Comparative Analysis of the Combined Effects of Different Water and Phosphate Levels on Growth and Biological Nitrogen Fixation of Nine Cowpea Varieties

A bamboo bHLH transcription factor PeRHL4 has dual functions in enhancing drought and phosphorus starvation tolerance

ROOTHAIRLESS (RHL) is a typical type of basic helix-loop-helix (bHLH) transcription factor (TF), which has been reported to participate in various aspects of plant growth and in response to stress. However, the functions of RHL subfamily members in moso bamboo (Phyllostachys edulis) remain unknown. In this study, we identified 14 bHLH genes (PeRHL1-PeRHL14) in moso bamboo. Phylogenetic tree and conserved motif analyses showed that PeRHLs were clustered into three clades. The expression analysis suggested that PeRHL4 was co-expressed with PeTIP1-1 and PePHT1-1 in moso bamboo. Moreover, these three genes were all up-regulated in moso bamboo under drought stress and phosphate starvation. Y1H, DLR and EMSA assays demonstrated that PeRHL4 could activate the expression of PeTIP1-1 and PePHT1-1. Furthermore, overexpression of PeRHL4 could increase both drought and phosphate starvation tolerance in transgenic rice, in which the expression of OsTIPs and OsPHT1s was significantly improved, respectively. Overall, our results indicated that drought stress and phosphate starvation could induce the expression of PeRHL4, which in turn activated downstream genes involved in water and phosphate transport. Collectively, our findings reveal that PeRHL4 acting as a positive regulator contributes to enhancing the tolerance of moso bamboo under drought stress and phosphate starvation.

Mineral and Carbon Metabolic Adjustments in Nodules of Symbiotically Grown Faba Bean (Vicia faba L.) Varieties in Response to Organic Phosphorus Supplementation

Phosphorus (P) is a major limiting factor for legume and symbiotic nitrogen fixation (SNF). Although overall adaptations of legumes to P supplementation have been extensively studied in connection with inorganic P, little information is currently available regarding nodulation or SNF responses to organic P (Po) in hydroponics. We investigated the mineral and carbon metabolism of Po-induced nodules of two contrasting faba bean varieties grown hydroponically under inorganic P (Pi), viz., in P-deficient (2 µM KH2PO4, -Pi), sufficient-P (200 µM KH2PO4, +Pi), and phytic acid (200 µM, Po) conditions, and were inoculated with Rhizobium leguminosarum bv. viciae 3841 and grown for 30 days. The results consistently reveal similar growth and biomass partitioning patterns between +Pi and Po, with both varying substantially from -Pi. In comparison, +Pi and Po observed equivalent accumulations of overall elemental P concentrations, with both increasing by 114 and 119%, respectively, relative to -Pi. A principal component analysis on metabolites showed a clear separation of the -Pi treatment from the others, with +Pi and Po correlating closely together, highlighting the nonsignificant differences between them. Additionally, the δ15N abundance of shoots, roots, and nodules was not significantly different between treatments and varieties and exhibited negative δ15N signatures for all tissues. Our study provides a novel perspective on mineral and carbon metabolism and their regulation of the growth, functioning, and reprogramming of nodules upon phytate supply.

Bioinoculants as a means of increasing crop tolerance to drought and phosphorus deficiency in legume-cereal intercropping systems

Ensuring plant resilience to drought and phosphorus (P) stresses is crucial to support global food security. The phytobiome, shaped by selective pressures, harbors stress-adapted microorganisms that confer host benefits like enhanced growth and stress tolerance. Intercropping systems also offer benefits through facilitative interactions, improving plant growth in water- and P-deficient soils. Application of microbial consortia can boost the benefits of intercropping, although questions remain about the establishment, persistence, and legacy effects within resident soil microbiomes. Understanding microbe- and plant-microbe dynamics in drought-prone soils is key. This review highlights the beneficial effects of rhizobacterial consortia-based inoculants in legume-cereal intercropping systems, discusses challenges, proposes a roadmap for development of P-solubilizing drought-adapted consortia, and identifies research gaps in crop-microbe interactions.

Comprehensive sequence and expression profile analysis of the phosphate transporter gene family in soybean

The family of phosphate transporters (PHTs) mediates the uptake and translocation of Pi inside the plants. However, little is known about transporters in soybean. Therefore, Searched the Genome Database for Soybean, 57 GmPHTs family members were identified in soybean, Phylogenetic analysis suggested that members of the PHTs gene family can be divided into six clades. Collinearity analysis revealed that most of the GmPHT genes shared syntenic relationships with PHTs members in Arabidopsis thaliana and that large segment duplication played a major driving force for GmPHTs evolution in addition to tandem duplication. Further analysis of the promoter revealed that light-responsive elements and abiotic stress-responsive elements were widely distributed within the promoter regions of GmPHT genes. Based on RNA-seq data, GmPHTs showed different expression patterns in roots and leaves of soybean treated with long-term low phosphorus and short-term low phosphorus, in addition, the expression levels of GmPHT genes can be regulated by drought stresses, it was implied that the induced expression of GmPHTs could promote phosphorus uptake and transport in soybean and thus adapt to low phosphorus and drought stress, which is the first step dissection of Pi transport system and probably refers to new roles of PHTs genes in soybean.

Nitrogen fixation capacity and metabolite responses to phosphorus in soybean nodules

Phosphorus (P) is necessary for nitrogen fixation in the root nodules of soybeans, a symbiotic process whereby plants support bacterial nitrogen fixation to obtain nitrogen needed for plant growth. Nitrogen accumulation, quantity, weight, specific nitrogenase activity (SNA) and acetylene reduction activity (ARA) of root soybean nodules were analyzed, using a broadly targeted metabolomics method incorporating liquid chromatography-mass spectrometry (LC-MS) to study the effects of P level (1, 11, 31, 61 mg/L denoted by P1, P11, P31, P61) on the types and abundance of various metabolites and on the expression of associated metabolic pathways in soybean root nodules. Nitrogen accumulation, quantity, weight, SNA and ARA of root nodules were inhibited by P stress. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that root nodules responded to P stress by increasing the number of amino acids and derivatives. Down-regulation of ABA, phosphorylcholine, and D-glucose 6-phosphate affected carotenoid biosynthesis, glycerophospholipid metabolism and sugar metabolism which inhibited nodule nitrogen fixation under P stress. More flavonoids were involved in metabolic processes in soybean root nodules under P stress that regulated the nodulation and nitrogen fixation. The pathway ascorbate and aldarate metabolism, and associated metabolites, were involved in the adaptation of the symbiotic soybean root nodule system to P starvation. This work provides a foundation for future investigations of physiological mechanisms that underly phosphorus stress on soybeans.

Legume germination is delayed in dry soils and in sterile soils devoid of microbial mutualists: Species-specific implications for upward range expansions

Climate change is affecting species and their mutualists and can lead to the weakening or loss of important interspecific interactions. Through independent shifts in partner phenology and distribution, climatic stress can separate mutualists temporally or spatially, leading to alterations in partner functional traits and fitness. Here, we explored the effects of the loss of microbial mutualists on legume germination success and phenology. In particular, we assessed the effects of mutualism loss via soil sterilization, increased drought, and introduction to novel soils found beyond the current distributions of two focal legume species in subalpine environments. Through common garden experiments in controlled environments, we found evidence that soil sterilization (and consequent microbial absence) and dry soils caused species-specific phenological delays of 2-5 weeks in germination, likely as a result of interaction loss between legumes and specialized germination-promoting soil microbes, such as mutualistic rhizobia. Delays in germination caused by a mismatch between legumes and beneficial microbes could negatively affect legume fitness through increased plant-plant competition later in the season. Additionally, we found evidence of the presence of beneficial microbes beyond the current elevational range of one of our focal legumes, which may allow for expansion of the leading edge, although harsh abiotic factors in the alpine may hinder this. Alterations in the strength of soil microbe-legume mutualisms may lead to reduced fitness and altered demography for both soil microbes and legumes.

Co-Inoculation with Azospirillum brasilense and Bradyrhizobium sp. Enhances Nitrogen Uptake and Yield in Field-Grown Cowpea and Did Not Change N-Fertilizer Recovery

This study was designed to investigate the effects of Azospirillum brasilense and Bradyrhizobium sp. co-inoculation coupled with N application on soil N levels and N in plants (total N, nitrate N-NO₃⁻ and ammonium N-NH₄⁺), photosynthetic pigments, cowpea plant biomass and grain yield. An isotopic technique was employed to evaluate ¹⁵N fertilizer recovery and derivation. Field trials involved two inoculations—(i) single Bradyrhizobium sp. and (ii) Bradyrhizobium sp. + A. brasilense co-inoculation—and four N fertilizer rates (0, 20, 40 and 80 kg ha⁻¹). The co-inoculation of Bradyrhizobium sp. + A. brasilense increased cowpea N uptake (an increase from 10 to 14%) and grain yield (an average increase of 8%) compared to the standard inoculation with Bradyrhizobium sp. specifically derived from soil and other sources without affecting ¹⁵N fertilizer recovery. There is no need for the supplementation of N via mineral fertilizers when A. brasilense co-inoculation is performed in a cowpea crop. However, even in the case of an NPK basal fertilization, applied N rates should remain below 20 kg N ha⁻¹ when co-inoculation with Bradyrhizobium sp. and A. brasilense is performed.

Breeding of Vegetable Cowpea for Nutrition and Climate Resilience in Sub-Saharan Africa: Progress, Opportunities, and Challenges

Currently, the world population is increasing, and humanity is facing food and nutritional scarcity. Climate change and variability are a major threat to global food and nutritional security, reducing crop productivity in the tropical and subtropical regions of the globe. Cowpea has the potential to make a significant contribution to global food and nutritional security. In addition, it can be part of a sustainable food system, being a genetic resource for future crop improvement, contributing to resilience and improving agricultural sustainability under climate change conditions. In malnutrition prone regions of sub-Saharan Africa (SSA) countries, cowpea has become a strategic dryland legume crop for addressing food insecurity and malnutrition. Therefore, this review aims to assess the contribution of cowpea to SSA countries as a climate-resilient crop and the existing production challenges and perspectives. Cowpea leaves and immature pods are rich in diverse nutrients, with high levels of protein, vitamins, macro and micronutrients, minerals, fiber, and carbohydrates compared to its grain. In addition, cowpea is truly a multifunctional crop for maintaining good health and for reducing non-communicable human diseases. However, as a leafy vegetable, cowpea has not been researched and promoted sufficiently because it has not been promoted as a food security crop due to its low yield potential, susceptibility to biotic and abiotic stresses, quality assurance issues, policy regulation, and cultural beliefs (it is considered a livestock feed). The development of superior cowpea as a leafy vegetable can be approached in different ways, such as conventional breeding and gene stacking, speed breeding, mutation breeding, space breeding, demand-led breeding, a pan-omics approach, and local government policies. The successful breeding of cowpea genotypes that are high-yielding with a good nutritional value as well as having resistance to biotics and tolerant to abiotic stress could also be used to address food security and malnutrition-related challenges in sub-Saharan Africa.

Grain Legume Yield Responses to Rhizobia Inoculants and Phosphorus Supplementation Under Ghana Soils: A Meta-Synthesis

A discrete number of studies have been conducted on the effects of rhizobia (Rhz) inoculants, phosphorus (P) management, and combined application of Rhz and P fertilizer on the enhancement of grain legume yield across soils of Ghana and elsewhere. However, the extent to which the various inoculated Rhz strains, P application, and combined application of Rhz + P studies contribute to improving yield, performed on a comprehensive analysis approach, and profit farmers are yet to be understood. This study reviewed different experimental studies conducted on soybean (Glycine max (L.) Merr.), cowpea (Vigna unguiculata [L.] Walp), and groundnut (Arachis hypogaea [L.]) to which Rhz inoculants, P supplements, or Rhz + P combination were applied to improve the yield in Ghana. Multiple-step search combinations of published articles and multivariate analysis computing approaches were used to assess the effects of Rhz inoculation, P application, or both application of Rhz and P on yield variation. The random forest (RF) regression model was further employed to quantify the relative importance of various predictor variables on yield. The meta-analysis results showed that cowpea exhibited the highest (61.7%) and groundnut (19.8%) the lowest average yield change. The RF regression model revealed that the combined application of Rhz and P fertilizer (10.5%) and Rhz inoculation alone (7.8%) were the highest explanatory variables to predict yield variation in soybean. The Rhz + P combination, Rhz inoculation, and genotype wang-Kae explained 11.6, 10.02, and 8.04% of yield variability for cowpea, respectively. The yield in the inoculated plants increased by 1.48-, 1.26-, and 1.16-fold when compared to that in the non-inoculated cowpea plants following inoculation with BR 3299, KNUST 1002, and KNUST 1006 strains, respectively. KNUST 1006 strain exhibited the highest yield increase ratio (1.3-fold) in groundnut plants. Inoculants formulation with a viable concentration of 10⁹ cells g^-1 and a minimum inoculum rate of 1.0 × 10⁶ cells seed^-1 achieved the highest average yield change for soybean but not for cowpea and groundnut. The meta-analysis calls for prospective studies to investigate the minimum rate of bacterial cells required for optimum inoculation responses in cowpea and groundnut.

Phosphate-Dependent Regulation of Growth and Stresses Management in Plants

The importance of phosphorus in the regulation of plant growth function is well studied. However, the role of the inorganic phosphate (Pi) molecule in the mitigation of abiotic stresses such as drought, salinity, heavy metal, heat, and acid stresses are poorly understood. We revisited peer-reviewed articles on plant growth characteristics that are phosphorus (P)-dependently regulated under the sufficient-P and low/no-P starvation alone or either combined with one of the mentioned stress. We found that the photosynthesis rate and stomatal conductance decreased under Pi-starved conditions. The total chlorophyll contents were increased in the P-deficient plants, owing to the lack of Pi molecules to sustain the photosynthesis functioning, particularly, the Rubisco and fructose-1,6-bisphosphatase function. The dry biomass of shoots, roots, and P concentrations were significantly reduced under Pi starvation with marketable effects in the cereal than in the legumes. To mitigate P stress, plants activate alternative regulatory pathways, the Pi-dependent glycolysis, and mitochondrial respiration in the cytoplasm. Plants grown under well-Pi supplementation of drought stress exhibited higher dry biomass of shoots than the no-P treated ones. The Pi supply to plants grown under heavy metals stress reduced the metal concentrations in the leaves for the cadmium (Cd) and lead (Pb), but could not prevent them from absorbing heavy metals from soils. To detoxify from heavy metal stress, plants enhance the catalase and ascorbate peroxidase activity that prevents lipid peroxidation in the leaves. The HvPIP and PHO1 genes were over-expressed under both Pi starvation alone and Pi plus drought, or Pi plus salinity stress combination, implying their key roles to mediate the stress mitigations. Agronomy Pi-based interventions to increase Pi at the on-farm levels were discussed. Revisiting the roles of P in growth and its better management in agricultural lands or where P is supplemented as fertilizer could help the plants to survive under abiotic stresses.

Assessing diversity in canopy architecture, photosynthesis, and water-use efficiency in a cowpea magic population

Optimizing crops to improve light absorption and CO2 assimilation throughout the canopy is a proposed strategy to increase yield and meet the needs of a growing population by 2050. Globally, the greatest population increase is expected to occur in Sub-Saharan Africa where large yield gaps currently persist; therefore, it is crucial to develop high-yielding crops adapted to this region. In this study, we screened 50 cowpea (Vigna unguiculata (L.) Walp) genotypes from the multi-parent advanced generation inter-cross (MAGIC) population for canopy architectural traits, canopy photosynthesis, and water-use efficiency using a canopy gas exchange chamber in order to improve our understanding of the relationships among those traits. Canopy architecture contributed to 38.6% of the variance observed in canopy photosynthesis. The results suggest that the light environment within the canopy was a limiting factor for canopy CO2 assimilation. Traits favoring greater exposure of leaf area to light such as the width of the canopy relative to the total leaf area were associated with greater canopy photosynthesis, especially in canopies with high biomass. Canopy water-use efficiency was highly determined by canopy photosynthetic activity and therefore canopy architecture, which indicates that optimizing the canopy will also contribute to improving canopy water-use efficiency. We discuss different breeding strategies for future programs aimed at the improvement of cowpea yield for the Sub-Saharan African region. We show that breeding for high biomass will not optimize canopy CO2 assimilation and suggest that selection should include multiple canopy traits to improve light penetration.

Developing the role of legumes in West Africa under climate change

West Africa is faced with significant challenges from climate change, including parts of the region becoming hotter with more variable rainfall. The Sahelian region in particular is already subject to severe droughts. To address this better adapted crop varieties (such as for cowpea) are clearly a central element, a complementary one is a greater use of resilient alternative crops especially underutilized legumes particularly Bambara groundnut, African yam bean, winged bean and Kersting's groundnut. Genetic diversity of these crops conserved in genebanks and farmer's field provides an opportunity to exploit climate resilient traits using cutting-edge genomic tools and to use genomics-assisted breeding to accelerate genetic gains in combination of rapid cycle breeding strategy to develop climate-resilient cultivars for sub-Saharan Africa.

Dry-Caribbean Bacillus spp. Strains Ameliorate Drought Stress in Maize by a Strain-Specific Antioxidant Response Modulation

Drought is a global problem for crop productivity. Therefore, the objective of this research was to evaluate five dry-Caribbean Bacillus spp. strains in drought stress amelioration in maize plants. Maize seeds were single-strain inoculated and sown in pots under greenhouse conditions. After 12 days, plants were subjected to 33 days of drought conditions, i.e., 30% of soil field capacity, and then collected to measure leaf and root dry biomass, plant height, antioxidant enzymes, proline accumulation, and P⁺, Ca²⁺, and K⁺ uptake. Results correlated drought stress amelioration with the inoculation of Bacillus spp. strains XT13, XT38 and XT110. Inoculated plants showed increases in dry biomass, plant height, and K⁺ and P⁺ uptake. The overall maize antioxidant response to bacterial inoculation under drought stress showed dependence on proline accumulation and decreases in ascorbate peroxidase and glutathione reductase activities. Moreover, results suggest that this stress amelioration is driven by a specific plant-strain correlation observed in antioxidant response changes in inoculated plants under stress. Also, there is a complex integration of several mechanisms, including plant growth-promotion traits and nutrient uptake. Hence, the use of dry-Caribbean plant growth-promoting Bacillus strains represents an important biotechnological approach to enhance crop productivity in arid and semi-arid environments.

Arbuscular mycorrhizal fungi modulates dynamics tolerance expression to mitigate drought stress in Ephedra foliata Boiss

Arbuscular mycorrhizal fungi (AMF) are one of the most important drivers of soil ecosystem dynamics. AMF have the potential to improve plant growth and development by modulating key hormonal pathways, which result in decreasing the adverse impact of abiotic stress, such as drought. Pot experiments were conducted in this study to investigate the ability of AMF to ameliorate the adverse impact of drought in Ephedra foliate. Non-inoculated AMF E. foliate (Ef) plants, exhibited reduced growth in response to drought stress with a concomitant lowering of chlorophyll pigments, relative to non-stressed and AMF inoculated plant. AMF inoculated E. foliate showed improved nitrogen metabolism by positively regulating nitrate and nitrite reductase activity which results in greater ammonium availability for the synthesis of amino acids. Inoculation with AMF also increased antioxidant enzyme activity, ascorbic acid contents, and reduction in glutathione level. This resulted in significant amelioration of oxidative damage to plant membranes by restricting the excess generation of reactive oxygen species (ROS), such as hydrogen peroxide. Greater content of proline, glucose, and total soluble protein in AMF-inoculated plants provided further benefit to E. foliate plants and their ability to withstand drought stress, and also evident by a greater level of sucrose phosphate synthase activity. AMF significantly enhanced the uptake of essential nutrients like K, Mg, and Ca. Importantly, higher concentrations of plant hormones, including indole acetic acid (IAA), indole butyric acid (IBA), gibberellic acid (GA), and abscisic acid (ABA), were maintained in AMF-inoculated Ef plants. AMF inoculation also boosted phosphorous metabolism by increasing alkaline and acid phosphatase enzyme activity. In summary, AMF-inoculation of Ef plants significantly reduced the deleterious effect of drought stress by up-regulating the antioxidant defense system, synthesis of osmolytes, and maintaining phytohormone levels.

Divergent metabolic adjustments in nodules are indispensable for efficient N2 fixation of soybean under phosphate stress

The main objective of the present study was to characterize the symbiotic N2 fixation (SNF) capacity and to elucidate the underlying mechanisms for low-Pi acclimation in soybean plants grown in association with two Bradyrhizobium diazoefficiens strains which differ in SNF capacity (USDA110 vs. CB1809). In comparison with the USDA110-soybean, the CB1809-soybean association revealed a greater SNF capacity in response to Pi starvation, as evidenced by relative higher plant growth and higher expression levels of the nifHDK genes. This enhanced Pi acclimation was partially related to the efficient utilization to the overall carbon (C) budget of symbiosis in the CB1809-induced nodules compared with that of the USDA110-induced nodules under low-Pi provision. In contrast, the USDA110-induced nodules favored other metabolic acclimation mechanisms that expend substantial C cost, and consequently cause negative implications on nodule C expenditure during low-Pi conditions. Fatty acids, phytosterols and secondary metabolites are characterized among the metabolic pathways involved in nodule acclimation under Pi starvation. While USDA110-soybean association performed better under Pi sufficiency, it is very likely that the CB1809-soybean association is better acclimatized to cope with Pi deficiency owing to the more effective functional plasticity and lower C cost associated with these nodular metabolic arrangements.

Influence of fungicides on activities of enzymes of phenolic metabolism in the early stages of formation and functioning of soybean symbiotic apparatus

We studied the effect of complex seed treatment with fungicides and rhizobium culture on the activity of phenolic metabolism enzymes – polyphenol oxidase and guaiacol peroxidase in the early stages of the formation and functioning of various symbiotic systems Glycine max – Bradyrhizobium japonicum. In the research we used microbiological, physiological, biochemical methods, gas chromatography and spectrophotometry. The objects of the study were selected symbiotic systems formed with the participation of soybean (Glycine max (L.) Merr.), Diamond variety, strains Bradyrhizobium japonicum 634b (active, virulent) and 604k (inactive, highly virulent) and fungicides Maxim XL 035 PS (fludioxonil, 25 g/L, metalaxyl, 10 g/L), and Standak Top (fipronil, 250 g/L, thiophanate methyl, 225 g/L, piraclostrobin, 25 g/L). Before sowing, the seeds of soybean were treated with solutions of fungicides, calculated on the basis of one rate of expenditure of the active substance of each preparation indicated by the producer per ton of seed. One part of the seeds treated with fungicides was inoculated with rhizobium culture for 1 h (the titre of bacteria was 108 cells in 1 ml). The other part of the fungicide-treated seeds was not inoculated by rhizobium culture. As a result of the research, it was revealed that an effective symbiotic system formed with the participation of soybean plants and the active strain rhizobia 634b is characterized by a high level of polyphenol oxidase activity and low guaiacol peroxidase in roots and root nodules in the stages of second and third true leaves. Such changes in the activity of enzymes occurred along with the formation of nodules which actively fixed the molecular nitrogen of the atmosphere. An ineffective symbiotic system (strain 604k) is characterized by an elevated level of polyphenol oxidase activity in the roots and guaiacol peroxidase in the root nodules, which is accompanied by activation of the process of nodulation. Treatment of soybean seeds with fungicides in an effective symbiotic system leads to a change in the activity of the enzymes of the phenolic metabolism, which induced adaptive changes in plant metabolism and growth of nitrogenase activity of the root nodules. The recorded changes in the activity of both enzymes for the action of fungicides in the ineffective symbiotic system can be considered as a kind of response of the plant to the treatment and were observed along with the reduction of the processes of nodulation into the stage of the third true leaf.

Leaf Gas Exchange, Plant Water Relations and Water Use Efficiency of Vigna Unguiculata L. Walp. Inoculated with Rhizobia under Different Soil Water Regimes

Impact of soil water regimes on physiological responses and water use efficiency (WUE) for Vigna unguiculata L. Walp. (cowpea) inoculated with rhizobia still remains implicit. Therefore, the goal of the current study was to examine the leaf gas exchange, abscisic acid (ABA) and hydraulic signaling, WUE and carbon and oxygen isotopic compositions (δ13C and δ18O) of cowpea under different soil water levels. The treatments included soil water regimes at three levels (90%, 70%, and 50% of soil water holding capacity (SWHC)) and two inoculation forms (inoculated and non-inoculated with rhizobia). The results showed that across the inoculation treatments, reduced soil water regimes depressed both stomatal conductance (gs) and photosynthesis (An) of the leaves, nonetheless, the decrease of gs was more pronounced compared with the reduction in An. Consequently, the intrinsic water use efficiency (WUEi) was improved in the treatments under decreased soil water conditions. Plant WUE was also improved when soil water contents decreased as exemplified by the increased leaf δ13C and δ18O, indicating the enhanced plant WUE was mainly attributed to the decrease of gs. Significant interactions between soil water regimes and rhizobia treatments for root water potential (RWP), leaf water potential (LWP), and gs were found due to the different responses of rhizobia to varied soil water regimes. Inoculation could improve plant water status and gs under 70% and 90% SWHC compared to 50% SWHC with negative effect from rhizobia. A moderate soil water regime is suggested for cowpea production in terms of high WUE with a minor biomass reduction.

Arbuscular mycorrhizal fungi and biochar improves drought tolerance in chickpea

Arbuscular mycorrhizal fungi (AMF) inoculation and biochar amendment has been reported to improve growth of several crop plants however their role in stress amelioration individually as well as in combination has not been worked out. This experiment was conducted to evaluate the application of AMF and biochar on the performance of chickpea under drought stress. The treatments included the individual as well as combined treatment of AMF and biochar to drought stressed and normal chickpea plants. Plants inoculation improved growth in terms of shoot and root length, leaf area and number of branches which was observed to show a steep decline due to drought stress. Drought declined the AMF colonization potential though biochar amendment ameliorated the negative effects of drought significantly by improving the spore population, number of mycelium, vesicle and arbuscules and the percentage of colonization as well. Increased chlorophyll synthesis in biochar and AMF treated plants was obvious, which lead to significant enhancement in the net photosynthetic efficiency. Drought stress also declined the relative water content (RWC) and membrane stability index (MSI), while treatment of biochar and AMF either individually or in combination mitigated the deleterious effects to considerable extent and caused a significant enhancement in RWC and MSI under normal conditions. Amendments with biochar and AMF inoculation increased the nitrogen fixation attributes including the number and weight of nodules, leghemoglobin content and activity of nitrate reductase enzyme leading to greater uptake and assimilation of nitrogen in them when compared to drought stressed plants. Drought stressed chickpea plants exhibited considerable reduction in uptake of nitrogen and phosphorous which was ameliorated by biochar and AMF treatments. It could be suggested that increase in growth and physiological attributes in chickpea due to biochar amendments and AMF inoculation under drought stress were plausibly due to their involvement in nitrogen and phosphorous uptake, chlorophyll synthesis and photosynthesis.

Genetic Analysis and Mapping of QTLs for Soybean Biological Nitrogen Fixation Traits Under Varied Field Conditions

Soybean is an important economic and green manure crop that is widely used in intercropping and rotation systems due to its high biological nitrogen fixation (BNF) capacity and the resulting reduction in N fertilization. However, the genetic mechanisms underlying soybean BNF are largely unknown. Here, two soybean parent genotypes contrasting in BNF traits and 168 F_9:11 recombinant inbred lines (RILs) were evaluated under four conditions in the field. The parent FC1 always produced more big nodules, yet fewer nodules in total than the parent FC2 in the field. Furthermore, nodulation in FC1 was more responsive to environmental changes than that in FC2. Broad-sense heritability (h² _b ) for all BNF traits varied from 0.48 to 0.87, which suggests that variation in the observed BNF traits was primarily determined by genotype. Moreover, two new QTLs for BNF traits, qBNF-16 and qBNF-17, were identified in this study. The qBNF-16 locus was detected under all of the four tested conditions, where it explained 15.9-59.0% of phenotypic variation with LOD values of 6.31-32.5. Meanwhile qBNF-17 explained 12.6-18.6% of observed variation with LOD values of 4.93-7.51. Genotype group analysis indicated that the FC1 genotype of qBNF-16 primarily affected nodule size (NS), while the FC2 genotype of qBNF-16 promoted nodule number (NN). On the other hand, the FC1 genotype of qBNF-17 influenced NN and the FC2 genotype of qBNF-17 impacted NS. The results on the whole suggest that these two QTLs might be valuable markers for breeding elite soybean varieties with high BNF capacities.

Mycorrhizal fungal community structure in tropical humid soils under fallow and cropping conditions

Little is known to what extent soil biota, in particular, the mycorrhizae are altered through different fallow durations/types in tropical soils. We found that soil-N, -C, -Al, -K and -Ca contents significantly differed due to the fallow durations/types. Subsequently, the effects of fallow types and soil depths on the diversity, species richness and community structure of arbuscular mycorrhizal (AM) fungi were examined. A higher AM species richness was identified in the cropping than in forest fallow fields, suggesting a positive cropping feedback on the AM community composition. Distribution of the AM species was positively related to soil properties, specifically soil-pH, and soil-Pi, -Ca and -Mg contents. The soil properties conjointly accounted for 78.5% of explained variation in the AM community composition, signifying that the main factors altering the community structure under different fallow and cropping systems were the soil properties. Among the soil chemical characteristics, the soil-pH disclosed a significant explained variation in the AM community composition in the topsoil layer under the short fallow. Structural modeling equation to understand multiple predictive pathways that connect soil properties, fallow practices and AM community structures indicated that soil-C, -N and -Ca contents were highlighted as important factors influencing the AM community compositions.