Commercial use of endophytes in micropropagation

Micropropagated plants are facing different challenges under in vitro and ex vitro conditions: mixotrophic growth under low light conditions on artificial nutrient media, poor gas exchange in small vessels, abiotic stress, bad rooting, transplanting stress, low survival rate during acclimatization in greenhouse. Plants are superorganisms NDASH naturally colonized by myriads of bacteria, fungi and protists. Microbial endophytes are the dominant group of colonizers. Endophytes' behaviour can range from mutualism to antagonism and the use of endophytes in micropropagation can improve plant growth, yield, health and induce tolerance to abiotic and biotic stress. Micropropagated plants often harbor differences in their microbiome compared to plants conventionally grown and there is the risk of beneficial microbes being eliminated in micropropagation systems. A tool for the use of competent endophytes in micropropagation under in vitro and ex vitro conditions is “biotization” of plantlets with useful bacterial and fungal inocula. Fungal inocula, which are commercially used, are e.g., arbuscular mycorrhizal fungi in form of spores and extraradical mycelium on different carrier materials like expanded clay, vermiculite, sand or peat. Furthermore, representatives of the root fungal genus Trichoderma are applied as spores formulated in powder. Plant-growth promoting rhizobacteria of the important genera Bacillus, Pseudomonas, Azospirillum and Azotobacter in form of lyophilised endospores/bacterial cells in powder or liquid formulation are also available on the market. Inocula can be used as biofertilizers or biocontrol agents by dipping of microcuttings in bacterial suspensions or mixing of inocula with potting soils.