**6. Contribution of mycorrhizal fungi to agriculture**

The effect of AM fungi inoculation combined with appropriate agronomic measures on improving soil fertility, promoting plant growth, and increasing plant yield is greater than any single effect. For example, rotation, intercropping, or grass orchard inoculation of AM fungi are more obvious. At present some countries in the world are not rich in land resources, continuous cropping cultivation, especially the protection land contact for many years, resulting in soil fertility, soil quality, and ecological comprehensive service function decline, it is difficult to meet the needs of production. Therefore, it is worthy of systematic research and development to establish a new system of soil and seedling management dominated by mycorrhizal fungi inoculation to overcome continuous cropping obstacles under the combined cropping pattern of multiple crops mixed planting structure and rotation and intercropping. It is foreseeable that the implementation of AM fungi inoculation combined with appropriate agricultural measures will continue to develop and become an important emerging agricultural technology.

#### **6.1 Application of AMF technology in agriculture**

Most crops show some mycorrhizal dependence on AMF. AMF can promote crop uptake of soil nutrients, promote crop growth, improve crop yield, improve fertilizer use efficiency, and reduce fertilizer consumption, which is conducive to maintaining sustainable agricultural development. At present, there are research institutions and companies in the world that can produce AMF fungicides on a large scale [51].

In practical application, selecting crops with strong mycorrhizal dependence and high economic value to promote the application of mycorrhizal biotechnology has great ecological and economic benefits.

Many studies have shown that AMF inoculation can increase the yield of maize, wheat, soybean, and other major grain crops, improve crop nutritional status, and enhance crop resistance to drought, salinity, and other stresses [52, 53]. The commercial fungicide MYKEPROSG2 (Canada) was used to inoculated maize, and it was found that the P content of host plants could still be increased in the presence of indigenous AMF [54]. AMF combined with chemical fertilizer can improve the quality of rice and increase the contents of Fe and Zn in rice [55]. Ceballos inoculated cassava (Manihot esculenta), an important food crop in tropical regions, with *Rhizophagus irregularis*, which greatly increased its yield [56]. The effectiveness and economy of AMF inoculation could be taken into account when 2500 spores were inoculated per cassava.

#### **6.2 Application of AMF technology in horticulture**

Most horticultural crops can form symbiotic systems with AMF, such as Solanaceae, Onionaceae, most fruit trees, herbs, herbs, and ornamental flowers. Horticultural crops have high economic value and are used to nursery and container seedling, which provides convenient conditions for mycorrhizal plants at seedling stage. After mycorrhizal inoculation, it can shorten the nursery period of seedlings, improve the survival rate of transplanting, promote seedling growth, enhance disease resistance, ultimately improve product yield and quality, increase the economic added value of horticultural crops, and obtain greater benefits with less investment.

Under the premise of halving fertilizer application rate, Ziane (2020) inoculated tomatoes with commercial fungicide Symbivit, indigenous fungicide *Aspergillus moxicanus*, and *Septoglomus constrictum*, which could improve plant biomass and achieve the effect of 100% fertilizer application rate without inoculation [57]. The inoculation of horticultural crops such as fruit trees and vegetables can improve the yield and quality of fruits and vegetables. For example, the inoculation of *Glomus trufemii* on cucumber improved the quality of single fruit and the total yield per plant, while the contents of soluble protein and Vc in fruit were significantly increased [58]. AMF can also promote the formation of secondary metabolites and active substances in herb spices and medicinal plants, such as *Salvia japonica* inoculated with commercial bacteria and *Septoglomus viscosum*, the content and quality of essential oil in plants were significantly improved, and the proportion of taxol increased [59]. Xie (2018) found that the content of glycyrrhizic acid and liquiritin in roots of *Glycyrrhiza uralensis* increased significantly after inoculation with AMF [60]. Mycorrhizal plants have stronger adaptability under adverse conditions such as drought and salinity. The activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and guaiacol peroxidase (GPOX) in vivo are significantly increased, which can slow down the oxidative damage of plants and make plants have stronger resistance to water deficit [61, 62]. Selecting appropriate AMF for inoculation of plants can not only promote the absorption of phosphorus (P) by plants but also increase the contents of Zn, Cu, Mn, and other trace elements in plants [63, 64]. Therefore, mycorrhizal biotechnology can substantially reduce the use of fertilizers and pesticides, avoid pesticide residues in fruit and vegetable products, and improve the quality of fruits and vegetables.

In the international production of fruit trees and flowers, AMF has been widely used as biological protective agent, biological accelerator, and biological fertilizer.
