Intercropping is a common cropping practice that takes advantage of plant diversity and plant complementarity to increase land-use efficiency. Biofertilizers centered around arbuscular mycorrhizal fungi (AMF) and plant growth promoting rhizobacteria (PGPR) are supplements to mineral fertilizers well-known for their far-reaching beneficial effects on plants such as increased drought resistance and increased yields. This study tested if the combination of intercropping and biofertilizers can enhance land-use efficiency (overyielding) using staple crops from southern India. Specifically, the role of different combinations of plant species (crop mixtures) and spatial arrangements mediating overyielding in intercropping was tested. Biofertilizer inoculation increased yields in both monocropping and intercropping. In intercropping, grain yield improved by an average of 23% over the control, regardless of the crop mixture or spatial arrangement. Positive crop-type-specific mycorrhizal growth responses (MGR) and overyielding across experimental treatments and sites indicate that combining biofertilizers with intercropping significantly enhances land-use efficiency in the semi-arid tropics. These findings have practical implications for improving the productivity of intercropping systems in dryland agricultural systems, particularly under resource-limited conditions.

Arbuscular mycorrhizal fungi (AMF) are widely known to improve plant and soil health by forming an obligate symbiotic relationship with most terrestrial plants. AMF biofertilizers can significantly reduce the need for synthetic inputs. The contribution of AMF to crop yield enhancement and ecological services is widely documented. Apart from agriculture, AMF applications have also found a significant position in forestry, agroforestry, horticulture, and restoring natural ecosystems. AMF promote soil aggregation, sequester soil C, and improve soil health by modifying the physical and nutritional state of the rhizosphere. Considering soil salinization and heavy metal pollution, AMF could act as bio-ameliorators. The production of AMF biofertilizers is challenging due to their obligate symbiotic nature which requires the presence of actively growing plant roots to complete their life cycle. AMF infectious propagules include arbuscules, spores, vesicles, and hyphae (intraradical and extraradical). Each of these can infect a plant and be used for AMF production. Several methods have been introduced to mass-produce AMF such as hydroponics, aeroponics, substrate-based, on-farm, and in vitro techniques. Substrate-based and on-farm production are simpler, while in vitro method ensures contamination-free inoculum. Hydroponics and aeroponics do not need a substrate but require a complex setup. The mass multiplication of AMF is widely attempted across the globe, but its success is a determinant of numerous factors that are often overlooked. This chapter tries to elucidate the various AMF inoculum production processes and their influencing elements. In addition, attempts have been made to comprehend how AMF inoculum could be adapted to a variety of crops and soil types to increase the benefits received from AMF in sustainable agriculture.

Ecological intensification (EI) provides an important and increasingly adopted pathway for achieving more sustainable agricultural systems. However, the implementation and success of on-farm EI practices may vary depending on landscape context and local management practices. We evaluated how EI interventions, including two different agricultural input regimes (high or low use of synthetic pesticides and fertilizers) and floral border crops, affected local natural enemy biodiversity, pest abundance and crop yield, and how this was influenced by the surrounding landscape context across 12 rice fields on smallholder farms in Puducherry, India. Reducing agricultural inputs positively impacted the overall natural enemy assemblage; however, responses to landscape factors varied. For example, coccinellid beetles were negatively correlated with higher densities of field edges (landscape configuration). In contrast, spiders, the most abundant group surveyed, were not significantly influenced by any landscape metric. Furthermore, pest abundance was greatest in fields with reduced inputs but only at sites where floral border crops were not present. Mean rice grain yield was lower across low-input sites compared with high-input sites and floral border crops had opposing effects across high- and low-input sites. At low-input sites, mean yields were 33% higher where floral border crops were present. At high-input sites, the presence of floral border crops was correlated with a lower mean yield (16%). These findings show that ecological intensification practices can benefit smallholder crop systems but highlight the need to account for variations in landscape context and local management practices for developing effective sustainable management practices.

Millets, also known as the “future food”, provide a viable option for combating malnutrition and mitigating climate change. The rhizosphere of millets accommodates numerous microbial communities that improve plant nutrient acquisition, growth, and productivity and also protect from abiotic and biotic stresses. Exploiting the millet rhizomicrobiome will improve soil health and plant nutrition, reduce the need for environmentally toxic synthetic fertilizers, and offer a more affordable alternative. The knowledge about the dominant microbial groups will also help in devising strategies for developing inoculum well-adapted to millets. The key microbial groups in the millet rhizosphere and their effects on plant growth, stress tolerance, and soil health have been described in this chapter. In addition, we have provided an overview of the methods used to examine rhizosphere microbial communities.

Intercropping is a sustainable agroecological tool known to provide multiple benefits to farmers. Several studies have shown that arbuscular mycorrhizal fungi (AMF) play a key role for the improved grain yields in intercropping systems through facilitative nutrient and water uptake via the common mycorrhizal network (CMN), yet little is known on the rate of hyphal spread. Here we hypothesized that AMF species differ in the rate of extraradical hyphae to spread from one plant to another, thereby affecting the growth of the intercropped plants. To test our hypothesis, we established experimental microcosms in the greenhouse, in which one pigeon pea (Cajanus cajan) and two finger millet (Eleusine coracana) plantlets were kept in separate pots, connected by soil bridges of 5 or 12 cm length, inaccessible to roots but accessible to fungal hyphae. The pigeon pea plants were pre-inoculated with Claroideoglomus etunicatum, Rhizophagus fasciculatus or Rhizophagus irregularis. All three AMF species led to a strong growth promotion compared to uninoculated control of the short microcosms and more than doubled the biomass of pigeon pea. The biomass as well the phosphorus content of finger millets connected by AMF to the pigeon pea differed with the length of the soil bridge and the species of AMF. By applying 15N isotopes to the soil of pigeon pea pots we revealed that in both lengths of the microcosms R. fasciculatus and C. etunicatum transported nitrogen from pigeon pea to finger millet across distances of up to 12 cm but R. irregularis did not. Furthermore, by destructive sampling, we estimated a hyphal spread of 4.1 mm d-1 by C. etunicatum across a 12 cm soil bridge. We conclude that the row distance between the crops and the choice of AMF species play a crucial role for the application of AMF as biofertilizer.

Intercropping is a well-established practice to enhance the yield in low-input agriculture, and beneficial microbes such as arbuscular mycorrhizal fungi (AMF) combined with plant growth promoting rhizobacteria are being used as an effective and sustainable measure to improve yields. In this study, we tested if biofertilizers can not only enhance the yield of crops in monoculture as has previously been demonstrated but can also enhance the yield of intercropping systems. We hypothesized that because AMF can form common mycorrhizal networks (CMN) that can transfer nutrients and water between different plant species, biofertilization can balance belowground competition between crop species and promote thus overall yields in intercropping systems. In our study, we used a pigeon pea (PP)—finger millet (FM) intercropping system that we grew for two consecutive growing seasons (2016/17 and 2017/18) at two contrasting sites in Bengaluru and Kolli Hills, India. We also tested if the spatial arrangement (i.e., different arrangement of component plants with similar plant density in intercropping system) of intercropped plants, using either a row-wise or a mosaic design, influences the effect of biofertilizers on yield and water relations of the PP-FM intercropping system. Our results demonstrate that intercropping can improve the straw and grain yield of PP and FM compared to the respective monocultures and that intercropping effects vary depending on the site characteristic such as climate and soil type. The spatial arrangement of component plants affected the total, straw, and grain biomass in intercropping treatments, but this effect also varied across sites. Most importantly, the results from the 2017/18 growing season clearly demonstrated a positive effect of biofertilizer on biomass yield, and this effect was irrespective of site, spatial arrangement, mixed or monoculture. Our study therefore shows that yield increase in intercropping systems can further be improved through the application of biofertilizers.

Pigeon pea (Cajanus cajan) and finger millet (Eleusine coracana) are staple food crops for millions of the rural population in Asia and Africa. We tested, in field trials over three consecutive seasons at two sites in India, an intercropping and biofertilization scheme to boost their yields under low-input conditions. Pigeon pea seedlings were raised during the dry season and transplanted row-wise into fields of finger millet, and arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (Pseudomonas) were added alone or in combination to both pigeon pea and finger millet. Our major findings are (i) effects of the biofertilizers were particularly pronounced at the site of low fertility; (ii) dual inoculation of AMF+PGPR to finger millet and pigeon pea crops showed increased grain yields more effectively than single inoculation; (iii) the combined grain yields of finger millet and pigeon pea in intercropping increased up to +128% due to the biofertilizer application; (iv) compared to direct sowing, the transplanting system of pigeon pea increased their average grain yield up to 267% across site, and the yield gains due to biofertilization and the transplanting system were additive. These technologies thus offer a tool box for sustainable yield improvement of pigeon pea and finger millet.

Bioirrigation has been defined as the transfer of hydraulically lifted water by a deep-rooted plant to a neighbouring shallow-rooted plant which cannot access deep soil moisture. In this study, we tested if facilitative effects of bioirrigation or the competition for water dominate the interaction of two intercropped plants-deep-rooted pigeon pea (PP) and shallow-rooted finger millet (FM) before and during a drought. Additionally, we tested how the presence of a common mycorrhizal network (CMN) affects the balance between facilitative (i.e. bioirrigation) and competitive interactions between two intercropping species. Our results show that PP can indeed promote the water relations of FM during a drought event. Specifically, stomatal conductance in FM controls dropped to low values of 27.1 to 33.6 mmol m-2s-1, while FM in intercropping treatments were able to maintain its stomatal conductance at 60 mmol m-2s-1. In addition, the presence of PP reduced the drought-induced foliar damage and mortality of FM. The observed facilitative effects of PP on FM were partially enhanced by the presence of a CMN. In contrast to the facilitative effects under drought, PP exerted strong competitive effects on FM before the onset of drought. This hindered growth and biomass production of FM when intercropped with PP, an effect that was even enhanced in the presence of a CMN. The results from our study thus indicate that in intercropping, deep-rooted plants may act as "bioirrigators" for shallow-rooted crops and that a CMN can promote these facilitative effects. However, the interspecific competition between the intercropped plants under conditions of abundant moisture supply can be strong and are enhanced by the presence of a CMN. In more general terms, our study shows that the extent by which the antagonistic effects of facilitation and competition are expressed in an intercropping system strongly depends on the availability of resources, which in the case of the present study was water and the presence of biotic interactions (i.e. the presence of a CMN).

Drought is a critical factor limiting the productivity of legumes worldwide. Legumes can enter into a unique tripartite symbiotic relationship with root-nodulating bacteria of generaRhizobium,Bradyrhizobium, orSinorhizobiumand colonization by arbuscular mycorrhizal fungi (AMF). Rhizobial symbiosis provides nitrogen necessary for growth. AMF symbiosis enhances uptake of diffusion-limited nutrients such as P, Zn, Cu, etc., and also water from the soilviaplant-associated fungal hyphae. Rhizobial and AMF symbioses can act synergistically in promoting plant growth and fitness, resulting in overall yield benefits under drought stress. One of the approaches that rhizobia use to survive under stress is the accumulation of compatible solutes, or osmolytes, such as trehalose. Trehalose is a non-reducing disaccharide and an osmolyte reported to accumulate in a range of organisms. High accumulation of trehalose in bacteroids during nodulation protects cells and proteins from osmotic shock, desiccation, and heat under drought stress. Manipulation of trehalose cell concentrations has been directly correlated with stress response in plants and other organisms, including AMF. However, the role of this compound in the tripartite symbiotic relationship is not fully explored. This review describes the biological importance and the role of trehalose in the tripartite symbiosis between plants, rhizobia, and AMF. In particular, we review the physiological functions and the molecular investigations of trehalose carried out using omics-based approaches. This review will pave the way for future studies investigating possible metabolic engineering of this biomolecule for enhancing abiotic stress tolerance in plants.

Hydraulically lifted water can be redistributed to a neighbouring plant, a process referred to as “bioirrigation”. Facilitation of bioirrigation by beneficial microbes such as arbuscular mycorrhizal (AM) fungi that form a common mycorrhizal network (CMN) between neighbouring plants has often been suggested but is not yet well explored. In this study, we tested if the presence of a CMN can facilitate the transfer of hydraulically lifted water from pigeon pea (PP) to finger millet (FM) and ameliorate thereby the water relations of the shallow-rooted FM during drought. In a compartmented microcosm set up, PP roots were grown up to the bottom layer of the pot to access the soil moisture. Whereas FM roots were restricted into a shallow compartment, separated through a 21 μm nylon mesh, without access to the moist bottom layer. We applied deuterium labelled water to the bottom layer of the pot to test if PP can perform hydraulic lift (HL) and if hydraulically lifted water is transferred to FM via a CMN. During the drought period we also assessed the water relations of FM to determine if bioirrigation mediated through a CMN can support the water relations of FM. Application of deuterium-enriched water to the moist bottom layer of the microcosms demonstrated the capability of PP to hydraulically lift water to the drier topsoil through an insulation layer of coarse gravel. Only FM plants that were connected to PP via a CMN were able to utilize HL water. As a consequence, FM bioirrigated by PP in the presence of a CMN was able to maintain its water relations during drought conditions and showed higher rates of survival than FM plants in monoculture. Connecting the rhizosphere of two intercropping partners with a CMN can improve the water relations of shallow-rooted crops by bioirrigation. This finding has great potential for reducing drought induced crop yield loss in arid and semi-arid tropics.

The application of microbial inoculants (biofertilizers) is a promising technology for future sustainable farming systems in view of rapidly decreasing phosphorus stocks and the need to more efficiently use available nitrogen (N). Various microbial taxa are currently used as biofertilizers, based on their capacity to access nutrients from fertilizers and soil stocks, to fix atmospheric nitrogen, to improve water uptake or to act as biocontrol agents. Despite the existence of a considerable knowledge on effects of specific taxa of biofertilizers, a comprehensive quantitative assessment of the performance of biofertilizers with different traits such as phosphorus solubilization and N fixation applied to various crops at a global scale is missing. We conducted a meta-analysis to quantify benefits of biofertilizers in terms of yield increase, nitrogen and phosphorus use efficiency, based on 171 peer reviewed publications that met eligibility criteria. Major findings are: (i) the superiority of biofertilizer performance in dry climates over other climatic regions (yield response: dry climate +20.0 ± 1.7%, tropical climate +14.9 ± 1.2%, oceanic climate +10.0 ± 3.7%, continental climate +8.5 ± 2.4%); (ii) meta-regression analyses revealed that yield response due to biofertilizer application was generally small at low soil P levels; efficacy increased along higher soil P levels in the order arbuscular mycorrhizal fungi (AMF), P solubilizers, and N fixers; (iii) meta-regressions showed that the success of inoculation with AMF was greater at low organic matter content and at neutral pH. Our comprehensive analysis provides a basis and guidance for proper choice and application of biofertilizers.

Legume-cereal intercropping is well known in traditional dry land agriculture. Here, we tested whether finger millet, a shallow-rooted cereal, can profit from neighboring pigeon pea, a deep-rooted legume, in the presence of “biofertilization” with arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR), under drought conditions. We conducted a greenhouse experiment using compartmented microcosms. Pigeon pea was grown in a deep compartment with access to a moist substrate layer at the bottom, whereas finger millet was grown in a neighboring shallow compartment, separated by 25-µm nylon mesh, without access to the moist substrate layer. In the presence of a common mycorrhizal network (CMN), with or without PGPR, a drought condition had little negative effect on the biomass production of the finger millet plant whereas in absence of biofertilization, finger millet biomass production was less than half compared to well-watered condition. Biofertilization strongly increased nitrogen and phosphorus uptake by both plants, both under well-watered and drought conditions. In the presence of AMF, both plants also acquired 15N and 33P, offered in a labeling compartment accessible to fungal hyphae but not to roots. Our results show that “biofertilization” with AMF alleviates the negative effects of drought condition on finger millet, indicating that the CMN connecting pigeon pea and finger millet exert clearly a positive influence in this simulated intercropping system.

Drought dramatically reduces crop yield, therefore remains as a major threat to food security.Overcoming drought by crop plants is a complex phenomenonwhere plants find ways mainly through physiological adaptation.However, in nature, the plants rely also on microbes for mitigating the drought effects.Below ground association of plant roots with rhizosphere microorganisms for tolerating drought has been though established earlier, the exact mechanism is being understood only recently.The role of below ground microbes, particularly by the arbuscular mycorrhizal fungi (AMF), in drought tolerance by crop plants is currently a key research topic.The significance and highlights of the recent research as well as the past understanding of mechanisms by which crop plants tolerate drought through association of soil beneficial microbes, particularly with that of the AMF, is discussed in this review.

Pigeon pea and finger millet plants were grown in a pot (21 X 12.8 cm), and the pot was filled in layers with the different material (as shown in figure 1). The top compartment for finger millet was made with a nylon mesh (16 μm pore diameter) that allows mycorrihza to grow through the mesh but restricts the root to pass through. The next layer of gravel (6 cm above bottom) prevent rise of water to the top through capillary rise, the next layers of medium and fine sand (2 cm) help in retaining the moisture for long time in the top layer (terragreen plus sand). The Drought period started from week 13th and during drought period pots were watered by immersing the bottom 5 cm into the water for 15 minute and additional 10 ml of water was added to the top layer. Pots were watered at the interval of 2 days, and the experiment was continued till the end of 19th week. Photosynthesis rate and stomatal conductance were measured after 24 and 48 hours of watering.

•Monitoring of non-target effects of bioinoculants in Cajanus cajan's rhizosphere.•Individual as well as combination of bioinoculants employed.•Cultivation-dependent and -independent approaches to target microorganisms.•Increased abundance of PGPR observed in treated plants.•Non-target effects evident by ARISA profiles of treated and control plants.

Plants commonly live in a symbiotic association with arbuscular mycorrhizal fungi (AMF). They invest photosynthetic products to feed their fungal partners, which, in return, provide mineral nutrients foraged in the soil by their intricate hyphal networks. Intriguingly, AMF can link neighboring plants, forming common mycorrhizal networks (CMNs). What are the terms of trade in such CMNs between plants and their shared fungal partners? To address this question, we set up microcosms containing a pair of test plants, interlinked by a CMN of Glomus intraradices or Glomus mosseae. The plants were flax (Linum usitatissimum; a C(3) plant) and sorghum (Sorghum bicolor; a C(4) plant), which display distinctly different (13)C/(12)C isotope compositions. This allowed us to differentially assess the carbon investment of the two plants into the CMN through stable isotope tracing. In parallel, we determined the plants' "return of investment" (i.e. the acquisition of nutrients via CMN) using (15)N and (33)P as tracers. Depending on the AMF species, we found a strong asymmetry in the terms of trade: flax invested little carbon but gained up to 94% of the nitrogen and phosphorus provided by the CMN, which highly facilitated growth, whereas the neighboring sorghum invested massive amounts of carbon with little return but was barely affected in growth. Overall biomass production in the mixed culture surpassed the mean of the two monocultures. Thus, CMNs may contribute to interplant facilitation and the productivity boosts often found with intercropping compared with conventional monocropping.

ABSTRACT Plant growth-promoting rhizobacterial (PGPR) strains R62 and R81 have previously been isolated and characterized as part of the Indo-Swiss Collaboration in Biotechnology. Here we present the draft genome sequences of these two PGPR strains, with the aim of unraveling the mechanisms behind their ability to promote wheat growth.

Arbuscular mycorrhizal fungi (AMF) are important symbionts of plants that improve plant nutrient acquisition and promote plant diversity. Although within-species genetic differences among AMF have been shown to differentially affect plant growth, very little is actually known about the degree of genetic diversity in AMF populations. This is largely because of difficulties in isolation and cultivation of the fungi in a clean system allowing reliable genotyping to be performed. A population of the arbuscular mycorrhizal fungus Glomus intraradices growing in an in vitro cultivation system was studied using newly developed simple sequence repeat (SSR), nuclear gene intron and mitochondrial ribosomal gene intron markers. The markers revealed a strong differentiation at the nuclear and mitochondrial level among isolates. Genotypes were nonrandomly distributed among four plots showing genetic subdivisions in the field. Meanwhile, identical genotypes were found in geographically distant locations. AMF genotypes showed significant preferences to different host plant species (Glycine max, Helianthus annuus and Allium porrum) used before the fungal in vitro culture establishment. Host plants in a field could provide a heterogeneous environment favouring certain genotypes. Such preferences may partly explain within-population patterns of genetic diversity.