Arbuscular mycorrhizal fungi (AMF) deliver important ecosystem services and play a key role for major soil and plant functions, including root health and plant nutrition, soil health and fertility, as well as preventing soil erosion and facilitating water infiltration. Importantly, they contribute to climate smart agriculture. Living collections of indigenous AMF have been developed by the authors since 1980 at: I) CIAT (International Center for Tropical Agriculture), Colombia, ii) IITA (International Institute of Tropical Agriculture), Benin/Nigeria (together with the University of Basel, UNIBAS), iii) at UNIBAS a tri-national collection from the countries surrounding Basel), iv) the Swiss Agroscope collection of AMF (SAF), into which the trinational collection was integrated. Recently another collection was initiated at the National University of San Martín in Peru. These collections contain ~350 AMF isolates, belonging to over 50 species, most of which have been screened for their beneficial effects on crop growth, nutrient uptake and soil health on various crops: e.g. cassava, beans, white yam, coffee, inka nut, soybean, wheat, strawberry, and leek. Some outstanding results from those screening activities will be presented, and the isolates that proved the most beneficial in terms of crop growth and soil health are highlighted. The special properties of some AMF species, their phylogeny, life cycle strategies and their protective effects against root pests and diseases (e.g. nematodes or pathogens) will also be presented and the drawbacks for their implementation in agriculture discussed. From experiments performed in the Tropics, isolates belonging to Rhizoglomus, Funneliformis, Sclerocystis, Entrophospora, Diversispora and Acaulospora, proved most effective, while species in the early ancestral clades, Archaeospora and Paraglomus, rarely showed a positive effect. In experiments performed in Europe, isolates of Funneliformis, Rhizoglomus, Entrophospora and Diversispora were among the most effective, while species from Archaeospora and Paraglomus were least effective on crop growth. However, there were species and genera within Glomeraceae, which also had no effect on plant growth, while others had short-term (few months) or long-term (several to multiple months) effects, but rarely both. For example, within the Glomeraceae and Entrophosporaceae, Rhizoglomus spp., Funneliformis mosseae and Entrophospora claroidea promote crop growth for a few months only, while Dominikia aurea and Septoglomus constrictum impact plant growth over several crop cycles. This may be linked to their life cycle and survival strategies. For the magnitude of effects on plant growth and for the greatest diversity of species having a positive impact on plant growth, Rhizoglomus stands out as the genus providing the most beneficial effects, from species such as R. intraradices, R. irregulare, R. clarum and R. manihotis, in addition to R. variabile and R. invermaium, which were only recently found to be highly beneficial for crops. Species from the ancestral AMF orders, however, have rarely been found to be beneficial (e.g. Archaeospora myriocarpa and Paraglomus occultum). There are only limited data for effects by species of Gigasporales, which is the youngest of the six AMF orders. Gigasporales appear to be most prevalent in warmer, subtropical and tropical climates, and where they have the most promising effect on plant growth, health and soil fertility, most probably in the long-term. Within our collections, ~100 AMF isolates that positively stimulate plant growth and/or improve plant health have been identified. Occasionally, negative but never strongly negative effects were observed, although negative effects have been reported elsewhere. Most isolates demonstrating beneficial effects belong to the Glomeraceae, which is opportune for their use in agricultural settings, as these tend to be easiest to propagate, and to scale up. Using combinations of AMF isolates/species also offers promise but knowledge on their combined effects needs first to be assessed, as some combinations can be antagonistic and their mutual benefits not necessarily additive. In conclusion, the living collections of AMF offer potentially colossal benefits to agriculture and beyond. This is particularly pertinent under the current sociopolitical climate with rising fertilizer and synthetic farming input costs, as well as the challenges that climate change presents, and the need to more efficiently use our water resources. The maintenance of these living reservoirs is therefore critical, but requires an equally colossal effort to keep them alive and available.
