**4. Conclusion**

the protection to the host plants against drought stress. Glutathione and ascorbate have a significant effect in conferring the protection and maintaining metabolic function of plants in

AMF are known to have an efficacious and sustainable mechanism. With this mechanism, tolerance to drought is enhanced in vegetables [167, 168]. AMF cause changes in the roots of plants, especially in length, density, diameter, and number of lateral roots [169]. Improved root structure in mycorrhizae plants allows the extraradical hyphae to extend beyond depletion zones of plant rhizosphere, which makes the water and low-mobile nutrient intake (P,

The AM symbiosis effectiveness in improving drought tolerance was also investigated in vegetables. Open-field tomato (*Solanum lycopersicum* L.) inoculated with AMF (*R. intraradices*) influenced the agronomical and physiological responses of exposure in different drought intensities [171]. Compared to non-inoculated ones, the fruit yield of inoculated plants in severe-moderate-mild drought stresses was high at a statistically significant level by 25, 23, and 16%, respectively. It was reported in this study that high crop performance in inoculated plants was associated with better nutritional status (higher N and P) in connection with the maintenance of leaf water status. Ikiz et al. [172] confirmed this effect on tomato. They showed that the colonization of processing tomato "Regal 87-5" plants by *F. mosseae* and *G. versiforme* might increase marketable yield by 20% and 32%, respectively, when compared with those of non-inoculated plants under mild-heavy drought stress. Greenhouse melon (*Cucumis melo* L. "Zhongmi 3") plants (inoculated with three *Glomus* species: *G. versiforme* and *R. intraradices* and, especially, *F. mosseae*) showed higher tolerance to drought stress than non-inoculated plants. This situation was determined in plant heights, root lengths, biomass production, and net photosynthetic rates [173]. They claimed that the increase in drought tolerance and better crop performance might be associated with the antioxidant enzyme production (SOD, POD, and CAT) and the soluble sugar accumulation by AM symbiosis. Lucy et al. [174] examined the mechanisms which affected the relief of drought by a mixture of *Glomus* spp. from Mexico ZAC-19 (*G. albidium*, *G. claroides*, and *G. diaphanum*) in Chile ancho pepper (*C. annuum* L. San Luis). They reported that ZAC-19 had the potential to be incorporated into Chile pepper transplant systems to relieve the harmful effect of drought in open-field production in Mexico, which was shown by high root-to-shoot rate and leaf water potential. In a similar manner, in [175] it was reported that drought enhanced bigger extraradical hyphae development of *G. deserticola* in bell pepper, and as a result, a high water intake, when compared to non-mycorrhizae plants. It was also reported that AMF symbiosis enhanced lettuce (*Lactuca sativa* L. "Romana") tolerance to drought and recovery. This enhancement was achieved via the modification of the plant physiology and the expression of plants genes [176, 177]. Lettuce, which was inoculated with the AMF *R. intraradices*, gave high root hydraulic conductivity and low transpiration in drought, when it was compared with non-inoculated plants. Authors [178, 179] also emphasized that the plants inoculated with AMF could regulate their abscisic acid (ABA) concentrations in a better and quicker manner than non-inoculated plants, which allows a better balance between leaf transpiration-root water movement in drought stress and recovery [180, 181]. It was reported that inoculation with AMF enhanced WUE in watermelon [182], which shows that AMF improved water intake and resulted in the host plant making

water deficit conditions.

Zn, and Cu) more efficiently under water stress [170].

78 Physical Methods for Stimulation of Plant and Mushroom Development

Today, the utilization of natural resources in agriculture comes to the forefront because of improving environmental awareness. The evaluation of the use of natural resources, such as mycorrhiza and a cleaner environment, is important both for economic reasons. Resources are often used as a source of plant nutrition in hydroponics. Given the chemical, the use of mycorrhiza in agriculture is very important in soil. Particularly with the use of mycorrhiza, the use of chemical fertilizers especially consisting phosphorus, can be reduced. As a conclusion, mycorrhizae are important for the growth of agricultural crops as well as healthy ecosystem functions. Many benefits of mycorrhizal symbiosis can be enhanced by changing agricultural practices which may decrease colonization and mycorrhizal abundance [194].

Hydraheaded stress caused by biotic and abiotic reasons is threatening modern agriculture. Several stress types explained in this chapter emphasize ethylene biosynthesis, which prevents plant growth by some tools at molecular level. In this chapter, for the purpose of regulating the plant ethylene, application of PGPR with ACC deaminase is crucial. Several roles of PGPR in saline conditions, in drought, waterlogging, biocontrol, temperature and nutritional stresses and in cut-flower industry and nodulation in legumes were not investigated in detail by researchers. In commercial terms, applying PGPR with ACC deaminase in agriculture may be useful. It may also be an important progress to obtain sustainable crop production and conservation. Because of several drawbacks, genetic modification of plant species is not probable (for example, proprietary rights, trade agreements among countries for genetically modified (GM) crops, and due to the limitations in DNA recombinant technology in some areas in the world). Because of all these reasons, using PGPR with ACC deaminase activity and similar innovations may be a cost-effective and environment-friendly way for sustainable agriculture.

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