Drought Stress Amelioration in Maize (Zea mays L.) by Inoculation of Bacillus spp. Strains under Sterile Soil Conditions

The aim of the present study was to promote plant growth characteristics including mineral uptake and various phytohormone production by indigenously isolated Bacillus spp. strains. Plants subjected to normal and water stress conditions were collected after 21 days to measure physiological parameters, photosynthetic pigment estimation, biochemical attributes, lipid peroxidation and antioxidant enzyme response modulation. Our results correlated with drought stress amelioration with the inoculation of Bacillus spp. strains BEB1, BEB2, BEB3 and BEB4 under sterile soil condition. Inoculated plants of both maize cultivars showed increases in fresh (56.12%) and dry (103.5%) biomass, plant length (42.48%), photosynthetic pigments (32.76%), and biochemical attributes with enhanced nutrient uptake. The overall maize antioxidant response to bacterial inoculation lowered the malonaldehyde level (59.14%), generation of hydrogen peroxide (45.75%) and accumulation of flavonoid contents in both control and water stress condition. Activity of antioxidant enzymes, catalase (62.96%), peroxidase (23.46%), ascorbate peroxidase (24.44%), and superoxide dismutase (55.69%) were also decreased with the application of bacterial treatment. Stress amelioration is dependent on a specific plant–strain interaction evident in the differences in the evaluated biochemical attributes, lipid peroxidation and antioxidant responses. Such bacteria could be used for enhancing the crop productivity and plant protection under biotic and abiotic stresses for sustainable agriculture.

The effect of plant-fungi interaction generalism on plant community productivity

<p>Plant-plant productivity relationships within ecosystem and community ecology are contentiously debated in the literature due to the numerous factors involved making conclusions hard to draw and disentangle. There are several widely established and supported plant-plant productivity relationships. Increasing species richness can allow for greater niche complementarity, which in turn increases overall above and below ground productivity. Plants with different functional traits can differentially affect a plant community depending on the arrival time of the plant. These priority effects allow certain plants to outcompete others and persist in a community across different temporal scales. Plant species differ in their ability to interact with certain species of symbiotic partners in the soil (Arbuscular mycorrhizal fungi, AMF). This interaction generalism of a plant species indicates the ability of a plant to host many or few AMF species (generalist or specialist, respectively). However, there remains a limited understanding of plant-fungi relationships especially with respect to community productivity and the temporal effects of adding contrasting types of interaction generalism into an established community. The aim of this study was to determine the effects of the addition of an interaction specialist or generalist plant species into an established plant community on the overall community productivity. Three communities that differed in plant species richness were grown for 38 days at which point either a generalist or specialist was added. Community treatments were carried out in field soil, sterile soil and sterile soil reinoculated with viable field soil, separating the effects of plant niche-partitioning for plant-fungi interaction partners from the effects of niche-partitioning for other resources (e.g. soil nutrients). Community productivity was tested using different productivity measures; 1) carbon flux as the Net Ecosystem Exchange (NEE) of the community, 2) total above and below ground plant biomass, 3) neutral lipid fatty acid (NLFA) AMF biomarker, 16:1w5, extracted from total soil and total root mass to assess AMF biomass. It was difficult to disentangle the effects of species richness and interaction generalism on carbon flux in communities, with soil type clearly impacting these relationships. In all soil types, an increase in community plant richness had the greatest effect on carbon draw down and biomass productivity with respect to both plant and AMF biomass. In non-sterilised soil, interaction generalism, specifically the addition of a specialist alongside increased species richness corresponded to increased carbon drawdown. In the context of previous research, this study further highlighted the complexity of factors driving plant-plant-fungi relationships, but clearly identifies the positive role that species richness is having. Although the role of plant-fungi relationships in overall community productive remains unclear, this study provides a platform for future research to be undertaken.</p>

The effect of plant-fungi interaction generalism on plant community productivity

<p>Plant-plant productivity relationships within ecosystem and community ecology are contentiously debated in the literature due to the numerous factors involved making conclusions hard to draw and disentangle. There are several widely established and supported plant-plant productivity relationships. Increasing species richness can allow for greater niche complementarity, which in turn increases overall above and below ground productivity. Plants with different functional traits can differentially affect a plant community depending on the arrival time of the plant. These priority effects allow certain plants to outcompete others and persist in a community across different temporal scales. Plant species differ in their ability to interact with certain species of symbiotic partners in the soil (Arbuscular mycorrhizal fungi, AMF). This interaction generalism of a plant species indicates the ability of a plant to host many or few AMF species (generalist or specialist, respectively). However, there remains a limited understanding of plant-fungi relationships especially with respect to community productivity and the temporal effects of adding contrasting types of interaction generalism into an established community. The aim of this study was to determine the effects of the addition of an interaction specialist or generalist plant species into an established plant community on the overall community productivity. Three communities that differed in plant species richness were grown for 38 days at which point either a generalist or specialist was added. Community treatments were carried out in field soil, sterile soil and sterile soil reinoculated with viable field soil, separating the effects of plant niche-partitioning for plant-fungi interaction partners from the effects of niche-partitioning for other resources (e.g. soil nutrients). Community productivity was tested using different productivity measures; 1) carbon flux as the Net Ecosystem Exchange (NEE) of the community, 2) total above and below ground plant biomass, 3) neutral lipid fatty acid (NLFA) AMF biomarker, 16:1w5, extracted from total soil and total root mass to assess AMF biomass. It was difficult to disentangle the effects of species richness and interaction generalism on carbon flux in communities, with soil type clearly impacting these relationships. In all soil types, an increase in community plant richness had the greatest effect on carbon draw down and biomass productivity with respect to both plant and AMF biomass. In non-sterilised soil, interaction generalism, specifically the addition of a specialist alongside increased species richness corresponded to increased carbon drawdown. In the context of previous research, this study further highlighted the complexity of factors driving plant-plant-fungi relationships, but clearly identifies the positive role that species richness is having. Although the role of plant-fungi relationships in overall community productive remains unclear, this study provides a platform for future research to be undertaken.</p>

Latent Pathogenic Fungi in the Medicinal Plant Houttuynia cordata Thunb. Are Modulated by Secondary Metabolites and Colonizing Microbiota Originating from Soil

Latent pathogenic fungi (LPFs) affect plant growth, but some of them may stably colonize plants. LPFs were isolated from healthy Houttuynia cordata rhizomes to reveal this mechanism and identified as Ilyonectria liriodendri, an unidentified fungal sp., and Penicillium citrinum. Sterile H. cordata seedlings were cultivated in sterile or non-sterile soils and inoculated with the LPFs, followed by the plants’ analysis. The in vitro antifungal activity of H. cordata rhizome crude extracts on LPF were determined. The effect of inoculation of sterile seedlings by LPFs on the concentrations of rhizome phenolics was evaluated. The rates of in vitro growth inhibition amongst LPFs were determined. The LPFs had a strong negative effect on H. cordata in sterile soil; microbiota in non-sterile soil eliminated such influence. There was an interactive inhibition among LPFs; the secondary metabolites also regulated their colonization in H. cordata rhizomes. LPFs changed the accumulation of phenolics in H. cordata. The results provide that colonization of LPFs in rhizomes was regulated by the colonizing microbiota of H. cordata, the secondary metabolites in the H. cordata rhizomes, and the mutual inhibition and competition between the different latent pathogens.

Production, stability and degradation of Trichoderma gliotoxin in growth medium, irrigation water and agricultural soil

Gliotoxin produced by Trichoderma virens is inhibitory against various phytopathogenic fungi and bacteria. However, its stability in soil-ecosystem has not yet been well-defined. This study aimed to decipher its persistence and behaviour in growth media, irrigation water and soil ecosystems. Gliotoxin production was noticed at logarithmic growth phase and converted into bis-thiomethyl gliotoxin at late stationary growth phase of T. virens in acidic growth medium. But, no gliotoxin production was observed in neutral and alkaline growth medium. Gliotoxin was stable for several days in acidic water but degraded in alkaline water. Degradation of gliotoxin was more in unsterile soil than sterile soil and also that was higher under wet soil than dry soil. Degradation of gliotoxin was hastened by alkaline pH in wet soil but not in dry soil. Under unsterile soil conditions, high soil moisture increased the degradation of gliotoxin and the degradation of gliotoxin occurred quickly in alkaline soil (in 5 days) compared to acidic soil (in 10 days). Under sterile soil conditions, high soil moisture also enhanced the degradation of gliotoxin but level of degradation was less compared to unsterile conditions. Thus, gliotoxin stability is influenced mainly by the soil wetness, soil microbial community and pH conditions.

Role of Rhizospheric Microbiota as a Bioremediation Tool for the Protection of Soil-Plant Systems from Microcystins Phytotoxicity and Mitigating Toxin-Related Health Risk

Frequent toxic cyanoblooms in eutrophic freshwaters produce various cyanotoxins such as the monocyclic heptapeptides microcystins (MCs), known as deleterious compounds to plant growth and human health. Recently, MCs are a recurrent worldwide sanitary problem in irrigation waters and farmland soils due to their transfer and accumulation in the edible tissues of vegetable produce. In such cases, studies about the persistence and removal of MCs in soil are scarce and not fully investigated. In this study, we carried out a greenhouse trial on two crop species: faba bean (Vicia faba var. Alfia 321) and common wheat (Triticum aestivum var. Achtar) that were grown in sterile (microorganism-free soil) and non-sterile (microorganism-rich soil) soils and subjected to MC-induced stress at 100 µg equivalent MC-LR L−1. The experimentation aimed to assess the prominent role of native rhizospheric microbiota in mitigating the phytotoxic impact of MCs on plant growth and reducing their accumulation in both soils and plant tissues. Moreover, we attempted to evaluate the health risk related to the consumption of MC-polluted plants for humans and cattle by determining the estimated daily intake (EDI) and health risk quotient (RQ) of MCs in these plants. Biodegradation was liable to be the main removal pathway of the toxin in the soil; and therefore, bulk soil (unplanted soil), as well as rhizospheric soil (planted soil), were used in this experiment to evaluate the accumulation of MCs in the presence and absence of microorganisms (sterile and non-sterile soils). The data obtained in this study showed that MCs had no significant effects on growth indicators of faba bean and common wheat plants in non-sterile soil as compared to the control group. In contrast, plants grown in sterile soil showed a significant decrease in growth parameters as compared to the control. These results suggest that MCs were highly bioavailable to the plants, resulting in severe growth impairments in the absence of native rhizospheric microbiota. Likewise, MCs were more accumulated in sterile soil and more bioconcentrated in root and shoot tissues of plants grown within when compared to non-sterile soil. Thereby, the EDI of MCs in plants grown in sterile soil was more beyond the tolerable daily intake recommended for both humans and cattle. The risk level was more pronounced in plants from the sterile soil than those from the non-sterile one. These findings suggest that microbial activity, eventually MC-biodegradation, is a crucial bioremediation tool to remove and prevent MCs from entering the agricultural food chain.

Impact of Encapsulation on Plantlet Regeneration from in vitro Grown Shoot tips of Citrus aurantifolia (Lime)

In order to conserve diverse species of citrus, an experiment on in vitro micropropagation and production of synthetic seeds from in vitro regenerated plant propagules of the species; Citrus aurantifolia (Lime) was carried out in which shoot tips were found to be suitable for excapsulation of artificial seeds. Highest rate of germination was obtained from the shoot tips when MS was supplemented with 1 mg/l BAP. Beaded shoot tips produced maximum germination (81.43%). Germinated synthetic seeds with well established roots and shoots were were taken out from the culture bottles and transferred in plastic cups containing a mixture of sterile soil: sand and farmyard manure at a ratio of 1:1:1. Seedlings were further shifted in earthen pots and kept in a partial shed net house for 7 days. Those seedlings were finally transferred under the field conditions for acclimatization. Plant Tissue Cult. & Biotech. 31(1): 43-49, 2021 (June)

Biological control of Western flower thrips, Frankliniella occidentalis using a self-sustaining granular fungal treatment

Western flower thrips (WFT), Frankliniella occidentalis, is one of the most destructive pests of vegetables, fruits and ornamental crops worldwide, causing extensive damage by direct feeding of the crop and transmitting economically important viruses. Despite the successes of biocontrol agents to control WFT, more efficient and cost-effective ways must be found to encourage grower adoption of integrated pest management. A sustainable fungal treatment was developed to preserve fungal inoculum in potting soil and reduce thrips populations. Combining cooked, oven-dried millet with BotaniGard® (a commercial form of Beauveria bassiana strain GHA) to potting soil increased spore production and persistence of the fungus in the soil. In treated pots with millet, spore concentrations were 3–4 times greater after 30 days compared with spore yields at 10 days. The number of WFT adults was significantly lower in the marigold pots treated with GHA mix + millet than untreated controls, 12% and 10% in treated pots and 70% and 68% in untreated pots in sterile and non-sterile soil, respectively. Incorporation of millet in the potting mix enhanced the effect of the fungal treatments by providing a nutritive substrate on which the fungus could become established. This method is relatively inexpensive and easy for growers to use in greenhouses because granular formulations of B. bassiana are not commercially available.

Soil Reservoir Dynamics of Ophidiomyces ophidiicola, the Causative Agent of Snake Fungal Disease

Wildlife diseases pose an ever-growing threat to global biodiversity. Understanding how wildlife pathogens are distributed in the environment and the ability of pathogens to form environmental reservoirs is critical to understanding and predicting disease dynamics within host populations. Snake fungal disease (SFD) is an emerging conservation threat to North American snake populations. The causative agent, Ophidiomyces ophidiicola (Oo), is detectable in environmentally derived soils. However, little is known about the distribution of Oo in the environment and the persistence and growth of Oo in soils. Here, we use quantitative PCR to detect Oo in soil samples collected from five snake dens. We compare the detection rates between soils collected from within underground snake hibernacula and associated, adjacent topsoil samples. Additionally, we used microcosm growth assays to assess the growth of Oo in soils and investigate whether the detection and growth of Oo are related to abiotic parameters and microbial communities of soil samples. We found that Oo is significantly more likely to be detected in hibernaculum soils compared to topsoils. We also found that Oo was capable of growth in sterile soil, but no growth occurred in soils with an active microbial community. A number of fungal genera were more abundant in soils that did not permit growth of Oo, versus those that did. Our results suggest that soils may display a high degree of both general and specific suppression of Oo in the environment. Harnessing environmental suppression presents opportunities to mitigate the impacts of SFD in wild snake populations.

Rhizosphere Streptomyces formulas as the biological control agent of phytopathogenic fungi Fusarium oxysporum and plant growth promoter of soybean

Sari M, Nawangsih AA, Wahyudi AT. 2021. Rhizosphere Streptomyces formulas as the biological control agent of phytopathogenic fungi Fusarium oxysporum and plant growth promoter of soybean. Biodiversitas 22: 3015-3023. Rhizosphere Streptomyces are considered as promising sources of plant growth-promoting rhizobacteria (PGPR) and biocontrol agents against pathogenic fungi, particularly Fusarium oxysporum causing root rot, cotyledon rot, hypocotyl rot, and stunted growth in soybean. Formulation of rhizosphere Streptomyces with appropriate carrier materials is necessary to facilitate storage and application in plants. This study aimed to develop a formulation of rhizosphere Streptomyces, apply the formula to control F. oxysporum, and promote soybean plant growth. Five Streptomyces isolates, i.e., Streptomyces panaciradicis ARK 13, Streptomyces tritolerans ARK 17, Streptomyces recifensis ARK 63, Streptomyces tendae ARK 91, and Streptomyces manipurensis ARK 94 were used in this study. All of the isolates could grow in potato broth, rice bran extract, and molasses as alternative media. The highest biomass produced from the molasses growth medium. All five isolates had antifungal activity against F. oxysporum with the inhibition percentage ranging from 41% to 76%, and all of them were detected to have the iaaM gene. Indole-3-acetic acid (IAA) hormone produced by these isolates were ranging from 8.99-15.14 mg L-1, with the phosphate solubilization index of 2.13-2.47. Five rhizosphere Streptomyces formulas with the main carrier of peat could maintain the viability with the population density of 108 CFU g-1 for 8 weeks of storage at room temperature. Two formulas, F17 and F94, were the best formulas to control disease caused by F. oxysporum with disease suppression of 74% in sterile soil and 80-85% in non-sterile soil. Formula F17 and F94 significantly increased soybean growth in sterile and non-sterile soils. Therefore, these formulas could be recommended as biocontrol and plant growth promoters of soybean.