Mass Production of Arbuscular Mycorrhizal Fungus Inoculum and Its Use for Enhancing Biomass Yield of Crops for Food, for In Situ Nano-Phyto-Mycorrhizo Remediation of Contaminated Soils and Water, and for Sustainable Bioenergy Production

Food and energy resources are gradually becoming scarce due to ever-increasing consumption and demand and the world faces crises. Resources like land, air, and water are increasingly becoming contaminated with heavy metal contaminants produced by wastages due to municipal, industrial, and mining activities by humans. There is an urgent need to address these problems by reclaiming the HM-contaminated soil and aquatic ecosystems for food and energy production. Various physicochemical remediation strategies are being developed and tested, but they are all expensive and applicable to small areas. During the past couple of decades, eco-friendly plant-based strategy, phytoremediation, is gaining popularity due to its economic and aesthetic values. But, it is very time-consuming and often hampered by the plant involved being slow-growing, producing contaminant-laded biomass with the added cost of safely disposing, and requiring the use of costly fertilizers. To overcome all these drawbacks, the process can be hastened by using plant growth-promoting soil microbiota, especially universal and ubiquitous arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR). However, AMF being obligate symbionts, and production of its mass-scale inoculum for field application is an obstacle. Various commercial AMF inoculants, mixed with PGPR, developed by in vitro and in vivo production methods using substrate-based and substrate-free (hydroponics and aeroponics) base systems, are available in the international market, but they were reported to produce mixed, variable, and inconsistent results. We developed in our laboratory using a substrate-free system, Ultrasonic Nebuliser Aeroponic System. Pre-inoculated with AMF propagule (isolated from the rhizospheres of plants grown in the HM-contaminated sites to be remediated) was grown in the aeroponic system to produce adequate adventitious roots with extensive extraradical mycelium network outside the root surface of the test plant used. The aeroponically grown mycorrhizal roots were then sheared, air-dried, and used as inoculum to test its infectivity and efficiency in the roots of the plants in the field, in competition with the indigenous and not efficient AMF propagules in the field soil, causing intensive mycorrhization of root cortices, uptaking contaminants into their aerial parts (phytoremediation) and producing high biomass for bioenergy production, that is, Nano-Mycorrhizo-PhytoRemediation.