Photosynthetic bacterium Rhodopseudomonas palustris GJ‐22 induces systemic resistance against viruses

Photosynthetic bacteria (PSB) have been extensively used in agriculture to promote plant growth and to improve crop quality. Their potential application in plant disease management, however, is largely overlooked. In this study, the PSB strain Rhodopseudomonas palustris GJ‐22 was investigated for its ability to induce resistance against a plant virus while promoting plant growth. In the field, a foliar spray of GJ‐22 suspension protected tobacco plants against tobacco mosaic virus (TMV). Under axenic conditions, GJ‐22 colonized the plant phyllosphere and induced resistance against TMV. Additionally, GJ‐22 produced two phytohormones, indole‐3‐acetic acid and 5‐aminolevulinic acid, which promote growth and germination in tobacco. Furthermore, GJ‐22‐inoculated plants elevated their immune response under subsequent TMV infection. This research may give rise to a novel biological agent with a dual function in disease management while promoting plant growth.     

Improved germination efficiency of Salicornia ramosissima seeds inoculated with Bacillus aryabhattai SP1016‐20

Saline agriculture and the crop cultivation of halophytes represent an alternative for the reclamation of salinized soils and for the management of irrigation water. Halotolerant plant growth promoting bacteria with biocontrol effect, as an alternative to commercial fungicides, may contribute to improve crop productivity while mitigating saline stress effects. The objective of this work was to isolate autochthonous rhizobacteria with biocontrol features, to be used as germination enhancers and plant‐growth promoting agents in the crop cultivation of Salicornia ramosissima. A set of isolates obtained from the rhizosphere of S. ramosissima was characterised in terms of Gram, motility, salt tolerance and biocontrol traits (hydrogen cyanide production, antifungal activity and production of extracellular lipases and proteases). One Gram‐positive motile isolate that tested positive for all biocontrol traits was identified by 16S rRNA gene sequencing as Bacillus aryabhattai. The inoculation of S. ramosissima seeds with B. aryabhattai SP1016‐20 reduced the negative effect of salinity on the germination efficiency. At the highest tested salinity (30 g/L NaCl) the final germination efficiency of inoculated seeds doubled in relation to non‐inoculated controls. Although the mechanisms involved in the biocontrol effect were not defined in the current work, the results highlight the potential of Bacillus aryabhattai SP1016‐20 as a plant‐growth promoting agent for the crop cultivation of Salicornia and contribute to the strengthening of the scientific basis of biosaline agriculture and plant growth promoting rhizobacteria‐assisted crop cultivation of halophytes in saline soils and estuarine sediments.     

Plant‐derived recombinant human serum transferrin demonstrates multiple functions

Human serum transferrin (hTf) is the major iron‐binding protein in human plasma, having a vital role in iron transport. Additionally, hTf has many other uses including antimicrobial functions and growth factor effects on mammalian cell proliferation and differentiation. The multitask nature of hTf makes it highly valuable for different therapeutic and commercial applications. However, the success of hTf in these applications is critically dependent on the availability of high‐quality hTf in large amounts. In this study, we have developed plants as a novel platform for the production of recombinant (r)hTf. We show here that transgenic plants are an efficient system for rhTf production, with a maximum accumulation of 0.25% total soluble protein (TSP) (or up to 33.5 μg/g fresh leaf weight). Furthermore, plant‐derived rhTf retains many of the biological activities synonymous with native hTf. In particular, rhTf reversibly binds iron in vitro, exhibits bacteriostatic activity, supports cell proliferation in serum‐free medium and can be internalized into mammalian cells in vitro. The success of this study validates the future application of plant rhTf in a variety of fields. Of particular interest is the use of plant rhTf as a novel carrier for cell‐specific or oral delivery of protein/peptide drugs for the treatment of human diseases such as diabetes. To demonstrate this hypothesis, we have additionally expressed an hTf fusion protein containing glucagon‐like peptide 1 (GLP‐1) or its derivative in plants. Here, we show that plant‐derived hTf‐GLP‐1 fusion proteins retain the ability to be internalized by mammalian cells when added to culture medium in vitro.     

Potential for plant growth promotion by a consortium of stress‐tolerant 2,4‐dinitrotoluene‐degrading bacteria: isolation and characterization of a military soil

The presence of explosives in soils and the interaction with drought stress and nutrient limitation are among the environmental factors that severely affect plant growth on military soils. In this study, we seek to isolate and identify the cultivable bacteria of a 2,4‐dinitrotoluene (DNT) contaminated soil (DS) and an adjacent grassland soil (GS) of a military training area aiming to isolate new plant growth‐promoting (PGP) and 2,4‐DNT‐degrading strains. Metabolic profiling revealed disturbances in Ecocarbon use in the bare DS; isolation of cultivable strains revealed a lower colony‐forming‐unit count and a less diverse community associated with DS in comparison with GS. New 2,4‐DNT‐tolerant strains were identified by selective enrichments, which were further characterized by auxanography for 2,4‐DNT use, resistance to drought stress, cold, nutrient starvation and PGP features. By selecting multiple beneficial PGP and abiotic stress‐resistant strains, efficient 2,4‐DNT‐degrading consortia were composed. After inoculation, consortium UHasselt Sofie 3 with seven members belonging to Burkholderia, Variovorax, Bacillus, Pseudomonas and Ralstonia species was capable to successfully enhance root length of Arabidopsis under 2,4‐DNT stress. After 9 days, doubling of main root length was observed. Our results indicate that beneficial bacteria inhabiting a disturbed environment have the potential to improve plant growth and alleviate 2,4‐DNT stress.     

Agro-industrial waste materials and wastewater sludge for rhizobial inoculant production: a review

Inoculating legumes with commercial rhizobial inoculants is a common agriculture practice. Generally, inoculants are sold in liquid or in solid forms (mixed with carrier). The production of inoculants involves a step in which a high number of cells are produced, followed by the product formulation. This process is largely governed by the cost related to the medium used for rhizobial growth and by the availability of a carrier source (peat) for production of solid inoculant. Some industrial and agricultural by-products (e.g. cheese whey, malt sprouts) contain growth factors such as nitrogen and carbon, which can support growth of rhizobia. Other agro-industrial wastes (e.g. plant compost, filtermud, fly-ash) can be used as a carrier for rhizobial inoculant. More recently, wastewater sludge, a worldwide recyclable waste, has shown good potential for inoculant production as a growth medium and as a carrier (dehydrated sludge). Sludge usually contains nutrient elements at concentrations sufficient to sustain rhizobial growth and heavy metals are usually below the recommended level. In some cases, growth conditions can be optimized by a sludge pre-treatment or by the addition of nutrients. Inoculants produced in wastewater sludge are efficient for nodulation and nitrogen fixation with legumes as compared to standard inoculants. This new approach described in this review offers a safe environmental alternative for both waste treatment/disposal and inoculant production.     

Evidence for species‐specific plant responses to soil microbial communities from remnant and degraded land provides promise for restoration

Below‐ground interactions between soil microbial communities and plants play important roles in shaping plant community structure, but are currently poorly understood. Understanding these processes has important practical implications, including for restoration. In this study, we investigated whether soil microbes from remnant areas can aid the restoration of old‐fields, and whether soil microbes from an old‐field encourages further invasive establishment. In a glasshouse experiment, we measured growth and survival of two native grasses (Austrostipa nodosa and Rytidosperma auriculatum) and an invasive grass (Lolium rigidum) grown in sterile soil inoculated with whole soil from three locations: an old‐field, a remnant grassland, and a seed orchard planted with native grasses 7 years ago. Plants grown in sterile, non‐inoculated soil acted as controls. The orchard inoculant was included to test whether soil microbes from an area cultivated with native grasses induced plant responses similar to remnant areas. The remnant treatment resulted in the highest biomass and no mortality for R. auriculatum. All inoculant types increased the biomass of the invasive species equally. The native grass, A. nodosa, was the most sensitive to the addition of inoculum, whereas the invasive L. rigidum suffered very low mortality across all treatments. Overall, mortality was highest in the old‐field treatment at 42.9%. These results give insights into how soil microbes can affect community structure and dynamics, e.g. the high mortality of natives with old‐field inoculant may be one mechanism that allows invasive species to dominate. Poorer performance of native species with the orchard inoculant suggests it would not make a suitable replacement for remnant soil; therefore, more work is needed to understand the requirements of target species and their interactions before this technique can be exploited to maximum benefit.     

Bio‐priming seeds with cyanobacteria: effects on native plant growth and soil properties

Cyanobacteria are photosynthetic bacteria that form a fundamental part of soil biocrusts, enhance soil function and structure, and can promote plant growth. We assessed the potential of cyanobacteria as a seed bio‐primer for mine‐site restoration in an arid region in Western Australia, examining its effects on native plant growth and the characteristics of mine soil substrates used in dryland restoration. Cyanobacteria strains indigenous to the study region (Leptolyngbya sp., Microcoleus sp., Nostoc sp., and Scytonema sp.) were used to create an inoculant. Seeds of seven native plant species were bio‐primed with the inoculant, and their germination and growth assessed in a laboratory experiment. Seedling growth after bio‐priming was assessed in a glasshouse experiment for a subset of three species, in two different substrates (topsoil and mine waste). Soil properties related to soil function, e.g. total organic carbon, total nitrogen, and microbial activity, were also measured. Minor effects on germination were recorded with only significantly higher germination rates reported in E. gamophylla. Soil parameters were generally higher in topsoil than in mine waste, regardless of bio‐priming treatment. However, bio‐priming resulted in seedlings of four species producing longer radicles and/or shoots. For example, seedling root lengths of bio‐primed G. wickhamii were 57% larger than the control treatment (30.1 ± 4.3 and 13.0 ± 1.6 mm, respectively); and shoots of T. wiseana were 54% longer in the bio‐primed treatment (18.6 ± 1.6 mm) compared to the control (8.53 ± 1.4 mm). Overall, our results highlight that bio‐priming with cyanobacteria may improve plant growth for some species commonly used in dryland restoration.     

Bradyrhizobium strains and the nodulation,nodule efficiency and growth of soybean (Glycine max L.) in Egyptian soils

Six strains and a commercial inoculant ofBradyrhizobium japonicum were evaluated in association withGlycine max (L.) cultivar Clark. Inoculated and uninoculated plants were grown in pot and field experiments. Nodules were counted and weighed and roots and shoots were separated and analysed for total nitrogen. In pot experiments, two of six bacterial strains were superior to the other four, and to the commercial inoculant (Nitragin) in promoting greater root and top growth and plant nitrogen accumulation. In the field experiment, there were indications that environmental conditions may have affected nodulation by the bacteria. The strains could be divided into three groups according to nodule efficiencies, accumulation of plant dry matter, and total nitrogen content. The greater variations in nodule efficiencies of the tested strains could be attributed to the quantities of bacteroid, cytosol protein and leghaemoglobin in the nodules.     

Metabolomic profiling of wild‐type and mutant soybean root nodules using laser‐ablation electrospray ionization mass spectrometry reveals altered metabolism

The establishment of the nitrogen‐fixing symbiosis between soybean and Bradyrhizobium japonicum is a complex process. To document the changes in plant metabolism as a result of symbiosis, we utilized laser ablation electrospray ionization‐mass spectrometry (LAESI‐MS) for in situ metabolic profiling of wild‐type nodules, nodules infected with a B. japonicum nifH mutant unable to fix nitrogen, nodules doubly infected by both strains, and nodules formed on plants mutated in the stearoyl‐acyl carrier protein desaturase (sacpd‐c) gene, which were previously shown to have an altered nodule ultrastructure. The results showed that the relative abundance of fatty acids, purines, and lipids was significantly changed in response to the symbiosis. The nifH mutant nodules had elevated levels of jasmonic acid, correlating with signs of nitrogen deprivation. Nodules resulting from the mixed inoculant displayed similar, overlapping metabolic distributions within the sectors of effective (fix⁺) and ineffective (nifH mutant, fix^?) endosymbionts. These data are inconsistent with the notion that plant sanctioning is cell autonomous. Nodules lacking sacpd‐c displayed an elevation of soyasaponins and organic acids in the central necrotic regions. The present study demonstrates the utility of LAESI‐MS for high‐throughput screening of plant phenotypes. Overall, nodules disrupted in the symbiosis were elevated in metabolites related to plant defense.     

Influence of inoculation with a Trichoderma bio‐inoculant on ectomycorrhizal colonisation of Pinus radiata seedlings

Trichoderma species, through mechanisms such as mycoparasitism, antibiosis, induced resistance and competition, are able to suppress the growth and activity of soil microbes and therefore have the potential to influence ectomycorrhizal (ECM) fungal colonisation. ECM colonisation potential of Pinus radiata seedlings inoculated with the commercially available Trichoderma species bio‐inoculant, ArborGuard?, was investigated in a commercial containerised nursery setting and in a separate glasshouse experiment. Application of ArborGuard? to P. radiata seedlings in both the containerised nursery and glasshouse experiment had no detrimental effect on the ability of the naturally occurring ECM fungi to colonise the seedlings. Thelephora terrestris was the only ECM species colonising the P. radiata root tips in the containerised system while Tomentella ellisii was the dominant species found colonising the P. radiata root tips in the glasshouse experiment. No seedling growth promotion was observed with the addition of ArborGuard?. The results show that the Trichoderma bio‐inoculant ArborGuard? does not affect ECM colonisation of P. radiata seedlings by Th. terrestris and T. ellisii in a containerised nursery system.     

Safety assessment of biocontrol and plant growth‐promoting pseudomonads useful in crop production

One biocontrol and two plant growth‐promoting Pseudomonas spp. isolates were subjected to a safety assessment. Potential risks for human and plant health were investigated and screenings for toxic effects were performed. The antibiotic susceptibility pattern was typical for Pseudomonas and only one of the isolates grew at 37°C. None of the isolates elicited a hypersensitivity reaction in the tobacco test for plant pathogenicity. For toxicity testing, BACTOX, the Lemna growth bioassay, primary root and shoot growth in vitro and a seed germination/early seedling growth assay were performed. In these assays, one of the plant growth‐promoting isolates consistently displayed concentration‐dependent adverse effects not seen with the other isolates. Further investigation is needed to determine whether these adverse effects are a concern from a safety assessment perspective, as the identity and mode of action of the active metabolite(s) are unknown. Lack of standardised test procedures for complex samples of microbial origin hampered interpretation of the results from the toxicity assays and there is a need to develop methodology that is more suitable for testing such samples. Nevertheless, the tests employed for the three Pseudomonas isolates were successful in distinguishing isolates with different characteristics. This test framework provides an outline for information collection and safety evaluation when handling new microbial isolates that could be an efficient tool in selecting the best candidate isolates for product development.     

Carbohydrate as Fuel for Foraging,Resource Defense and Colony Growth – a Long‐term Experiment with the Plant‐ant Crematogaster nigriceps

Mismatches in nutrient composition (e.g., protein, carbohydrates, lipids, etc.) between consumers and the resources they depend on can have ecological consequences, affecting traits from individual behavior to community structure. In many terrestrial ecosystems, ants depend on plant and insect mutualist partners for carbohydrate‐rich rewards that are nutritionally unbalanced (especially in protein) relative to colony needs. Despite imbalances, many carbohydrate‐feeding ant mutualists dominate communities—both competitively and numerically—raising the question of whether excess carbohydrates ‘fuel’ colony acquisition of limiting resources and growth. In a 10‐month field study, we manipulated carbohydrate access for the obligate plant‐ant Crematogaster nigriceps to test whether carbohydrate availability could be mechanistically linked to ecological dominance via heightened territory defense, increased protein foraging, and colony growth. Supplementation increased aggressive defense of hosts after only two weeks, but was also strongly linked to variation in rainfall. Contrary to predictions, we did not find that supplemented colonies increased protein foraging. Instead, colonies with reduced carbohydrate access discovered a greater proportion of protein baits, suggesting that carbohydrate deprivation increases foraging intensity. We found no significant effect of carbohydrate manipulation on brood or alate production. These results contrast with findings from several recent short‐term and lab‐based nutrient supplementation studies and highlight the role of seasonality and biotic context in colony‐foraging and reproductive decisions. These factors may be essential to understanding the consequences of carbohydrate access in natural plant‐ant systems.     

Plant growth‐promoting endophytic bacteria augment growth and salinity tolerance in rice plants

• Salt stress negatively affects growth and development of plants. However, it is hypothesized that plant growth‐promoting endophytic bacteria can greatly alleviate the adverse effects of salinity and can promote growth and development of plants. In the present research, we aimed to isolate endophytic bacteria from halotolerant plants and evaluate their capacity for promoting crop plant growth.
• The bacterial endophytes were isolated from selected plants inhabiting sand dunes at Pohang beach, screened for plant growth‐promoting traits and applied to rice seedlings under salt stress (NaCl; 150 mm ).
• Out of 59 endophytic bacterial isolates, only six isolates, i.e. Curtobacterium oceanosedimentum SAK1, Curtobacterium luteum SAK2, Enterobacter ludwigii SAK5, Bacillus cereus SA1, Micrococcus yunnanensis SA2, Enterobacter tabaci SA3, resulted in a significant increase in the growth of Waito‐C rice. The cultural filtrates of bacterial endophytes were tested for phytohormones, including indole‐3‐acetic acid, gibberellins and organic acids. Inoculation of the selected strains considerably reduced the amount of endogenous ABA in rice plants under NaCl stress, however, they increased GSH and sugar content. Similarly, these strains augmented the expression of flavin monooxygenase (OsYUCCA1) and auxin efflux carrier (OsPIN1) genes under salt stress.
• In conclusion, the pragmatic application of the above selected bacterial strains alleviated the adverse effects of NaCl stress and enhanced rice growth attributes by producing various phytohormones.

     

Proteome reference map for the plant growth‐promoting bacterium Pseudomonas putida UW4

A proteome reference map containing 326 2‐D gel spots representing 275 different proteins was constructed for the plant growth‐promoting bacterium Pseudomonas putida UW4. Protein identifications were obtained using Q‐TOF MS/MS spectra matching to homologous proteins from other Pseudomonas strains and confirmed by PMF analysis. This data set is accessible at http://world‐2dpage.expasy.org/repository/ and will aid in further characterization of Pseudomonas strains and interactions of plant growth‐promoting bacterium with the plant rhizosphere environment.     

Stimulation of the growth of <Emphasis Type="Italic">Jatropha curcas</Emphasis> by the plant growth promoting bacterium <Emphasis Type="Italic">Enterobacter cancerogenus</Emphasis> MSA2

A novel Enterobacter cancerogenus MSA2 is a plant growth promoting gamma-proteobacterium that was isolated from the rhizosphere of Jatropha cucas a potentially important biofuel feed stock plant. Based on phenotypic, physiological, biochemical and phylogenetic studies, strain MSA2 could be classified as a member of E. cancerogenus. However, comparisons of characteristics with other known species of the genus Enterobacter suggested that strain MSA2 could be a novel PGPB strain. In vitro studies were carried for the plant growth promoting attribute of this culture. It tested positive for ACC (1-aminocyclopropane-1-carboxylic acid) deaminase production, phytase, phosphate solubilization, IAA (Indole acetic acid) production, siderophore, and ammonia production. The isolate was then used as a inoculant for the vegetative study of Jatropha curcas plant. Enterobacter cancerogenus MSA2 supplemented with 1% carboxymethylcellulose showed overall plant growth promotion effect resulting in enhanced root length (124.14%), fresh root mass (81%), fresh shoot mass (120.02%), dry root mass (124%), dry shoot mass (105.54%), number of leaf (30.72%), chlorophyll content (50.41%), and biomass (87.20%) over control under the days of experimental observation. This study was designed for 120 days and was in triplicate and the data was collected at every 30 days.     

Advanced photobioreactor LED illumination system: Scale‐down approach to study microalgal growth kinetics

A newly designed and constructed LED illumination device for commercial cylindrical bioreactors is presented for application in microalgal cultivations and investigation of growth kinetics. An ideally illuminated volume is achieved by focusing the light toward the center of the reactor and thereby compensating the mutual shading of the cells. The relevant biomass concentration for homogeneous illumination depending on reactor radius was determined by light distribution measurements for Chlamydomonas to 0.2 g/L (equal 0.435 optical density at 750 nm). It is shown that cultivation experiments with the newly designed illumination device operated in batch mode can be successfully applied for determination of growth rates and photo conversion efficiencies. The exact knowledge of physiological reactions of specific strain(s) and the estimation of relevant parameters for scale‐up can be used for construction of economic pilot plant photobioreactors. The determination of light‐dependent kinetics of growth and product formation is the first necessary step to achieve this. A wide variety of different parameters can be examined like the effect of different illumination conditions (light intensity, frequency of day/night cycles, flashing light, light color…) and thereby for each single application specific, relevant, and interesting parameters will be examined.     

Trait‐abundance relation in response to nutrient addition in a Tibetan alpine meadow: The importance of species trade‐off in resource conservation and acquisition

In competition‐dominated communities, traits promoting resource conservation and competitive ability are expected to have an important influence on species relative abundance (SRA). Yet, few studies have tested the trait‐abundance relations in the line of species trade‐off in resource conservation versus acquisition, indicating by multiple traits coordination. We measured SRA and key functional traits involving leaf economic spectrum (SLA, specific leaf area; LDMC, leaf dry matter content; LCC, leaf carbon concentration; LNC, leaf nitrogen concentration; LPC, leaf phosphorus concentration; Hs, mature height) for ten common species in all plots subjected to addition of nitrogen fertilizer (N), phosphorus fertilizer (P), or both of them (NP) in a Tibetan alpine meadow. We test whether SRA is positively related with traits promoting plant resource conservation, while negatively correlated with traits promoting plant growth and resource acquisition. We found that species were primarily differentiated along a trade‐off axis involving traits promoting nutrient acquisition and fast growth (e.g., LPC and SLA) versus traits promoting resource conservation and competition ability (e.g., large LDMC). We further found that SRA was positively correlated with plant height, LDMC, and LCC, but negatively associated with SLA and leaf nutrient concentration irrespective of fertilization. A stronger positive height‐SRA was found in NP‐fertilized plots than in other plots, while negative correlations between SRA and SLA and LPC were found in N or P fertilized plots. The results indicate that species trade‐off in nutrient acquisition and resource conservation was a key driver of SRA in competition‐dominated communities following fertilization, with the linkage between SRA and traits depending on plant competition for specific soil nutrient and/or light availability. The results highlight the importance of competitive exclusion in plant community assembly following fertilization and suggest that abundant species in local communities become dominated at expense of growth while infrequent species hold an advantage in fast growth and dispersals to neighbor meta‐communities.     

The role of a class III gibberellin 2‐oxidase in tomato internode elongation

A network of environmental inputs and internal signaling controls plant growth, development and organ elongation. In particular, the growth‐promoting hormone gibberellin (GA) has been shown to play a significant role in organ elongation. The use of tomato as a model organism to study elongation presents an opportunity to study the genetic control of internode‐specific elongation in a eudicot species with a sympodial growth habit and substantial internodes that can and do respond to external stimuli. To investigate internode elongation, a mutant with an elongated hypocotyl and internodes but wild‐type petioles was identified through a forward genetic screen. In addition to stem‐specific elongation, this mutant, named tomato internode elongated ‐1 (tie‐1) is more sensitive to the GA biosynthetic inhibitor paclobutrazol and has altered levels of intermediate and bioactive GAs compared with wild‐type plants. The mutation responsible for the internode elongation phenotype was mapped to GA2oxidase 7, a class III GA 2‐oxidase in the GA biosynthetic pathway, through a bulked segregant analysis and bioinformatic pipeline, and confirmed by transgenic complementation. Furthermore, bacterially expressed recombinant TIE protein was shown to have bona fide GA 2‐oxidase activity. These results define a critical role for this gene in internode elongation and are significant because they further the understanding of the role of GA biosynthetic genes in organ‐specific elongation.     

Rhizobacteria improve sugarcane growth and photosynthesis under well‐watered conditions

Morpho‐physiological changes caused by particular plant growth‐promoting rhizobacteria were evaluated in sugarcane plants under varying water availability. Under well‐watered conditions, we have found one rhizobacteria isolate (IAC‐RBcr5) able to enhance root dry matter and photosynthesis of sugarcane plants. The IAC‐RBcr5 genome was sequenced and high similarity was found with Pseudomonas putida GB‐1. Based on increased root system size of inoculated plants, we hypothesised that sugarcane plants inoculated with IAC‐RBcr5 would have improved performance under water deficit. Although IAC‐RBcr5 had improved plant leaf CO₂ assimilation under water shortage, inoculation caused reduction of biomass accumulation in sugarcane. The negative influence of water deficit on shoot growth rate and root traits such as volume, area, diameter, length and specific root area was higher in plants treated with IAC‐RBcr5 as compared to non‐inoculated ones. However, rhizobacteria‐induced improvements in leaf and root proline contents would represent a strategy for storing carbon and nitrogen during low water availability and helping both organisms to resume their metabolism after rehydration. In conclusion, we found and identified a rhizobacterium able to improve growth and photosynthesis of sugarcane plants. Such benefit for plant growth was lost under low water availability as a likely consequence of increased carbon‐energy demand by rhizobacteria and their sensitivity to drought.     

Secondary metabolites produced by a root‐inhabiting sterile fungus antagonistic towards pathogenic fungi

Aims: A sterile red fungus (SRF) isolated from cortices of roots of both wheat (Triticum aestivum cv. Gamenya) and ryegrass (Lolium rigidum cv. Wimmera) was found to protect the hosts from phytopathogens and promote plant growth. In this work, the major secondary metabolites produced by this SRF were analysed, and their antibiotic and plant‐growth‐promoting activities investigated. Methods and Results: Two main compounds, veratryl alcohol (VA) and 4‐(hydroxymethyl)‐quinoline, were isolated from the culture filtrate of the fungus. In antifungal assays, VA inhibited the growth of Sclerotinia sclerotiorum and Pythium irregulare even at low amounts, while high concentrations (>100 μg per plug) of 4‐(hydroxymethyl)‐quinoline were needed. Both metabolites revealed weak inhibition of Rhizoctonia solani. Furthermore, both compounds showed a growth promotion activity on canola (Brassica napus) seedlings used as bioassays. Conclusions: Isolation and characterization of the main secondary metabolites from culture filtrates of a root‐inhabiting sterile fungus are reported. The biological assays indicate that these secondary metabolites may have a role in both plant growth regulation and antifungal activity. Significance and Impact of the Study: This study provides a better understanding of the metabolism of a cortical fungus that may have a useful role in the biological suppression of root‐infecting soil‐borne plant pathogens.