## 2 Endophytes-Current State of the Art
### Endophytes as Inhabitants of Agricultural Plants
#### 2.2.5 Endophytes of the Most Common Crops  
Cereal products are the basis of human nutrition. They provide the body with essential nutrients in amounts that meet its daily requirements [92]. Currently, global food production is dominated by the cultivation of three crops: maize, wheat and rice [92]. In the EU, wheat production is by far the most important, in terms of area, volume and revenue. This is due, among other reasons, to the fact that it is better adapted than other cereals to grow under suboptimal conditions [93]. Maize (_Zea mays_ L.) is grown on all continents except Antarctica, and its global importance extends to agriculture, the food industry and biofuels [94]. Global maize cultivation is rapidly growing, driven by increasing demand for food, feed, biofuels and industrial products. Major maize producers such as the US, China, Brazil and Argentina play a key role in the global trade and development of the sector [94]. Various groups of endophytes can be found in maize that affect its health and yield [91]. [PERSON] [95] reported that bacteria of the maize seed are dominated by Proteobacteria, Actinobacteria and Firmicutes, with the majority of fungi placed in the Ascomycota phylum. Among endophytic bacteria, the following are common for maize [96]: _Azospirillum_ spp. ; these nitrogenous bacteria support maize by improving N assimilation. _Rhizobium_ spp. and _Pseudomonas_ spp. can promote plant growth and protection against pathogens [91]. Various species of _Bacillus_, _Paenibacillus_, _Sphingomonas_, _Staphylococcus_, _Enterococcus_, _Pantoea_ and _Pseudomonas_ were found in maize tissues as well [96; 97]. Also, some of the most common fungal endophytes in maize were identified [96]: _Fusarium_ spp.--although some species are pathogenic, others can act as endophytes, supporting the plant against disease; _Aspergillus_ spp.--can promote plant growth and improve stress resistance, and _Penicillium_ spp.--often found in maize tissues, can promote plant health. Fungal endophytes isolated from maize seeds also include representatives of _Chuetomium cochlides_, _Chatomium subaffine_, _Chatosporium cladosporioides_, _Alternaria alternata_ and _Rhizopus oryzae_[98]. Seed endophytes are found to promote maize growth, which is usually expressed by increasing the size of roots, shoots and leaves [96; 98]. Other identified benefits include better germination [98], drought tolerance [99] and ion uptake [100]. Studies on endophytes in maize are still in progress, and their full potential as plant growth-promoting agents and disease protection are promising research areas. Also wheat (i.e., Triticum _aestiuum_ L., _T. durum_ L.) cultivation is one of the key crops worldwide, as wheat is one of the most important grains and a primary source of food for billions of people [101]. China and India are the world's largest wheat producers. However, wheat is a primary source of income for farmers and is a key export commodity for many countries. [PERSON] et al. [102] isolated bacterial endophytes from grains of emmer wheat _T. turgidum_ subsp. _dicocecum_ and identified the genera _Staphylococcus_, _Pantoea_, _Sphingobium_, _Bacillus_, _Kosakonia_ and _Microococcus_ as common endophytes. What is more, the indole-related compounds (auxins) that were produced by the endophytic _Pantoea_ spp. and _Bacillus_ spp. isolated from Oksamyt myronivs'kyi and Holikovs'ka grains may be regarded as one of the determinants of the wheat yield and its nutritional characteristics [102]. A large number of endophytic bacteria belonging to _Achromobacter_, _Acinetobacter_, _Arthobacter_, _Chitinophaga_, _Enterobacter_, _Erwinia_, _Flavobacterium_, _Klebsiella_, _Leifsonia_, _Microbispora_, _Microoccus_, _Micromosoma_, _Mycobacterium_, _Paenibacillus_, _Pseudomonas_, _Roseomonas_, _Staphylococcus_, _Streptomyces_ and _Xanthomonas_ genera have been isolated and identified from wheat [27; 103].