Strategies to improve mycorrhizal inoculum quality for field application

Agriculture ensures the provision of food together with several other ecosystem services. However, modern agriculture, based on a wide use of chemical products, turned out to be not sustainable in the long run. Therefore, new production strategies are needed in order to maintain high crop production with a reduced use of chemical inputs. Arbuscular mycorrhizal fungi are well-known class of microorganism able to colonize the majority of plant species. These fungi provide a series of benefits to the host plant and for these reasons, implementation of their use in agriculture have been suggested as a valid strategy to reduce the need for chemicals in the field. However, their application in practical condition is still limited by a series of factors, among them, the high concentration of phosphate in soil deriving from fertilization. In order to exploit the benefits that arbuscular mycorrhizal fungi may provide to crop plants, the development of a newly formulated inocula, adapted to the environment present in the field, are needed and represent the subject of the present work. Therefore, different strategies have been proposed and tested for the development of suitable inocula, one directed to the fungus and one to the plant. In the first approach, the ability of the fungi to adjust to hostile environment has been exploited. The second strategy assumed that plant physiology is the main driver of mycorrhizal symbiosis. Here, use of inducer molecules, able to modulate plant metabolism, have been proposed and tested, in vitro, and in vivo, both in greenhouse test and in the field. The results indicated acclimatisation as a promising technique to cope with phosphate stress in practical conditions. However, the tests underline that phosphate cannot be considered as the only limiting factor occurring in the field that limit the possibility to exploit the symbiosis. Based on this consideration, strategies are proposed to develop new inocula for the future.