Water deficit is one of the most severe abiotic stresses threatening crop growth and production on the globe. Water stress causes a series of morphological, biochemical, physiological, and molecular alterations that negatively influence plant productivity. However, in nature, plants are often associated with microbes that can modulate plant responses to water scarcity. Among beneficial microbes, arbuscular mycorrhizal fungi (AMF) are one of the most widespread symbiotic fungi colonizing the majority of agricultural plants. Besides an enhancement in plant nutrition, AMF have been reported to improve plant performance under water restrictions. In this chapter, we emphasize the benefits of AMF inoculation to crop production under water deficit based on related laboratory and field experiments. Variable outcomes and challenges of AMF application are also discussed for practical use in crop production under water scarcity.

As a result of climate change, drought and heat significantly reduced plant growth. Therefore, this study aims to explore and provide more insight into the effect of different arbuscular mycorrhizal fungi (AMF) strains (Rhizophagus irregularis, Funneliformis mosseae, and Funneliformis coronatum) on tomato plant tolerance against combined drought and heat stress, as well as combined drought and heat shock. A pot experiment was performed under controlled conditions in a growth chamber at 26/20 °C with a 16/8 h photoperiod. After six weeks of growth, one-third of plants were put in non-stress conditions, while another one-third were subjected to combined drought and heat stress (40% field capacity for two weeks and 38 °C/16 h and 30 °C/8 h for 5 days). The rest of the plants were exposed to combined drought and heat shock (40% of field capacity for two weeks and 45 °C for 6 h at the end of the drought period). All data were evaluated by one- and two-way analysis of variance (ANOVA). Means were compared by Duncan’s post hoc test at p < 0.05. The obtained results showed that combined drought and heat stresses had no significant impact on root colonization. Furthermore, stressed AMF plants exhibited a decrease in hydrogen peroxide and malondialdehyde content in the cells and showed changes in defense enzyme activities (peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), and glutathione S-transferase (GST)) in leaves as well as in roots compared with their relative non-mycorrhizal plants.

In this study, we report the interaction between an arbuscular mycorrhizal fungus, Septoglomus constrictum, and tomato plants under heat stress. For the first time, this interaction was studied by Illumina RNA-seq, followed by a comprehensive bioinformatic analysis that investigated root and leaf tissue samples. The genome-wide transcriptional profiling displayed fewer transcriptomic changes in the root under heat-stress conditions caused by S. constrictum. The top 50 DEGs suggested significant changes in the expression of genes encoding heat-shock proteins, transporter proteins, and genes of phytohormone metabolism involving jasmonic acid signalling. S. constrictum induced the upregulation of genes associated with pathways such as ‘drought-responsive’ and the ‘development of root hair’ in the root, as well as ‘glycolipid desaturation’, ‘intracellular auxin transport’, and ‘ethylene biosynthesis’ in the leaf. The pathways ‘biotin biosynthesis’ and ‘threonine degradation’ were found in both investigated tissue types. Expression analysis of transcription factors showed 2 and 11 upregulated transcription factors in heat-stressed root and leaf tissues, respectively. However, we did not find shared transcription factors. Heat-stressed arbuscular mycorrhizal plants suffered less oxidative stress when exposed to high temperatures. Colorimetric tests demonstrated less accumulation of H₂O₂ and MDA in heat-stressed mycorrhizal plants. This phenomenon was accompanied by the higher expression of six stress genes that encode peroxidases, glutathione S-transferase and ubiquitin carboxyl-terminal hydrolase in roots and leaves. Our findings provide a new perspective on elucidating the functional metabolic processes of tomato plants under mycorrhizal-heat stressed conditions.

The association between terrestrial plants and arbuscular mycorrhizal (AM) fungi is one of the most common and widespread mutualistic plant-fungi interaction. AM fungi are of beneficial effects on the water and nutrient uptake of plants and increase plant defense mechanisms to alleviate different stresses. The aim of this study was to determine the level of polyphenol oxidase (PPO), guaiacol peroxidase (POX) and glutathione S-transferase (GST) enzyme activities and to track the expression of glutathione S-transferase (GST) gene in plant-arbuscular mycorrhizal system under temperature- and mechanical stress conditions. Our results suggest that induced tolerance of mycorrhizal sunflower to high temperature may be attributed to the induction of GST, POX and PPO enzyme activities as well as to the elevated expression of GST. However, the degree of tolerance of the plant is significantly influenced by the age which is probably justified by the energy considerations.

The protective role of arbuscular mycorrhizal fungi (AMF) against the phytopathogen Clavibacter michiganensis subsp. michiganensis (Cmm) was examined in tomato plants. Seven different AMF isolates were used to determine which ones were able to induce effectively resistance against Cmm. Stems of seven-week tomato plants were infected with Cmm, then a disease severity index (DSI) was determined during the next three weeks. In addition to different responses to mycorrhizal inoculation, three levels of responses to the bacterial disease were recognized in treatments. Plants inoculated with Rhizophagus irregularis (Ri) showed both the highest colonization and the highest induced resistance to Cmm while the effect of Funneliformis mosseae, Gigaspora margarita and Claroideoglomus claroideum on mycorrhizal colonization and on the induced resistance were intermediate and high, respectively. Subsequently, Ri was chosen to inoculate ethylene-insensitive tomato mutant line Never ripe (Nr) and its background (Pearson)...