhizosphere

    The rhizosphere is the thin zone of soil immediately surrounding plant roots that is directly influenced by them. Roots release sugars, amino acids and other compounds there, which feed a dense, active community of microorganisms that affects nutrient availability and plant health.

  • Plant growth-promoting rhizobacteria PGPR

    Plant growth-promoting rhizobacteria (PGPR) are bacteria that live in the soil around roots, on root surfaces or inside roots and benefit plant growth, for example by making nutrients available, producing plant hormones or protecting against disease.

  • Mycorrhizae

    Mycorrhizae are symbiotic associations between certain soil fungi and plant roots. The fungi extend a network of fine threads into the soil that gathers water and nutrients, especially phosphorus, for the plant, and the plant supplies the fungi with sugars in return.

  • Microbial strain

    A microbial strain is a genetically distinct variant within a species of bacterium, fungus or other microorganism. Strains of the same species can differ markedly in traits that matter for agricultural products, such as how well they fix nitrogen, colonize roots or survive stress.

  • Agricultural biological

    An agricultural biological is a crop input derived from living organisms or natural materials, such as beneficial microorganisms, plant extracts or fermentation products, used to improve plant nutrition, growth, stress tolerance or protection from pests and disease.

Sources

  1. The hidden world within plants: ecological and evolutionary considerations for defining functioning of microbial endophytes, P. R. Hardoim et al., Microbiology and Molecular Biology Reviews, 2015
  2. Plant growth-promoting bacteria and endophytes, Peer-reviewed reviews