## 2 Endophytes-Current State of the Art
### Possibilities of Using Endophytes in Agriculture-Bioproducts and Strains Used in Biofertilizers  
By 2050, the global population is estimated to grow to 9.7 billion [148]. This will be associated with an increased demand for agricultural products, making it a priority to find solutions to increase the production efficiency of particularly important crops such as wheat, rice, maize and sugar beet [12]. In addition, unsustainable agricultural systems, a decreasing area for cultivation, climate change, a trend of increasing soil salinity and poor land management practices have led to an enhanced use of chemical fertilizers, pesticides and herbicides in agriculture, resulting in groundwater pollution, eutrophication, greenhouse gas production, soil nutrient imbalance and loss of soil microbial diversity [149; 150; 151; 152]. It is therefore necessary and justified to disseminate more sustainable and environmentally friendly agricultural production techniques that ensure food security. One such method is the use of endophytic organisms [153]. This is an ecological alternative to conventional agricultural practices as it relies less on the use of chemicals. What is more, endophytic bacteria and fungi can provide a wide range of benefits, from plant growth stimulation to plant protection against stress factors [154]. In recent years, the use of bioproducts based on microorganisms, including endophytic microorganisms, has become increasingly popular in agriculture [148; 154]. Bioproducts used in agriculture containing endophytic bacteria and fungi can include bioproparations, biofertilizers, biospecicides, biostimulants, vaccines and biocontrol agents [148; 155]. Biopreparations are substances containing living organisms or suitably prepared products of their metabolism [154; 155; 156]. Considering the composition, we distinguish between bacterial, fungal, bacterial-fungal, enzymatic and bacterial/fungal-enzymatic biopreparations [158]. Biopreparations are mainly dedicated to the inhibition of pathogenic fungi and bacteria [159; 160]. Numerous researchers claim that applying biopreparations to plant residues not only stimulates the mineralization process, but also accelerates the release of nutrients [161; 162]. Microorganisms often used as components of biopreparations are fungi of the genus _Trichodema_[162; 163]. They produce compounds that inhibit pathogen development and mycoparasitism. Moreover, they induce systemic immunity and stimulate plant growth [161]. They are also known for their very rapid growth and compete with parasitic fungal species such as _Fusarium_ sp. [161]. _Trichodema_ sp. is characterized by its ability to produce enzymes that efficiently decompose dead organic matter and thus contribute to improving the physical and chemical properties of the soil [162]. One of the best ways to increase or maintain the current rate of food production while ensuring environmental stability is to use biofertilizers [76; 150]. The main difference between biopreparations and biofertilizers concerns their composition. Biofertilizers contain organic matter and one or more organic active compounds in addition to selected microorganisms [156]. They enable microorganisms to adapt to new conditions, increase their activity and stimulate growth and development of crop plants [156]. Atmosphericnitrogen-fixing endophytes are commonly used in biofertilizers [57; 153]. Replacing chemical nitrogen fertilizers with biofertilizers is an efficient and environmentally friendly solution [150; 164; 165]. Due to their greater ecological benefits, direct contact with the plant, and delivery of nitrogen directly to the host, endophytic microorganisms are more often used as components of biological fertilizers compared to rhizospheric or epiphytic microorganisms [150; 166]. Endophytes commonly used in biofertilizers include bacteria from the genera _Azospirillum_, _Acetobacter_, _Azodotobacter_, _Pseudomonas_ and _Bacillus_[10].