**4. Perspectives**

specific plant–AMF combinations, as mentioned in the previous section, in order not to reduce AMF propagation and diminish plant dependency on mycorrhization after inoculation. Other edaphic factors, such as pH, salinity, soil temperature, moisture and soil aeration, should also be controlled to optimize AMF inoculation. Since the inadequacy of the nutrient composition dramatically affects AMF development, conventional soil analyses should be performed on the formulated inoculum, in independent official laboratories, as a quality control step. This way, the manufacturer will be provided with a certificate that guarantees the customers the validity of the data reported on the label and, therefore, enhances the quality of the inoculum. During experimental tests on the beneficial effects of inoculants, researchers often adopt an important practice in order to be able to differentiate between the effects of the inoculum carrier and the AMF portion, i.e. the use of a sterilized inoculum as a control, the so-called "mock" inoculum [145]. This practice of including a non-inoculated and a "mock" inoculated control should be considered by end-users who are willing to assess the eventual beneficial effect of

A few alternatives to the pot-culture method are available, regarding inoculum production and formulation. Other soilless culture systems, such as aeroponics and hydroponics, enable the production of pure clean spores and maximize growing conditions for the host plant [146]. Aeroponic inoculum production has long been scientifically validated [147,148], and could soon reach massive commercialization levels. Root-organ monoxenic culture is another method that allows the successful large-scale propagation of AMF which can be used directly as an inoculum. Unfortunately, the protocol for this method of propagation is not easily adjustable to all AMF strains. So far, several dozens of AMF species and strains have been propagated in vitro with the right synthetic growth medium and growth conditions. This type of culture consists of AMF inoculated excised roots (often *Daucus carota* L.) that have acquired the ability to uncontrollably proliferate, without the epigeous portion, after transformation with an *Agrobacterium rhizogenes* Conn. strain. This method of propagation does not require high specialization, and facilitates the control of AMF strain purity. As mentioned before, it is suitable for large-scale production, as a massive number of spores (several thousand), mycelium and colonized roots [149] can be obtained from one Petri dish in just 4 months, and from the consecutive subcultures [150]. AMF propagated with this technique have been shown to successfully re-colonize plant roots [151,152]. A possible further advantage of the AMF inoculum production process could be the use of bioreactors with liquid transformed rootorgan cultures aimed at the large-scale propagation of AMF [153]. These tools may become suitable for commercialization in the near future and will lead to reduced labor and enhanced automation. However, as the AMF are produced in association with transformed roots, the product will only be intended for research use and may not be used for open-field inoculation.

The final product could become available on the market as a powder or granular substrate made from mixed inert-like materials, such as peat, compost, vermiculite, perlite, quartz sand, micronized zeolite and expanded clay, where colonized root fragments (1-5 mm long), spores and hyphal networks are uniformly distributed. Liquid inocula, dedicated to horticultural use, obtained from a hydroponic culture, or from a spore/mycelium suspension in a liquid carrier, represent a possible alternative final product [154]. As a final step before commercialization,

AMF inoculation.

176 Biodiversity - The Dynamic Balance of the Planet

Future research in this field will have to concern the formulation of AMF isolate collections, with comprehensive information on host-preference, edaphic and climatic adaptation, and stress and disturbance tolerance. This will help manufacturers address their product towards different uses, including agricultural use, as well as new fields of application, such as the green architecture of urban sites [159]. At the same time, farmers will have to begin asking for assistance from experts in the field when introducing AMF to their cropping systems. Scientists should also carry out large-scale multi-location field trials, and conduct cost-benefit analyses, in order to increase awareness among the end-users of AMF inocula.

By 2050, global agriculture will have the task of doubling food production in order to feed the world [160]. At the same time, dependence on inorganic fertilizers and pesticides must be reduced. For these reasons, significant advances in AMF research are needed to allow their stable use in agriculture. Their application and synergistic combination with other functionally efficient microbial consortia that include PGPR (Plant Growth Promoting Rhizobacteria), saprophytic fungi and other helper microorganisms [161], will help farmers develop a more sustainable cropping system.
