Endophytes in commercial micropropagation - friend or foe?

Abstract

Medicinal and aromatic plants are superorganisms like all plant species- naturally colonized by bacteria, fungi and protists. 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. The use of endophytes in micropropagation can improve plant growth, yield, and health and induce tolerance to abiotic and biotic stress. 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 used commercially 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. Plantgrowth 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.