Diversity and function of soybean rhizosphere microbiome under nature farming.

Nature farming is a farming system that entails cultivating crops without using chemical fertilizers and pesticides. The present study investigated the bacterial and fungal communities in the rhizosphere of soybean grown in conventional and nature farming soils using wild-type and non-nodulating mutant soybean. The effect of soil fumigant was also analyzed to reveal its perturbation of microbial communities and subsequent effects on the growth of soybean. Overall, the wild-type soybean exhibited a better growth index compared to mutant soybean and especially in nature farming. Nodulation and arbuscular mycorrhiza (AM) fungi colonization were higher in plants under nature farming than in conventionally managed soil; however, fumigation drastically affected these symbioses with greater impacts on plants in nature farming soil. The rhizosphere microbiome diversity in nature farming was higher than that in conventional farming for both cultivars. However, the diversity was significantly decreased after fumigation treatment with a greater impact on nature farming. Principal coordinate analysis revealed that nature farming and conventional farming soil harbored distinct microbial communities and that soil fumigation significantly altered the communities in nature farming soils but not in conventional farming soils. Intriguingly, some beneficial microbial taxa related to plant growth and health, including Rhizobium, Streptomyces, and Burkholderia, were found as distinct microbes in the nature farming soil but were selectively bleached by fumigant treatment. Network analysis revealed a highly complex microbial network with high taxa connectivity observed under nature farming soil than in conventional soil; however, fumigation strongly broke it. Overall, the results highlighted that nature farming embraced higher microbial diversity and the abundance of beneficial soil microbes with a complex and interconnected network structure, and also demonstrated the underlying resilience of the microbial community to environmental perturbations, which is critical under nature farming where chemical fertilizers and pesticides are not applied.

Exogenous nitric oxide promotes salinity tolerance in plants: A meta-analysis.

Nitric oxide (NO) has received much attention since it can boost plant defense mechanisms, and plenty of studies have shown that exogenous NO improves salinity tolerance in plants. However, because of the wide range of experimental settings, it is difficult to assess the administration of optimal dosages, frequency, timing, and method of application and the overall favorable effects of NO on growth and yield improvements. Therefore, we conducted a meta-analysis to reveal the exact physiological and biochemical mechanisms and to understand the influence of plant-related or method-related factors on NO-mediated salt tolerance. Exogenous application of NO significantly influenced biomass accumulation, growth, and yield irrespective of salinity stress. According to this analysis, seed priming and foliar pre-treatment were the most effective methods of NO application to plants. Moreover, one-time and regular intervals of NO treatment were more beneficial for plant growth. The optimum concentration of NO ranges from 0.1 to 0.2 mM, and it alleviates salinity stress up to 150 mM NaCl. Furthermore, the beneficial effect of NO treatment was more pronounced as salinity stress was prolonged (>21 days). This meta-analysis showed that NO supplementation was significantly applicable at germination and seedling stages. Interestingly, exogenous NO treatment boosted plant growth most efficiently in dicots. This meta-analysis showed that exogenous NO alleviates salt-induced oxidative damage and improves plant growth and yield potential by regulating osmotic balance, mineral homeostasis, photosynthetic machinery, the metabolism of reactive oxygen species, and the antioxidant defense mechanism. Our analysis pointed out several research gaps, such as lipid metabolism regulation, reproductive stage performance, C4 plant responses, field-level yield impact, and economic profitability of farmers in response to exogenous NO, which need to be evaluated in the subsequent investigation.

Microbiome and pathobiome analyses reveal changes in community structure by foliar pathogen infection in rice.

Increasing evidence suggests that the plant rhizosphere may recruit beneficial microbes to suppress soil-borne pathogens, but microbiome assembly due to foliar pathogen infection and ecological mechanisms that govern microbiome assembly and functions in the diseased host are not fully understood. To provide a comprehensive view of the rice-associated microbiome, we compared bacterial and fungal communities of healthy rice and those infected with Magnaporthe oryzae, the causal agent of blast disease. We found that the soil had a greater diversity of bacterial and fungal communities than plant endospheric communities. There was no significant dysbiosis of bacterial and fungal microbiome diversity due to disease, but it caused a substantial alteration of bacterial community structure in the root and rhizosphere compartments. The pathobiome analysis showed that the microbiome community structure of leaf and grain tissues was changed markedly at the pathogen infection site, although the alpha diversity did not change. Correspondingly, the relative abundances of some bacteria and fungi were clearly altered in symptomatic tissues. We noted an increase in Rhizobium bacteria and a decline of Tylospora, Clohesyomyces, and Penicillium fungi in the symptomatic leaf and grain tissues from both locations. According to the inferred microbial network, several direct interactions between M. oryzae and other microbes were identified. The majority of edges in the interaction network were positive in diseased samples; contrastingly, the number of edges was much lower in the healthy samples. With source tracking analysis, we observed a sharp contrast in the source of root endosphere bacteria due to Magnaporthe infection. Whereas the majority (71%) of healthy root bacteria could be tracked from the soil, only a very small portion (17%) could be tracked from the soil for diseased samples. These results advanced our understanding and provided potential ideas and a theoretical basis for studying pathobiome and exploiting the microbiome for sustainable agriculture.

Microbe-Mediated Thermotolerance in Plants and Pertinent Mechanisms- A Meta-Analysis and Review.

Microbial symbionts can mediate plant stress responses by enhancing thermal tolerance, but less attention has been paid to measuring these effects across plant-microbe studies. We performed a meta-analysis of published studies as well as discussed with relevant literature to determine how the symbionts influence plant responses under non-stressed versus thermal-stressed conditions. As compared to non-inoculated plants, inoculated plants had significantly higher biomass and photosynthesis under heat stress conditions. A significantly decreased accumulation of malondialdehyde (MDA) and hydrogen peroxide (H2O2) indicated a lower oxidation level in the colonized plants, which was also correlated with the higher activity of catalase, peroxidase, glutathione reductase enzymes due to microbial colonization under heat stress. However, the activity of superoxide dismutase, ascorbate oxidase, ascorbate peroxidase, and proline were variable. Our meta-analysis revealed that microbial colonization influenced plant growth and physiology, but their effects were more noticeable when their host plants were exposed to high-temperature stress than when they grew under ambient temperature conditions. We discussed the mechanisms of microbial conferred plant thermotolerance, including at the molecular level based on the available literature. Further, we highlighted and proposed future directions toward exploring the effects of symbionts on the heat tolerances of plants for their implications in sustainable agricultural production.

Mineral nutrient content of infected plants and allied soils provide insight into wheat blast epidemics.

Wheat is the second-largest cereal crop in Bangladesh and plays an essential role in ensuring the country's food security. Since 2016, there has been a severe epidemic of wheat blast disease in Bangladesh. This research investigated the nutritional context of wheat blast epidemics by analyzing the infected plants and allied soils. We collected blast-infected wheat plants and allied soil samples from six different severely infected regions of the Meherpur district situated in the western part of Bangladesh. The incidence and severity of wheat blast disease in the sampling fields ranged from 84.78 - 95.11% and 82.06-92.19%, respectively. Among the investigated mineral nutrients in plant samples, the concentrations of sulfur (S), calcium (Ca), magnesium (Mg), iron (Fe) and manganese (Mn) were within the acceptable range of the reference values. In contrast, 50% of the plant samples had insufficient phosphorus (P) concentrations, while others were within the critical range. The potassium (K) and copper (Cu) concentrations in more than 33.5% of plants were within the deficient range. The Si concentrations in half of the tested plant samples were below the acceptable level. However, the boron (B) concentration of around 50% of samples was within the toxic range. The total K, Ca, Zn, Fe, Mn, and Cu concentrations of the soils were lower than the reference values. Based on the interpretation of the available soil test values, the concentrations of S, Fe, Mn, and B in most samples were very low. The concentrations of available P, K, Ca, Mg, Zn and Cu in soil samples were higher than the critical limit. There was a negative relationship between K, S, Ca, Mg, Na and Si concentrations with blast incidence and severity. Therefore, this research suggests that certain plant nutrients such as P, K, Cu, B and Si play a vital role in the wheat blast disease epidemic.

Leaf Bleaching in Rice: A New Disease in Vietnam Caused by Methylobacterium indicum, Its Genomic Characterization and the Development of a Suitable Detection Technique.

A new disease in rice that is characterized by leaf bleaching was recently identified in some fields in the Mekong Delta region of Vietnam. The present study was the first to isolate and identify the pathogen of this disease. We confirmed that leaf bleaching symptoms were due to infection with Methylobacterium indicum bacteria using molecular biology approaches. A full-length genome analysis of pathogenic Methylobacterium strain VL1 revealed that it comprises a single chromosome and six plasmids, with a total size of 7.05| |Mbp and GC content of 70.5%. The genomic features of VL1 were similar to those of the non-pathogenic M. indicum strain SE2.11T; however, VL1 possessed additional unique genes, including those related to homoserine lactone biosynthesis. We established a loop-mediated isothermal amplification (LAMP) assay using the unique sequences of VL1 as target sequences for the rapid and simple detection of pathogenic M. indicum strains. Our initial evaluation demonstrated that the LAMP assay successfully distinguished between pathogenic and non-pathogenic strains infecting rice plants in a rapid and sensitive manner. The present results provide insights into the pathogenesis and development of control measures for novel rice diseases.

Plant Salinity Tolerance Conferred by Arbuscular Mycorrhizal Fungi and Associated Mechanisms: A Meta-Analysis.

Soil salinity often hinders plant productivity in both natural and agricultural settings. Arbuscular mycorrhizal fungal (AMF) symbionts can mediate plant stress responses by enhancing salinity tolerance, but less attention has been devoted to measuring these effects across plant-AMF studies. We performed a meta-analysis of published studies to determine how AMF symbionts influence plant responses under non-stressed vs. salt-stressed conditions. Compared to non-AMF plants, AMF plants had significantly higher shoot and root biomass (p < 0.0001) both under non-stressed conditions and in the presence of varying levels of NaCl salinity in soil, and the differences became more prominent as the salinity stress increased. Categorical analyses revealed that the accumulation of plant shoot and root biomass was influenced by various factors, such as the host life cycle and lifestyle, the fungal group, and the duration of the AMF and salinity treatments. More specifically, the effect of Funneliformis on plant shoot biomass was more prominent as the salinity level increased. Additionally, under stress, AMF increased shoot biomass more on plants that are dicots, plants that have nodulation capacity and plants that use the C3 plant photosynthetic pathway. When plants experienced short-term stress (<2 weeks), the effect of AMF was not apparent, but under longer-term stress (>4 weeks), AMF had a distinct effect on the plant response. For the first time, we observed significant phylogenetic signals in plants and mycorrhizal species in terms of their shoot biomass response to moderate levels of salinity stress, i.e., closely related plants had more similar responses, and closely related mycorrhizal species had similar effects than distantly related species. In contrast, the root biomass accumulation trait was related to fungal phylogeny only under non-stressed conditions and not under stressed conditions. Additionally, the influence of AMF on plant biomass was found to be unrelated to plant phylogeny. In line with the greater biomass accumulation in AMF plants, AMF improved the water status, photosynthetic efficiency and uptake of Ca and K in plants irrespective of salinity stress. The uptake of N and P was higher in AMF plants, and as the salinity increased, the trend showed a decline but had a clear upturn as the salinity stress increased to a high level. The activities of malondialdehyde (MDA), peroxidase (POD), and superoxide dismutase (SOD) as well as the proline content changed due to AMF treatment under salinity stress. The accumulation of proline and catalase (CAT) was observed only when plants experienced moderate salinity stress, but peroxidase (POD) and superoxide dismutase (SOD) were significantly increased in AMF plants irrespective of salinity stress. Taken together, arbuscular mycorrhizal fungi influenced plant growth and physiology, and their effects were more notable when their host plants experienced salinity stress and were influenced by plant and fungal traits.

Influence of fungal endophytes on plant physiology is more pronounced under stress than well-watered conditions: a meta-analysis.

MAIN CONCLUSION: A meta-analysis of published articles shows that the influence of fungal endophytes on plant performance is dependent on plant water status. The magnitude of endophytic effects is higher in plants grown in water-limiting environments than those in adequate watering environments. The outcome of plant-endophyte interactions depends on the identity of the plant host and fungal symbionts. Water limitation often hinders plant productivity in both natural and agricultural settings. Endophytic fungal symbionts can mediate plant water stress responses by enhancing drought tolerance and avoidance, but these effects have not been quantified across plant-endophyte studies. A meta-analysis of published studies was performed to determine how endophytic fungal symbionts influence plant response under non-stressed versus water-stressed conditions. A significantly positive or neutral overall effect of fungal endophyte was noted under water-stressed conditions. In contrast, under non-stressed conditions, the overall effect of fungi on plants was mostly neutral. In general, the presence of fungal endophytes increased plant's total biomass, chlorophyll content, and stomatal conductance irrespective of water availability. In addition, plant shoot biomass, tiller density, plant height, maximum quantum yield (Fv/Fm), net photosynthesis, relative water content (RWC), amounts of ascorbate peroxidase (APX), glutathione (GSH), polyphenol oxidase (PPO), superoxide dismutase (SOD), and phenolics were significantly increased by endophyte colonisation under stressed conditions. Malondialdehyde (MDA) and hydrogen peroxide (H2O2) were reduced in endophytic plants under stress as compared with non-endophytic counterparts. Categorical analysis revealed that accumulation in plant biomass is influenced by factors such as host and fungi identity, the magnitude of which is greater under stressed than non-stressed conditions.

Host Specificity of Endophytic Mycobiota of Wild Nicotiana Plants from Arid Regions of Northern Australia.

In arid regions of northern Australia, plants survive under water deficit, high temperatures, intense solar radiation and nutrient-impoverished soils. They employ various morpho-physiological and biochemical adaptations including interaction with microbial symbionts. We evaluated identity, host and tissue association with geographical distribution of fungal endophytes isolated from above- and below-ground tissues of plants of three indigenous Australian Nicotiana species. Isolation frequency and α-diversity were significantly higher for root endophyte assemblages than those of stem and leaf tissues. We recorded no differences in endophyte species richness or diversity as a function of sampling location, but did detect differences among different host genotypes and plant tissues. There was a significant pattern of community similarity associated with host genotypes but no consistent pattern of fungal community structuring associated with sampling location and tissue type, regardless of the community similarity measurements used.

A simple and rapid in vitro test for large-scale screening of fungal endophytes from drought-adapted Australian wild plants for conferring water deprivation tolerance and growth promotion in Nicotiana benthamiana seedlings.

Some fungal endophytes confer novel phenotypes and enhance existing ones in plants, including tolerance to water deprivation stress. A range of fungal endophytes was isolated from wild Nicotiana plants growing in arid parts of northern Australia. These were screened for ability to enhance water deprivation stress tolerance by inoculating seedlings of the model plant N. benthamiana in two in vitro tests. Sixty-eight endophyte isolates were co-cultivated with N. benthamiana seedlings on either damp filter paper or on agar medium before being subjected to water deprivation. Seventeen isolates were selected for further testing under water deprivation conditions in a sand-based test in a glasshouse. Only two fungal isolates, Cladosporium cladosporioides (E-162) and an unknown fungus (E-284), significantly enhanced seedling tolerance to moisture deprivation consistently in both in vitro and sand-based tests. Although a strongly significant correlation was observed between any two screening methods, the result of filter paper test was more strongly reflected (r = 0.757, p < 0.001) in results of the glasshouse test, indicating its relative suitability over the agar-based test. In another experiment, the same 17 isolates carried forward to the sand-based test used in the glasshouse screening test were inoculated to N. benthamiana plants in pots in a nutrient-limiting environment to test their influence on growth promotion. Isolates related to C. cladosporioides, Fusarium equiseti, and Thozetella sp. promoted seedling growth by increasing shoot length and biomass. The fungal isolate E-162 (C. cladosporioides) significantly enhanced moisture deprivation tolerance as well as promoted seedling growth.