Arbuscular Mycorrhizal Symbiosis Differentially Affects the Nutritional Status of Two Durum Wheat Genotypes under Drought Conditions

Ionome profiling discriminate genotype-dependent responses to drought in durum wheat

Low-resource environments, such as dry or infertile soils, result in limited plant growth and development, which in turn constrain crop productivity. Water shortage is a significant threat to agricultural productivity all over the world. Drought may also affect plant nutrient uptake and assimilation capability causing nutrient deficiencies even in fertilized fields. Durum wheat is an important staple food crop for ensuring food security in the Mediterranean area, which is increasingly subjected to periods of severe drought due to global changes. Thus, identifying wheat cultivars/genotypes able to cope with suboptimal water, and with unbalanced nutrient availability deriving from drought is crucial to mitigate climate change's adverse effects on agriculture. In this study, a detailed analysis of the phenome, including biomass production, proline production, and characterization of root system architecture, and the ionome, was performed on a panel of 15 Triticum turgidum genotypes, differing for drought tolerance, in order to understand the genotype-specific physiological responses to drought and to identify those genotypes characterised by a positive correlation between ion homeostasis and drought response. The characterization of root system architecture helped our understanding of the morphological responses of wheat plants to drought. Our findings demonstrated that drought exposure for 7 days significantly impacted the ionomic profiles of most genotypes in both shoot and root tissues, albeit to varying degrees. The Lcye A-B- genotype showed the highest accumulation efficiency for most nutrients in shoots, while Bulel tritordeum and Karim in roots. It is also important to understand how micronutrients interact with each other and with macronutrients. Thus, we performed a nutrient correlation network analysis, which showed that drought altered the interactions between nutrients in most genotypes. These findings underscore the importance of understanding the mechanisms regulating nutrient homeostasis, as these mechanisms can either mitigate or exacerbate the impact of drought stress. Understanding the interplay between ionomic profiles and environmental conditions can provide valuable insights into developing more resilient crops that can thrive in challenging environments, ultimately contributing to global food security in the face of climate change.

Effect of exogenous treatment with zaxinone and its mimics on rice root microbiota across different growth stages

Enhancing crops productivity to ensure food security is one of the major challenges encountering agriculture today. A promising solution is the use of biostimulants, which encompass molecules that enhance plant fitness, growth, and productivity. The regulatory metabolite zaxinone and its mimics (MiZax3 and MiZax5) showed promising results in improving the growth and yield of several crops. Here, the impact of their exogenous application on soil and rice root microbiota was investigated. Plants grown in native paddy soil were treated with zaxinone, MiZax3, and MiZax5 and the composition of bacterial and fungal communities in soil, rhizosphere, and endosphere at the tillering and the milky stage was assessed. Furthermore, shoot metabolome profile and nutrient content of the seeds were evaluated. Results show that treatment with zaxinone and its mimics predominantly influenced the root endosphere prokaryotic community, causing a partial depletion of plant-beneficial microbes at the tillering stage, followed by a recovery of the prokaryotic community structure during the milky stage. Our study provides new insights into the role of zaxinone and MiZax in the interplay between rice and its root-associated microbiota and paves the way for their practical application in the field as ecologically friendly biostimulants to enhance crop productivity.

Arbuscular Mycorrhizal Fungi: Boosting Crop Resilience to Environmental Stresses

Amid escalating challenges from global climate change and increasing environmental degradation, agricultural systems worldwide face a multitude of abiotic stresses, including drought, salinity, elevated temperatures, heavy metal pollution, and flooding. These factors critically impair crop productivity and yield. Simultaneously, biotic pressures such as pathogen invasions intensify the vulnerability of agricultural outputs. At the heart of mitigating these challenges, Arbuscular Mycorrhizal Fungi (AM fungi) form a crucial symbiotic relationship with most terrestrial plants, significantly enhancing their stress resilience. AM fungi improve nutrient uptake, particularly that of nitrogen and phosphorus, through their extensive mycelial networks. Additionally, they enhance soil structure, increase water use efficiency, and strengthen antioxidant defense mechanisms, particularly in environments stressed by drought, salinity, extreme temperatures, heavy metal contamination, and flooding. Beyond mitigating abiotic stress, AM fungi bolster plant defenses against pathogens and pests by competing for colonization sites and enhancing plant immune responses. They also facilitate plant adaptation to extreme environmental conditions by altering root morphology, modulating gene expression, and promoting the accumulation of osmotic adjustment compounds. This review discusses the role of AM fungi in enhancing plant growth and performance under environmental stress.

Integrating Physiology, Transcriptome, and Metabolome Analyses Reveals the Drought Response in Two Quinoa Cultivars with Contrasting Drought Tolerance

Quinoa (Chenopodium quinoa Willd.) is an annual broadleaf plant belonging to the Amaranthaceae family. It is a nutritious food crop and is considered to be drought-tolerant, but drought is still one of the most important abiotic stress factors limiting its yield. Quinoa responses to drought are related to drought intensity and genotype. This study used two different drought-responsive quinoa cultivars, LL1 (drought-tolerant) and ZK1 (drought-sensitive), to reveal the important mechanisms of drought response in quinoa by combining physiological, transcriptomic, and metabolomic analyses. The physiological analysis indicated that Chla/Chlb might be important for drought tolerance in quinoa. A total of 1756 and 764 differentially expressed genes (DEGs) were identified in LL1 and ZK1, respectively. GO (Gene Ontology) enrichment analysis identified 52 common GO terms, but response to abscisic acid (GO:0009737) and response to osmotic stress (GO:0006970) were only enriched in LL1. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis revealed that glycerophospholipid metabolism (ko00564) and cysteine and methionine metabolism (ko00270) ranked at the top of the list in both cultivars. A total of 1844 metabolites were identified by metabolomic analysis. "Lipids and lipid-like" molecules had the highest proportions. The DEMs in LL1 and ZK1 were mainly categorized 6 and 4 Human Metabolome Database (HMDB) superclasses, respectively. KEGG analysis revealed that the 'α-linolenic acid metabolism' was enriched in both LL1 and ZK1. Joint KEGG analysis also revealed that the 'α-linolenic acid metabolism' pathway was enriched by both the DEGs and DEMs of LL1. There were 17 DEGs and 8 DEMs enriched in this pathway, and methyl jasmonate (MeJA) may play an important role in the drought response of quinoa. This study will provide information for the identification of drought resistance in quinoa, research on the molecular mechanism of drought resistance, and genetic breeding for drought resistance in quinoa.

The drought-induced plasticity of mineral nutrients contributes to drought tolerance discrimination in durum wheat

Drought is a major challenge for the cultivation of durum wheat, a crucial crop for global food security. Plants respond to drought by adjusting their mineral nutrient profiles to cope with water scarcity, showing the importance of nutrient plasticity for plant acclimation and adaptation to diverse environments. Therefore, it is essential to understand the genetic basis of mineral nutrient profile plasticity in durum wheat under drought stress to select drought-tolerant varieties. The research study investigated the responses of different durum wheat genotypes to severe drought stress at the seedling stage. The study employed an ionomic, molecular, biochemical and physiological approach to shed light on distinct behaviors among different genotypes. The drought tolerance of SVEMS16, SVEVO, and BULEL was related to their capacity of maintaining or increasing nutrient's accumulation, while the limited nutrient acquisition capability of CRESO and S.CAP likely resulted in their susceptibility to drought. The study highlighted the importance of macronutrients such as SO42-, NO3-, PO43-, and K+ in stress resilience and identified variant-containing genes potentially influencing nutritional variations under drought. These findings provide valuable insights for further field studies to assess the drought tolerance of durum wheat genotypes across various growth stages, ultimately ensuring food security and sustainable production in the face of changing environmental conditions.

Rye-durum wheat 1BL.1RS translocation: implications for drought tolerance and nutritional status

The translocation of the short chromosome arm 1RS of rye onto the 1B chromosome of common wheat has been shown to improve resistance to stress and yield. Here, translocation was operated in durum wheat and its effects on drought tolerance were evaluated. Both the 1BL.1RS translocation line (Svevo 1BL.1RS) and the corresponding Svevo control were exposed to drought for 7 days. Significant differences were found in root morphology between Svevo and Svevo 1BL.1RS under control and drought conditions. Although Svevo 1BL.1RS experienced more severe growth inhibition due to drought than Svevo, it exhibited greater resilience to oxidative stress. Furthermore, several drought-responsive genes were upregulated in both shoots and roots only in the translocation line. Notably, in roots of Svevo 1BL.1RS, the expression of these genes was also higher in the control condition compared to Svevo, suggesting that these genes could be constitutively expressed at higher levels in the translocation line. Moreover, the 1BL.1RS translocation had a significant impact on the plant's ability to accumulate nutrients under drought. Overall, the impact on sulfate accumulation and the expression of genes associated with its assimilation pathways are particularly noteworthy, highlighting the involvement of sulfur in the plant response to water stress. Additionally, the genetic characterization of Svevo 1BL.1RS revealed variants extending beyond the translocation, located in drought stress-responsive genes.

Wheat dwarfing reshapes plant and fungal development in arbuscular mycorrhizal symbiosis

The introduction of Reduced height (Rht) dwarfing genes into elite wheat varieties has contributed to enhanced yield gain in high input agrosystems by preventing lodging. Yet, how modern selection for dwarfing has affected symbiosis remains poorly documented. In this study, we evaluated the response of both the plant and the arbuscular mycorrhizal fungus to plant genetic variation at a major Quantitative Trait Locus called QTL 4B2, known to harbor a Rht dwarfing gene, when forming the symbiosis. We used twelve inbred genotypes derived from a diversity base broadened durum wheat Evolutionary Pre-breeding Population and genotyped with a high-throughput Single Nucleotide Polymorphism (SNP) genotyping array. In a microcosm setup segregating roots and the extra-radical mycelium, each wheat genotype was grown with or without the presence of Rhizophagus irregularis. To characterize arbuscular mycorrhizal symbiosis, we assessed hyphal density, root colonization, spore production, and plant biomass. Additionally, we split the variation of these variables due either to genotypes or to the Rht dwarfing genes alone. The fungus exhibited greater development in the roots of Dwarf plants compared to non-Dwarf plants, showing increases of 27%, 37% and 51% in root colonization, arbuscules, and vesicles, respectively. In addition, the biomass of the extra-radical fungal structures increased by around 31% in Dwarf plants. The biomass of plant roots decreased by about 43% in mycorrhizal Dwarf plants. Interestingly, extraradical hyphal production was found to be partly genetically determined with no significant effect of Rht, as for plant biomasses. In contrast, variations in root colonization, arbuscules and extraradical spore production were explained by Rht dwarfing genes. Finally, when mycorrhizal, Dwarf plants had significantly lower total P content, pointing towards a less beneficial symbiosis for the plant and increased profit for the fungus. These results highlight the effect of Rht dwarfing genes on both root and fungal development. This calls for further research into the molecular mechanisms governing these effects, as well as changes in plant physiology, and their implications for fostering arbuscular mycorrhizal symbiosis in sustainable agrosystems.

Design of Microbial Consortia Based on Arbuscular Mycorrhizal Fungi, Yeasts, and Bacteria to Improve the Biochemical, Nutritional, and Physiological Status of Strawberry Plants Growing under Water Deficits

Drought affects several plant physiological characteristics such as photosynthesis, carbon metabolism, and chlorophyll content, causing hormonal and nutritional imbalances and reducing nutrient uptake and transport, which inhibit growth and development. The use of bioinoculants based on plant growth-promoting microorganisms such as plant growth-promoting rhizobacteria (PGPR), yeasts, and arbuscular mycorrhizal fungi (AMF) has been proposed as an alternative to help plants tolerate drought. However, most studies have been based on the use of a single type of microorganism, while consortia studies have been scarcely performed. Therefore, the aim of this study was to evaluate different combinations of three PGPR, three AMF, and three yeasts with plant growth-promoting attributes to improve the biochemical, nutritional, and physiological behavior of strawberry plants growing under severe drought. The results showed that the growth and physiological attributes of the non-inoculated plants were significantly reduced by drought. In contrast, plants inoculated with the association of the fungus Claroideoglomus claroideum, the yeast Naganishia albida, and the rhizobacterium Burkholderia caledonica showed a stronger improvement in tolerance to drought. High biomass, relative water content, fruit number, photosynthetic rate, transpiration, stomatal conductance, quantum yield of photosystem II, N concentration, P concentration, K concentration, antioxidant activities, and chlorophyll contents were significantly improved in inoculated plants by up to 16.6%, 12.4%, 81.2%, 80%, 79.4%, 71.0%, 17.8%, 8.3%, 6.6%, 57.3%, 41%, and 22.5%, respectively, compared to stressed non-inoculated plants. Moreover, decreased malondialdehyde levels by up to 32% were registered. Our results demonstrate the feasibility of maximizing the effects of inoculation with beneficial rhizosphere microorganisms based on the prospect of more efficient combinations among different microbial groups, which is of interest to develop bioinoculants oriented to increase the growth of specific plant species in a global scenario of increasing drought stress.

Microbial consortia and biochar as sustainable biofertilisers: Analysis of their impact on wheat growth and production

The European Union is among the top wheat producers in the world, but its productivity relies on adequate soil fertilisation. Biofertilisers, either alone or in combination with biochar, can be a preferable alternative to chemical fertilisers. However, the addition of biofertilisers, specifically plant growth promoting microbes (PGPM), could modify grain composition, and/or deteriorate the soil composition. In this study, the two wheat cultivars Triticum aestivum (Bramante) and T. durum (Svevo) were cultivated in open fields for two consecutive years in the presence of a commercial PGPM mix supplied alone or in combination with biochar. An in-depth analysis was conducted by collecting physiological and agronomic data throughout the growth period. The effects of PGPM and biochar were investigated in detail; specifically, soil chemistry and rhizosphere microbial composition were characterized, along with the treatment effects on seed storage proteins. The results demonstrated that the addition of commercial microbial consortia and biochar, alone or in combination, did not modify the rhizospheric microbial community; however, it increased grain yield, especially in the cultivar Svevo (increase of 6.8 %-13.6 %), even though the factors driving the most variations were associated with both climate and cultivar. The total gluten content of the flours was not affected, whereas the main effect of the treatments was a variation in gliadins and low-molecular-weight-glutenin subunits in both cultivars when treated with PGPM and biochar. This suggested improved grain quality, especially regarding the viscoelastic properties of the dough, when the filling period occurred in a dry climate. The results indicate that the application of biofertilisers and biochar may aid the effective management of sustainable wheat cultivation, to support environmental health without altering the biodiversity of the resident microbiome.

Signals and Machinery for Mycorrhizae and Cereal and Oilseed Interactions towards Improved Tolerance to Environmental Stresses

In the quest for sustainable agricultural practices, there arises an urgent need for alternative solutions to mineral fertilizers and pesticides, aiming to diminish the environmental footprint of farming. Arbuscular mycorrhizal fungi (AMF) emerge as a promising avenue, bestowing plants with heightened nutrient absorption capabilities while alleviating plant stress. Cereal and oilseed crops benefit from this association in a number of ways, including improved growth fitness, nutrient uptake, and tolerance to environmental stresses. Understanding the molecular mechanisms shaping the impact of AMF on these crops offers encouraging prospects for a more efficient use of these beneficial microorganisms to mitigate climate change-related stressors on plant functioning and productivity. An increased number of studies highlighted the boosting effect of AMF on grain and oil crops' tolerance to (a)biotic stresses while limited ones investigated the molecular aspects orchestrating the different involved mechanisms. This review gives an extensive overview of the different strategies initiated by mycorrhizal cereal and oilseed plants to manage the deleterious effects of environmental stress. We also discuss the molecular drivers and mechanistic concepts to unveil the molecular machinery triggered by AMF to alleviate the tolerance of these crops to stressors.

Tomato plant growth promotion and drought tolerance conferred by three arbuscular mycorrhizal fungi is mediated by lipid metabolism

Arbuscular mycorrhizal fungi (AMF) can promote plant growth and enhance plant drought tolerance with varying effect size among different fungal species. However, the linkage between the variation and the lipid metabolism, which is exclusively derived from plants, has been little explored thus far. Here, we established AM symbiosis between tomato (Solanum lycopersicum) plants and three AMF species (Rhizophagus intraradices, Funneliformis mosseae, Rhizophagus irregularis) under well watered (WW) or drought stressed (DS) conditions in pot experiment. The plant biomass, chlorophyll fluorescence Fv/Fm, shoot P content and mycorrhizal colonization were determined. Meanwhile, fatty acid (FA) profiles and relative expression of genes encoding for nutrition exchange (SlPT4, SlPT5, RAM2, STR/STR2) in roots were also monitored. DS significantly decreased plant biomass while AMF significantly increased it, with three fungal species varying in their growth promoting capacity and drought tolerance capacity. The growth promoting effect of R. irregularis was lower than those of R. intraradices and F. mosseae, and was associated with higher mycorrhizal colonization and more consumption of lipids. However, the drought tolerance capacity of R. irregularis was greater than those of R. intraradices and F. mosseae, and was associated with less decrease in mycorrhizal colonization and lipid content. We also found that AMF mediated plant drought tolerance via regulating both AM specific FAs and non-AM specific FAs in a complementary manner. These data suggest that lipid metabolism in AM plays a crucial role in plant drought tolerance mediated by AMF.

Molecular and Systems Biology Approaches for Harnessing the Symbiotic Interaction in Mycorrhizal Symbiosis for Grain and Oil Crop Cultivation

Mycorrhizal symbiosis, the mutually beneficial association between plants and fungi, has gained significant attention in recent years due to its widespread significance in agricultural productivity. Specifically, arbuscular mycorrhizal fungi (AMF) provide a range of benefits to grain and oil crops, including improved nutrient uptake, growth, and resistance to (a)biotic stressors. Harnessing this symbiotic interaction using molecular and systems biology approaches presents promising opportunities for sustainable and economically-viable agricultural practices. Research in this area aims to identify and manipulate specific genes and pathways involved in the symbiotic interaction, leading to improved cereal and oilseed crop yields and nutrient acquisition. This review provides an overview of the research frontier on utilizing molecular and systems biology approaches for harnessing the symbiotic interaction in mycorrhizal symbiosis for grain and oil crop cultivation. Moreover, we address the mechanistic insights and molecular determinants underpinning this exchange. We conclude with an overview of current efforts to harness mycorrhizal diversity to improve cereal and oilseed health through systems biology.

Phenylalanine supply alleviates the drought stress in mustard (Brassica campestris) by modulating plant growth, photosynthesis, and antioxidant defense system

Mustard (Brassica campestris L.) is a major oilseed crop that plays a crucial role in agriculture. Nevertheless, a number of abiotic factors, drought in particular, significantly reduce its production. Phenylalanine (PA) is a significant and efficacious amino acid in alleviating the adverse impacts of abiotic stressors, such as drought. Thus, the current experiment aimed to evaluate the effects of PA application (0 and 100 mg/L) on brassica varieties i.e., Faisal (V1) and Rachna (V2) under drought stress (50% field capacity). Drought stress reduced the shoot length (18 and 17%), root length (12.1 and 12.3%), total chlorophyll contents (47 and 45%), and biological yield (21 and 26%) of both varieties (V1 and V2), respectively. Foliar application of PA helped overcome drought-induced losses and enhanced shoot length (20 and 21%), total chlorophyll contents (46 and 58%), and biological yield (19 and 22%), whereas reducing the oxidative activities of H2O2 (18 and 19%), MDA concentration (21 and 24%), and electrolyte leakage (19 and 21%) in both varieties (V1 and V2). Antioxidant activities, i.e., CAT, SOD, and POD, were further enhanced under PA treatment by 25, 11, and 14% in V1 and 31, 17, and 24% in V2. Overall findings suggest that exogenous PA treatment reduced the drought-induced oxidative damage and improved the yield, and ionic contents of mustard plants grown in pots. It should be emphasized, however, that studies examining the impacts of PA on open-field-grown brassica crops are still in their early stages, thus more work is needed in this area.

Arbuscular Mycorrhizal Fungi Enhance Biomass Growth, Mineral Content, and Antioxidant Activity in Tomato Plants under Drought Stress

Arbuscular mycorrhizal fungi (AMF) are symbiotically associated with crops. They increase biomass production, nutritional elements, and antioxidant activities in food and vegetable crops grown in soil under stress conditions. The present study focused on the effects of AMF (Acaulospora morrowiae, Paraglomus occultum, Funneliformis mosseae, Rhizophagus clarus, and Rhizophagus intraradices) on biomass growth and yield, contents of chlorophyll and carotenoids, activities of catalase (CAT) and ascorbate peroxidase (APX), and contents of hydrogen peroxide (H2O2), malondialdehyde (MDA), and minerals (Na, K, Ca, Mg, and Fe) in Unnayan, LT896, and Minto super tomato (Solanum lycopersicum L.) varieties grown in soil under drought stress (<10% moisture). The results showed that root length and shoot mass in plants treated with R. clarus and P. occultum were significantly higher than those of the control (non-AMF) in Minto super tomato. Compared to the control, the shoot’s dry weight and yield were enhanced by 28% and 20% with AMF-treated tomatoes. The CAT activity in P. occultum-treated plants was statistically higher than that of the control in Unnayan tomatoes. H2O2 content was detected higher in the control than R. clarus-treated LT896 tomatoes. In plants treated with A. morrowiae and R. clarus, APX activity was significantly higher than that of the control in the Unnayan tomatoes. CAT and APX activity increased by 42% and 66% in AMF-treated leaves of tomatoes compared to non-AMF. Treatment with AMF reduced the content of MDA and H2O2 (ROS) in the leaves of tomato plants by 50% and 2% compared to the control, respectively. Potassium (K), calcium (Ca), magnesium (Mg), and iron (Fe) of tomato fruits increased by 2%, 13%, 24%, and 37% with AMF treatment compared to the control. These results suggested that biomass growth, yield, photosynthetic pigments, antioxidant enzyme activity, and mineral contents could be enhanced by AMF in food crops grown under drought stress. It is concluded that AMF might be used for the development of AMF-enriched biofertilizers that will improve the nutritional quality of food crops grown under stress conditions.

SHINE clade of ERF transcription factors: A significant player in abiotic and biotic stress tolerance in plants

SHINE (SHN) clade transcription factors (TFs) represents a subfamily of APETALA2/ethylene-responsive factor (AP2/ERF) proteins. The latter, is characterized by its responsiveness to the phytohormone ethylene and the presence of AP2 DNA-binding domain. They are involved in many biological processes and in responses to different environmental constraints. SHN TFs were among the first identified regulators of cuticle formation. Cuticle plays crucial role in plant tolerance to drought, salinity and high temperature as well as in defense against pathogens. In addition, SHN were shown to be involved in the regulation of stomatal development which influences resistance to drought and diseases. Interestingly, recent studies have also shown that SHN TFs are involved in mediating the beneficial effects of arbuscular mycorrhizal fungi (AMF) as well as disease resistance conferred by nanoparticles. To fulfill their roles, SHN TFs are controlled upstream by other TFs and they control, in their turn, different downstream genes. In this review, we highlight the role of SHN TFs in different abiotic and biotic stresses through their involvement in cuticle biosynthesis, stomatal development and molecular regulation of biochemical and physiological traits. In addition, we discuss the regulation of SHN TFs by plant hormones and their influence on hormone biosynthesis and signaling pathways. Knowledge of this complex regulation can be put into contribution to increase multiple abiotic stress tolerances through transgenesis, gene editing and classical breeding.

AMF species do matter: Rhizophagus irregularis and Funneliformis mosseae affect healthy and PVY-infected Solanum tuberosum L. in a different way

Arbuscular mycorrhizal fungi (AMF) were documented to positively influence plant growth and yield, which is extremely important for the production of many crops including potato. However, the nature of the interaction between arbuscular mycorrhiza and plant virus that share the same host is not well characterized. In this study, we examined the effect of different AMF, Rhizophagus irregularis and Funneliformis mosseae, on healthy and potato virus Y (PVY)-infected Solanum tuberosum L. The analyses conducted included the measurement of potato growth parameters, oxidative stress indicators, and photosynthetic capacity. Additionally, we evaluated both the development of AMF in plant roots and the virus level in mycorrhizal plants. We found that two AMF species colonized plant roots to varying degrees (ca. 38% for R. irregularis vs. 20% for F. mosseae). Rhizophagus irregularis had a more positive effect on potato growth parameters, causing a significant increase in the total fresh and dry weight of tubers, along with virus-challenged plants. Furthermore, this species lowered hydrogen peroxide levels in PVY-infected leaves and positively modulated the levels of nonenzymatic antioxidants, i.e., ascorbate and glutathione in leaves and roots. Finally, both fungal species contributed to reduced lipid peroxidation and alleviation of virus-induced oxidative damage in plant organs. We also confirmed an indirect interaction between AMF and PVY inhabiting the same host. The two AMF species seemed to have different abilities to colonize the roots of virus-infected hosts, as R. irregularis showed a stronger drop in mycorrhizal development in the presence of PVY. At the same time, arbuscular mycorrhiza exerted an effect on virus multiplication, causing increased PVY accumulation in plant leaves and a decreased concentration of virus in roots. In conclusion, the effect of AMF-plant interactions may differ depending on the genotypes of both symbiotic partners. Additionally, indirect AMF-PVY interactions occur in host plants, diminishing the establishment of arbuscular mycorrhiza while changing the distribution of viral particles in plants.

The effect of rhizobia in improving the protective mechanisms of wheat under drought and supplementary irrigation conditions

Introduction

Wheat (Triticum aestivum L.) is a strategic crop and one of the world's most essential cereals, providing most of the world's calories and protein needs. Drought stress is one of the main limitations for crop production such as wheat in arid and semi-arid regions. Plants can accumulate antioxidants, carbohydrates, and stress hormones that stimulate cell and molecular regeneration under stress conditions. Irrigation saves water, improves crop photosynthesis, and increases plant ability to absorb water and elements from soil. Therefore, irrigation at the right time or supplementary irrigation can help plant growth and crop yield under drought conditions. Appropriate nutrition with fertilizers increases plants' stress tolerance. Bio-fertilizers are restorative elements used in soil to improve tolerance to stresses such as drought stress. A well-known class of bio-fertilizers is plant growth promoting rhizobacteria (PGPR). These rhizosphere bacteria affect plant development and productivity by interacting with roots. Arbuscular mycorrhizal fungi (AMF) alleviate drought stress in plants by enhancing their ability to absorb water and nutrients from the soil. Seaweed extract bio-fertilizer is organic matter used to increase crop growth and soil fertility. This bio-fertilizer is utilized as growth stimulants and food supplements. Our research analyzed the effects of rhizobia and seaweed extracts on wheat's drought resistance mechanisms.

Materials and methods

This research was conducted in Iran in the crop years of 2017–2018 and 2018–2019 in the research farm of Kurdistan University Faculty of Agriculture located in Dehgolan with coordinates 47°18′ 55″ East and 35°19′ 10″ North with an altitude of 1866 meters above sea level, 45 kilometers east It was done on the wheat plant in Sanandaj city. The experiment was conducted in the form of a split-split plot in the form of a randomized complete block design with four replications. Irrigation treatments as the main factor (no irrigation or dry-land, one irrigation in the booting stage, two irrigations in the booting and spike stages), two wheat cultivars (Sardari and Sirvan) as secondary factors, and the application of biological fertilizers at eight levels including Mycorrhiza + Nitrozist and Phosphozist, Seaweed extract + Nitrozist and Phosphozist, Mycorrhiza + Seaweed extract, Mycorrhiza + Nitrozist and Phosphozist and no application of biological fertilizers (control) as Sub-sub-factors were considered.

Results and discussion

According to the study, when bio-fertilizer was applied with once and twice supplementary irrigation levels, leaf relative water content (RWC) and soluble protein content (SPC) increased, while lack of irrigation increased malondialdehyde (MDA). In both years, bio-fertilizers, especially their combinations, increased the amount and activity of enzymatic and non-enzymatic antioxidants, including peroxidase (POD), superoxide dismutase (SOD), phenol (Phe), flavonoid (Fla), and anthocyanin (Anth). Also, it enhanced the inhibition of free radicals by 2-2-Diphenyl picryl hydrazyl (DPPH) and cleared active oxygen species. It was found that malondialdehyde (MDA) levels were very low in wheat under two times irrigation with averages of 3.3909 and 3.3865 μmol g−1 FW. The results indicated a significant positive relationship between non-enzymatic and enzymatic antioxidants such as Phe, Fla, Anth, DPPH, POD, and SOD enzymes and their role in improving stress under dry-land conditions, especially in the Sardari variety. Biological fertilizers (Mycorrhiza + Nitrozist and Phosphozist + Seaweed extract) increased wheat yield compared to the control. Furthermore, Mycorrhiza + Nitrozist and Phosphozist + Seaweed extract improved grain yield by 8.04% and 6.96% in the 1st and 2nd years, respectively. Therefore, appropriate combinations of microorganisms, beneficial biological compounds, and supplementary irrigation can reduce the adverse effects of drought stress in arid and semi-arid regions.

Arbuscular Mycorrhizal Symbiosis: A Strategy for Mitigating the Impacts of Climate Change on Tropical Legume Crops

Climate change is likely to have severe impacts on food security in the topics as these regions of the world have both the highest human populations and narrower climatic niches, which reduce the diversity of suitable crops. Legume crops are of particular importance to food security, supplying dietary protein for humans both directly and in their use for feed and forage. Other than the rhizobia associated with legumes, soil microbes, in particular arbuscular mycorrhizal fungi (AMF), can mitigate the effects of biotic and abiotic stresses, offering an important complementary measure to protect crop yields. This review presents current knowledge on AMF, highlights their beneficial role, and explores the potential for application of AMF in mitigating abiotic and biotic challenges for tropical legumes. Due to the relatively little study on tropical legume species compared to their temperate growing counterparts, much further research is needed to determine how similar AMF-plant interactions are in tropical legumes, which AMF species are optimal for agricultural deployment and especially to identify anaerobic AMF species that could be used to mitigate flood stress in tropical legume crop farming. These opportunities for research also require international cooperation and support, to realize the promise of tropical legume crops to contribute to future food security.

The Influence of Arbuscular Mycorrhizal Fungus Rhizophagus irregularis on the Growth and Quality of Processing Tomato (Lycopersicon esculentum Mill.) Seedlings

Tomato (Lycopersicon esculentum Mill.) is one of the most valuable horticultural crops, not only for its economic importance but also for its high nutritional value and sensory qualities. The arbuscular mycorrhiza (AM) fungus Rhizophagus irregularis can improve plant nutrient uptake and decrease seedling transplanting shock. Although R. irregularis is one of the most extensively studied AMF species, there is a paucity of data on the effects of this species on processing tomato seedlings produced in an aerated hydroponic float system. A greenhouse experiment with four treatments and three replications was established in a completely randomized design. The treatments contained the addition of 0, 40, 80, and 120 fungal spores per L of nutrient solution (control, AMF1, AMF2, and AMF3, respectively). Root colonization analysis proved that the maximum dose of applied AMF (AMF3) supported colonization to a large extent, succeeding 36.74%. In addition, the highest values of total dry weight (1.386 g), survival rate (94.79%), N content (3.376 mg per 100 g DW) and P content (0.497 mg per 100 g DW) were also observed under AMF3 treatment. In conclusion, the application of high doses of the AM fungus R. irregularis in nutrient solutions of float system leads to a substantial improvement in the quality and growth of processing tomato seedlings.

The Critical Role of Arbuscular Mycorrhizal Fungi to Improve Drought Tolerance and Nitrogen Use Efficiency in Crops

Drought stress (DS) is a serious abiotic stress and a major concern across the globe as its intensity is continuously climbing. Therefore, it is direly needed to develop new management strategies to mitigate the adverse effects of DS to ensure better crop productivity and food security. The use of arbuscular mycorrhizal fungi (AMF) has emerged as an important approach in recent years to improve crop productivity under DS conditions. AMF establishes a relationship with 80% of land plants and it induces pronounced impacts on plant growth and provides protection to plants from abiotic stress. Drought stress significantly reduces plant growth and development by inducing oxidative stress, disturbing membrane integrity, plant water relations, nutrient uptake, photosynthetic activity, photosynthetic apparatus, and anti-oxidant activities. However, AMF can significantly improve the plant tolerance against DS. AMF maintains membrane integrity, improves plant water contents, nutrient and water uptake, and water use efficiency (WUE) therefore, improve the plant growth under DS. Moreover, AMF also protects the photosynthetic apparatus from drought-induced oxidative stress and improves photosynthetic efficiency, osmolytes, phenols and hormone accumulation, and reduces the accumulation of reactive oxygen species (ROS) by increasing anti-oxidant activities and gene expression which provide the tolerance to plants against DS. Therefore, it is imperative to understand the role of AMF in plants grown under DS. This review presented the different functions of AMF in different responses of plants under DS. We have provided a detailed picture of the different mechanisms mediated by AMF to induce drought tolerance in plants. Moreover, we also identified the potential research gaps that must be fulfilled for a promising future for AMF. Lastly, nitrogen (N) is an important nutrient needed for plant growth and development, however, the efficiency of applied N fertilizers is quite low. Therefore, we also present the information on how AMF improves N uptake and nitrogen use efficiency (NUE) in plants.