Indole-3-acetic Acid Research Articles

The MYB transcriptional factor BrMYB108 regulates Auxin-mediated delayed leaf senescence in postharvest Pak Choi

Auxin is the earliest discovered class of endogenous plant hormones, widely distributed in higher plants, and plays a key role in regulating plant growth and development. However, the molecular mechanism by which auxin affects postharvest leaf senescence in pak choi (Brassica rapa subsp. chinensis) remains unclear. In this study, we found that exogenous application of 2 mg L−1 of the auxin analog indoleacetic acid (IAA) could delay postharvest leaf senescence in pak choi. Importantly, we isolated an R2R3-MYB transcription factor (TF), BrMYB108, which was highly expressed in senescent leaves and whoes expression was suppressed by IAA treatment. Molecular evidence confirmed that BrMYB108 can bind to the promoter region of the chlorophyll metabolism gene BrSGR2 to activate its expression. Heterologous expression of BrMYB108 in Arabidopsis accelerated leaf senescence, while silencing BrMYB108 in pak choi using virus induced gene silencing (VIGS) delayed leaf senescence. In addition, we found that BrMYB108 is a direct target gene of the auxin response factor 17 (ARF17) homolog gene, BrARF17, in Arabidopsis. Our study reveals a model in which BrARF17 regulates postharvest leaf senescence in pak choi by targeting the expression of BrMYB108. These molecular insights into the auxin-mediated regulation of postharvest leaf senescence in pak choi have positive implications for manipulating BrMYB108 to improve the postharvest shelf life of vegetables.

Characterization of Sinorhizobium strains isolated from arid and semi-arid areas of Morocco promoting the growth of Vachellia gummifera

Vachellia gummifera is a nitrogen-fixing shrub endemic to Morocco, and represents a suitable candidate for reforestation programs in dry areas. In this study, we identified seven root microsymbionts of V. gummifera, and determined their phenotypic characteristics, Plant Growth-Promoting (PGP) activities and their symbiotic efficiency. The bacteria were isolated from root nodules of the plant grown in Moroccan forest soils located in arid and semi-arid regions. The 16S rRNA gene sequences analysis of seven isolates showed similarity values ranging from 99.85% to 99.92% with Sinorhizobium fredii USDA205T. The phenotypic analyses displayed that the strains use different carbohydrates, mainly mono and di-saccharides, as a sole carbon source, and 13 out of 15 amino acids tested as the sole nitrogen source. The strains have variable tolerance to heavy metals, but are sensitive to salinity and high temperature, as no one grew in the presence of 2% NaCl (w/v) or at 40 °C, respectively. On the other hand, the strains grew in a very high osmotic stress environment induced by PEG 6000 (20% w/v), and they all grow in a pH range between 6.5 and 9. The strains possess PGP activities, such as phosphate solubilization, siderophore, and indole acetic acid production. Inoculation under axenic conditions showed that the strains increased the aerial biomass of inoculated plants up to 217%, whereas the relative symbiotic efficiency percentages (74.87–140,3%) showed that most strains are very efficient. From all these results we concluded that our strains may be proposed as inoculum for large-scale applications, such as reforestation programs.

Photosynthesis, Chlorophyll Fluorescence, and Hormone Regulation in Tomato Exposed to Mechanical Wounding.

To understand the physiological responses of seedlings to mechanical wounding, we analyzed photosynthesis, chlorophyll fluorescence, and endogenous hormones in tomato (Solanum lycopersicum L.) subjected to varying levels of mechanical pressure. The results showed that, at 4 h after wounding, excess excitation energy was dissipated as thermal energy through the reduction in the photosystem II (PSII) opening degree and the increase in non-photochemical quenching. Photodamage was avoided, and stomatal closure was the most prominent factor in photosynthesis inhibition. However, 12 h after wounding, the photoprotective mechanism was insufficient to mitigate the excess excitation energy caused by the wound, leading to photochemical damage to physiological processes. Meanwhile, the non-stomatal factor became the most prominent limiting factor for photosynthesis at 80 N pressure. At 12 and 36 h after wounding, the concentrations of abscisic acid (ABA), methyl jasmonate (MeJA), indole-3-acetic acid (IAA), zeatin riboside (ZR), and gibberellic acid (GA3) in the stems showed a trend towards being increased, which promoted wound healing. However, after mechanical wounding, the ratio of stress- to growth-promoting hormones first increased and then decreased. This pattern can enhance stress resistance and promote cell division, respectively. Comprehensive analysis showed that the fluorescence parameter, photochemical quenching coefficient (Qp_Lss), was the most suitable indicator for evaluating mechanical wounding conditions.

Complete Genome of Achromobacter xylosoxidans, a Nitrogen-Fixing Bacteria from the Rhizosphere of Cowpea (Vigna unguiculata [L.] Walp) Tolerant to Cucumber Mosaic Virus Infection.

Achromobacter xylosoxidans is one of the nitrogen-fixing bacteria associated with cowpea rhizosphere across Africa. Although its role in improving soil fertility and inducing systemic resistance in plants against pathogens has been documented, there is limited information on its complete genomic characteristics from cowpea roots. Here, we report the complete genome sequence of A. xylosoxidans strain DDA01 isolated from the topsoil of a field where cowpea plants tolerant to cucumber mosaic virus (CMV) were grown in Ibadan, Nigeria. The genome of DDA01 was sequenced via Illumina MiSeq and contained 6,930,067 nucleotides with 67.55% G + C content, 73 RNAs, 59 tRNAs, and 6421 protein-coding genes, including those associated with nitrogen fixation, phosphate solubilization, Indole3-acetic acid production, and siderophore activity. Eleven genetic clusters for secondary metabolites, including alcaligin, were identified. The potential of DDA01 as a plant growth-promoting bacteria with genetic capabilities to enhance soil fertility for resilience against CMV infection in cowpea is discussed. To our knowledge, this is the first complete genome of diazotrophic bacteria obtained from cowpea rhizosphere in sub-Saharan Africa, with potential implications for improved soil fertility, plant disease resistance, and food security.

The effects of humic substances application on the phytohormone profile in Lactuca sativa L.

AbstractHumic substances (HS) are commonly employed as plant biostimulants to enhance crop yields. However, the HS mechanisms of action, as well as the differences between radicular and foliar modes of application, remain unclear. Here, we explored the changes in phytohormonal balance as possible mechanism of HS to enhance lettuce (Lactuca sativa L.) growth, and the difference between both modes of application. For this purpose, BLACKJAK®, a HS‐based product was applied as radicular (R) and foliar (F) at the concentrations (mL/L): 0.20 (R1), 0.40 (R2), 0.60 (R3), 0.80 (R4), 5.00 (F1), 7.50 (F2), 10.00 (F3), and 12.50 (F4). The experiment was performed in pots filled with vermiculite:perlite (3:1) and HS were applied three times with a periodicity of 10 days. Shoot and root growth parameters were measured. In addition, the phythormones indole‐3‐acetic acid (IAA), gibberellins (GAs), trans‐zeatine (tZ), isopentenyl adenine (iP), 1‐aminocyclopropane‐1‐carboxylic acid (ACC), abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA), were analysed by U‐HPLC‐MS. BLACKJAK® application resulted in higher shoot growth at doses R1, R2, R3, F2, and F3, whereas root biomass was increased at R2, R3, F2, F3, and F4, showing radicular better plant growth than foliar applications. Furthermore, HS changed phytohormonal balance in shoots and roots. However, it was with radicular applications, especially at R2, where phytohormonal profile was best associated with plant growth due to the increases observed in IAA, GAs, JA, SA, tZ, and decreased ABA. However, further research is needed to clarify the involvement of hormones in the growth‐promoting action of HS.

Biocontrol of fungal pathogens and growth promotion in the Korean fir (Abies koreana E.H.Wilson) seedling using Bacillus velezensis CE 100

The restoration of the endangered Korean fir (Abies koreana E.H.Wilson) forests requires mass production of high-quality and well-developed seedlings for outplanting. However, phytopathogenic fungal infections lower the survival rate and growth vigor of A. koreana seedlings, frustrating the re-afforestation efforts. This study isolated and identified the phytopathogenic fungi causing seedling blight and wilt diseases in A. koreana seedlings and investigated the potential of Bacillus velezensis CE 100 in controlling the fungal pathogens and promoting seedling growth. Phomopsis mali and Fusarium oxysporum were confirmed as the causal agents of blight and wilt diseases, respectively, and both fungi reduced the survival rate of A. koreana seedlings. B. velezensis CE 100 produced cell wall-degrading enzymes: chitinase, protease, and β-1,3-glucanase, and the bacterial crude enzyme fraction inhibited the spore germination and mycelial growth of P. mali and F. oxysporum in a concentration-dependent manner, causing severe morphological deformations. Consequently, treatment with B. velezensis CE 100 improved the survival rate of seedlings infected with either P. mali or F. oxysporum compared to the control and PB media treatment. The bacterium also increased nutrient availability through ammonia–nitrogen production and phosphate solubilization and produced indole-3-acetic acid (IAA), and its inoculation remarkably improved seedling growth (root and shoot dry weight) compared to the control and PB media treatment group. This is the first study to report P. mali and F. oxysporum as the pathogens causing seedling blight and wilt diseases in A. koreana nursery seedling, and the possibility of using B. velezensis CE 100 to control the fungal pathogens and improve the seedling growth without chemical use.

Citrus Fruits Produce Direct Defense Responses against Oviposition by Bactrocera minax (Diptera: Tephritidae).

Plants perceive and orchestrate defense responses when herbivorous insects are ovipositing. Fruits, as a crucial reproductive organ in plants, have rarely been researched on the responses to insect eggs. Here, we found that oviposition by the specialist insect Bactrocera minax in navel oranges activated the lignin synthesis pathway and cell division, causing mechanical pressure that crushed the eggs. Transcriptome and metabolome analyses revealed an enrichment of oviposition-induced genes and metabolites within the lignin synthesis pathway, which was confirmed by histochemical staining. Furthermore, hydrogen peroxide (H2O2) accumulation was observed at the oviposition sites. Plant defense-related hormones jasmonic acid (JA) and salicylic acid (SA) exhibited rapid induction after oviposition, while indole-3-acetic acid (IAA) activation occurred in the later stages of oviposition. Additionally, secondary metabolites induced by prior egg deposition were found to influence larval performance. Our studies provide molecular evidence that host fruits have evolved defense mechanisms against insect eggs and pave the way for future development of insect-resistant citrus varieties.

Effects of Plant Growth Promoting Halotolerant Pseudomonas Aeruginosa JCM 5962 with Hydrocarbon Degradation Ability, Isolated from Sundarbans Mangrove Area in West Bengal, on Abelmoschus esculentus (Okra) Plant Growth

Plant growth promoting rhizobacteria (PGPR) play a key role in sustainable agricultural practices leading to increased crop productivity. Moreover, PGPR with ability to diminish abiotic stresses like salinity and hydrocarbon contamination in soil, can be developed into potent biofertilizers with maximum ecological benefits. Sundarbans mangrove region in West Bengal, a natural reservoir of diverse microbiota is an important source of PGPR adapted to high salinity and other abiotic stresses like hydrocarbon contamination due to oil spillage and water transport systems, rendering the soil unsuitable for farming. In the present study, a potent PGPR has been isolated from rhizospheric soil of Matla riverbed in mangrove areas of Sundarbans, with simultaneous nitrogen fixing, phosphate solubilizing and plant hormone like indole acetic acid (IAA) producing properties as well as high salt tolerance and hydrocarbon bioremediation abilities. The strain has been identified as Pseudomonas aeruginosa JCM 5962 (NCBI Accession number MK544832.1) on the basis of 16S rRNA analysis. The isolated Pseudomonas aeruginosa strain showed atmospheric nitrogen fixation (3612 ± 2 mg N/ Kg of soil), highest phosphate solubilization index of 3.0 ± 0.06 and 37.14 µg/mL of IAA production. This potent strain also showed salt tolerance upto 7% in culture broth and an uptake of 18.72% of salt. Highest hydrocarbon degradation was shown by this strain in presence of diesel as the sole carbon source. The isolated Pseudomonas aeruginosa strain showed overall improvement in growth of Abelmoschus esculentus (Okra) plants in pot experiments in different conditions like absence of any abiotic stress, presence of 5% salt stress and presence of 1% diesel contaminant. These results indicate that Pseudomonas aeruginosa JCM 5962 can be developed as a potent biofertilizer to be used in agricultural lands of Sundarbans mangrove regions and other areas which are plagued by high salinity and increasing hydrocarbons, particularly petroleum contamination.

Multi-metal tolerant Porostereum umbrinoalutaceum isolated from Pleurotus ostreatus fruit body showing root colonization, growth promotion of chilli (Capsicum annuum L.) plant and antagonism against fungal pathogens.

Mushroom associated microbes could be utilized to improve crop productivity providing nutrients, plant growth promoting substances, production of hydrolytic enzymes and protecting plant from biotic and abiotic stress. An endophyte designated as KUFC101 was isolated from fruit body of Pleurotus ostreatus and identified as Porostereum umbrinoalutaceum based on nuclear-rRNA gene sequence analysis. Growth in different culture media, metal tolerance, biochemical characterization and effect on chilli plant growth promotion were studied. The isolate showed best growth in Malt extract medium and least growth in synthetic media. It could tolerate toxic metals (Mg, Ca, Fe, Cu, Mn, Zn and Cd each at 100ppm concentration). It produced amylase, cellulase, chitinase, pectinase, catecholate type of siderophore and indole acetic acid, and inhibited growth of Alternaria solani and Penicillium citrinum. It could colonize in the rhizosphere of chilli plant and influence growth of chilli plant by improving biomass and metabolite content. Porostereum umbrinoalutaceum KUFC101 could be utilized in formulation of biofertiliser under sustainable agricultural system.

Endogenous phytohormone analysis during sequential stages of somatic embryogenesis in Musa AAA cv. Grand Naine (subgroup Cavendish)

Abstract This is the first initiative study to provide quantified levels of four endogenous phytohormones during the induction, regeneration, maturation and germination stages of somatic embryogenesis (SE) in banana, using immature male bud explants, in the popular commercial triploid cultivar Grand Naine (AAA). Phytohormones are known to play a major role in the regulation of SE and most protocols have been developed for various cultivars of banana following empirical approaches. Although, several reports are available with regard to the impact of growth regulators exogenously supplemented to the media, the vital role of endogenous growth hormones in various developmental stages of SE remain unclear in banana. Reverse Phase High Performance Liquid Chromatography (RP-HPLC) was used to analyze endogenous status of indole acetic acid (IAA), zeatin, gibberellic acid (GA) and abscisic acid (ABA). Results from this study revealed that endogenous IAA and GA along with exogenous auxin play a major role in the induction of embryogenic competence of male bud explants. The levels of endogenous IAA and zeatin were found to be higher in embryogenic calli than non-embryogenic calli, although three different types of exogenous auxins were supplemented in callogenesis medium, but not cytokinin. Higher level of ABA and GA was observed in early and late developmental stages of somatic embryo, respectively. GA also played a predominant role in germination of somatic embryos. These findings will be applied for improvement of SE protocol in recalcitrant banana cultivars by suitably altering or supplementing exogenous growth hormones.

An EIL Family Transcription Factor From Switchgrass Affects Sulphur Assimilation and Root Development in Arabidopsis.

Sulphur limitation 1 (SLIM1), a member of ethylene-insensitive3-like (EIN3/EIL) protein family, is recognised as the pivotal transcription factor regulating sulphur assimilation, essential for maintaining sulphur homoeostasis in Arabidopsis. However, the function of its monocot homologues is largely unknown. In this study, we identified PvEIL3a, a homologous gene of AtSLIM1, from switchgrass (Panicum virgatum L.), a significant perennial bioenergy crop. Our results demonstrated that introducing PvEIL3a into Arabidopsis slim1 mutants significantly increased the expression of genes responsive to sulphur deficiency, and transgenic plants exhibited shortened root length and delayed development. Moreover, PvEIL3a activated the expression of AtAPR1, AtSULTR1;1 and AtBGLU30, which plays an important role in sulphur assimilation and glucosinolate metabolism. Results of transcriptome and metabonomic analysis further indicated a perturbation in the metabolic pathways of tryptophan-dependent indole glucosinolates (IGs), camalexin and auxin. In addition, PvEIL3a conservatively regulated sulphur assimilation and the biosynthesis of tryptophan pathway-derived secondary metabolites, which reduced the biosynthesis of indole-3-acetic acid (IAA) and inhibited the root elongation of transgenic Arabidopsis. In conclusion, this study highlights the functional difference of the ethylene-insensitive 3-like (EIL) family gene in monocot and dicot plants, thereby deepening the understanding of the specific biological roles of EIL3 in monocot plant species.

Soil and root microbiome analysis and isolation of plant growth-promoting bacteria from hybrid buffaloberry (Shepherdia utahensis 'Torrey') across three locations.

The effects of climate change are becoming increasingly hazardous for our ecosystem. Climate resilient landscaping, which promotes the use of native plants, has the potential to simultaneously decrease the rate of climate change, enhance climate resilience, and combat biodiversity losses. Native plants and their associated microbiome form a holo-organism; interaction between plants and microbes is responsible for plants' growth and proper functioning. In this study, we were interested in exploring the soil and root microbiome composition associated with Shepherdia utahensis, a drought hardy plant proposed for low water use landscaping, which is the hybrid between two native hardy shrubs of Utah, S. rotudifolia and S. argentea. The bulk soil, rhizosphere, root, and nodule samples of the hybrid Shepherdia plants were collected from three locations in Utah: the Logan Campus, the Greenville farm, and the Kaysville farm. The microbial diversity analysis was conducted, and plant growth-promoting bacteria were isolated and characterized from the rhizosphere. The results suggest no difference in alpha diversity between the locations; however, the beta diversity analysis suggests the bacterial community composition of bulk soil and nodule samples are different between the locations. The taxonomic classification suggests Proteobacteria and Actinobacteriota are the dominant species in bulk soil and rhizosphere, and Actinobacteriota is solely found in root and nodule samples. However, the composition of the bacterial community was different among the locations. There was a great diversity in the genus composition in bulk soil and rhizosphere samples among the locations; however, Frankia was the dominant genus in root and nodule samples. Fifty-nine different bacteria were isolated from the rhizosphere and tested for seven plant growth-promoting (PGP) traits, such as the ability to fix nitrogen, phosphates solubilization, protease activity, siderophore, Indole Acetic Acid (IAA) and catalase production, and ability to use ACC as nitrogen source. All the isolates produced some amount of IAA. Thirty-one showed at least four PGP traits and belonged to Stenotrophomonas, Chryseobacterium, Massilia, Variovorax, and Pseudomonas. We shortlisted 10 isolates that showed all seven PGP traits and will be tested for plant growth promotion.

Enhancing Soybean Growth with Phytohormone-enriched PGPR Bioinoculants and Biofertilizers in Plant Stress Physiology

Background: The present investigation aimed to evaluate the effects of plant growth-promoting rhizobacteria (PGPR) bioinoculants and their carrier-based biofertilizers on the physiology of soybean. Methods: Seeds of two soybean varieties (cv. NARC-1 and cv. William-82) were either soaked in broth cultures of two PGPR strains, Planomicrobium chinense (MF616408) and Pseudomonas putida (KX574857), containing 106 cells/mL, or coated with biofertilizers. Three biofertilizers, namely biostimulant, biozote and biofert, were used. Result: Significant increases in root and shoot weight were observed with both liquid bioinoculants and carrier-based biofertilizers compared to the control. The consortium of P. chinense and P. putida resulted in the highest proline content and superoxide dismutase (SOD) activity. Biostimulant-treated plants exhibited higher catalase (CAT) activity and phenolics content. Indole-3-acetic acid (IAA) and gibberellic acid (GA) levels were enhanced in plants treated with PGPR and biofertilizers. Specifically, P. chinense and the biostimulant significantly promoted IAA content in cv. William-82, while biozote and P. chinense treatments increased GA content in both varieties. The consortium of P. chinense and P. putida showed the lowest ABA levels. The highest IAA/ABA and GA/ABA ratios were observed in plants treated with P. chinense. Liquid bioinoculants had a more pronounced effect on plant growth than carrier-based biofertilizers, though biofertilizers had stronger residual effects on rhizosphere soil organic matter. The combined effects of phytohormones, sugar, protein and proline production and antioxidant enzyme activity influenced plant growth and development.

Physiological Age of Stock Plants Determines Phytohormonal Changes in Leafy Cuttings of Prunus subhirtella 'Autumnalis'

AbstractThe aim of this study was to investigate adventitious root formation in cuttings obtained from physiologically different old stock material. The ornamental cherry Prunus subhirtella ´Autumnalis´ was used for the experiment. We examined three stock plants, namely a physiologically mature stock plant (about 60 years old) and physiologically juvenile plants (21 years old), which were previously propagated by cuttings, semi-mature stock material and in vitro juvenile stock material. We also investigated the role of phytohormones in the induction phase of adventitious root (AR) formation depending on the physiological age of the stock plant and the time after cutting. High performance liquid chromatography coupled with mass spectrometry (HPLC–MS/MS) was used to identify and quantify the phytohormones. The difference in rooting and quality of the developed AR is observed between semi-mature stock and mature stock material. Cuttings from semi-mature plants rooted in 95.00% of cases, while cuttings from mature stock plants only rooted in 68.33%. The high concentration of strigolactones and jasmonic acid (JA) immediately after severance had an inhibitory effect on the development of adventitious roots, especially in cuttings of mature origin. The development of AR is positively influenced by the increase in indole-3-acetic acid (IAA) 4 h after cutting from the stock plant. Our results show that the formation of adventitious root formation depends on the concentration and ratio between different phytohormones.

Rhizobial and passenger endophytes alleviates moisture stress in groundnut (Arachis hypogaea)

Moisture stress poses a significant threat to global agriculture, compromising crop yields and food security. In the quest for sustainable solutions, endophytic microorganisms have emerged as promising candidates for enhancing plant resilience to drought. The study's primary goal was to analyse the significance of bacterial endophytes, both rhizobial and passenger endophytes, in alleviating the effects of moisture stress. Here, PEG 6000 was used to test the drought endurance of the ten identified rhizobial and passenger endophytes. Rhizobium pusense S6R2, Enterobacter cloacae S23 and Bacillus tequilensis NBB13 were selected as best performing endophytes as they showed high tolerance of poly ethylene glycol (PEG) and maximum plant growth promoting traits like Indole Acetic Acid, exopolysaccharide production, biofilm formation, 1-aminocyclopropane1-carboxylate (ACC) deaminase activity, siderophore, zinc and phosphorous solubilisation even in PEG induced moisture stress condition. Metabolite analysis revealed that twenty-four significant compounds mostly belong to fatty acyls, amino acids, peptides, polyketides, and benzenoids were found in the root exudates of groundnut treated with endophytes. The best-performing endophytes were used in a pot culture experiment, with groundnut as the test crop. The current study found that co-inoculation of Rhizobium pusense S6R2 and Enterobacter cloacae S23 significantly increased nodule number, growth, photosynthetic pigment, anti-oxidant enzymes, and osmolyte under moisture stressed conditions when compared to other treatments. As a result, co-inoculation of Rhizobium and entophytic bacteria may be recommended as a bio-inoculant for groundnut for moisture stress alleviation after confirming the results in field evaluation.

Enhancing Growth in Vigna radiata through the Inhibition of Charcoal Rot Disease: A Strategic Approach Using Plant Growth-Promoting Rhizobacteria.

Macrophomina phaseolina is a vital seed and soil-borne phytopathogen responsible for substantial crop yield losses. Although various methods exist for managing soil-borne pathogens, such as agronomic practices, chemical treatments, and varietal tolerance, biological control utilizing plant growth-promoting rhizobacteria (PGPR) or their secondary metabolites presents promising avenues. In this study, a screening of 150 isolates from the rhizosphere of Vigna radiata L. was conducted to identify strains capable of promoting host growth and controlling charcoal rot disease. Among the tested isolates, only 15 strains demonstrated the ability to produce plant growth-related metabolites, including indole acetic acid, hydrogen cyanide, ammonia, and lytic enzymes, and solubilize inorganic phosphate. Subsequently, these potent strains were evaluated for their antifungal activity against Macrophomina phaseolina in vitro. Three strains, namely MRP-7 (58% growth inhibition), MRP-12 (55% growth inhibition), and MRP-8 (44% growth inhibition), exhibited the highest percent growth inhibition (PGI.). Furthermore, a pot experiment demonstrated that the selected strains acted as effective growth promoters and ROS (reactive oxygen species) scavengers, and served as potential biocontrol agents, significantly reducing the incidence of charcoal rot disease and improving various agronomic attributes of the host plant. These findings highlight the potential of these strains to be utilized as biofertilizers and biocontrol agents for sustainable agricultural practices.

Antagonism of rhizosphere Trichoderma brevicompactum DTN19 against the pathogenic fungi causing corm rot in saffron (Crocus sativus L.) in vitro.

Corm rot in saffron (Crocus sativus L.) significantly impacts yield and quality. Non-toxic fungi, particularly Trichoderma species, are valuable for biological control due to their production of diverse and biologically active secondary metabolites. This study aimed to isolate an effective antagonistic fungus against the pathogenic fungi causing corm rot in saffron. Four pathogenic fungi (Fusarium oxysporum, Fusarium solani, Penicillium citreosulfuratum, and Penicillium citrinum) were isolated from diseased saffron bulbs in Chongming. Initial screening through dual culture with these pathogens re-screening from rhizosphere soil samples of C. sativus based on its inhibitory effects through volatile, nonvolatile, and fermentation broth metabolites. The inhibitory effect of biocontrol fungi on pathogenic fungi in vitro was evaluated by morphological observation and molecular biology methods. Antagonistic fungi were identified as Trichoderma brevicompactum DTN19. F. oxysporum was identified as the most severe pathogen. SEM (scanning electron microscope) and TEM (transmission electron microscope) observations revealed that T. brevicompactum DTN19 significantly inhibited the growth and development of F. oxysporum mycelium, disrupting its physiological structure and spore formation. Additionally, T. brevicompactum DTN19 demonstrated nitrogen fixation and production of cellulase, IAA (Indole acetic acid), and siderophores. Whole-genome sequencing of strain DTN19 revealed genes encoding protease, cellulase, chitinase, β-glucosidase, siderophore, nitrogen cycle, and sulfate transporter-related proteins. T. brevicompactum DTN19 may inhibit the propagation of pathogenic fungi by destroying their cell walls or producing antibiotics. It can also produce IAA and iron carriers, which have the potential to promote plant growth. Overall, T. brevicompactum DTN19 showed the development prospect of biological agents.

Exogenous Melatonin Alleviates Osmotic Stress by Enhancing Antioxidant Metabolism, Photosynthetic Maintenance, and Hormone Homeostasis in Forage Oat (Avena sativa) Seedlings

Melatonin (MT) is a multifunctional hormone that enhances crop resilience against various abiotic stresses. However, its regulatory mechanism of osmotic tolerance in forage oats (Avena sativa) plants under water-limited scenarios is still unclear. This study aimed to delineate the impact of MT pretreatment on the morphological, physiological, and biochemical functions of oat seedlings under osmotic stress. Our findings demonstrated that exogenous treatment of MT noticeably elevated leaf area while decreasing the root/shoot ratio of oat seedlings subjected to osmotic stress. Osmotic-induced 38.22% or 48.37% decrease in relative water content could be significantly alleviated by MT pretreatment on day 7 or day 14, respectively. MT treatment also significantly mitigated osmotic-induced decreases in photosynthetic parameters including net photosynthetic rate, stomatic conductance, and intercellular CO2 concentration as well as various chlorophyll fluorescence parameters, which could contribute to enhanced accumulations of free proline and soluble sugars in seedlings after being subjected to a prolonged duration of osmotic stress. Furthermore, MT markedly improved antioxidant enzyme activities including superoxide dismutase, ascorbate peroxidase, catalase, and peroxidase along with the accumulation of ascorbic acid contributing to a significant reduction in reactive oxygen species under osmotic stress. In addition, the MT application induced a 978.12%, 33.54%, or 30.59% increase in endogenous MT, indole acetic acid, or gibberellic acid content under osmotic stress but did not affect the accumulation of abscisic acid. These findings suggest that an optimal concentration of MT (100 μmol·L−1) could relieve osmotic stress via improvement in osmotic adjustment, the enzymatic antioxidant defense system, and endogenous hormonal balance, thereby contributing to enhanced photosynthetic functions and growth of oat seedlings under water-limited conditions.

Agricultural Biotechnological Potential of Bacillus velezensis C3-3 and Cytobacillus sp. T106 from Resource Islands of a Semi-arid Zone of La Guajira-Colombia

Resource islands are vegetative formations in arid and semi-arid ecosystems that harbor microorganisms facing extreme conditions. However, there is a limitation in the knowledge of the agricultural biotechnological potential of microorganisms present in these islands. This study aimed to determine the capacity of Bacillus velezensis C3-3 and Cytobacillus sp. T106 isolates from resource islands to promote plant growth and control the phytopathogen Rhizoctonia solani. The bacteria were sequenced, and both grew at 50 °C, resisted 5% NaCl, withstood UV exposure, and grew in extreme pH conditions. Sixty-six genes in C3-3 and 71 in T106 were identified associated with plant growth promotion, and C3-3 was shown to promote leaf growth in lettuce plants. This promotional effect was associated with the production of indole-3-acetic acid (IAA), phosphorus solubilization, and the presence of genes related to the assimilation of rhizosphere exudates. Both strains inhibited R. solani through the production of volatile compounds and antagonism. Forty-five and 40 of these genes in C3-3 and T106, respectively, were associated with the production of proteases, lipases, siderophores, antimicrobial compounds, degradation enzymes, and secretion systems. Notably, Cytobacillus sp. has not been previously reported as a biocontrol agent. This work contributes to the evidence of the biotechnological potential of semi-arid region bacteria, offering prospects for improving agricultural production in areas with limiting conditions.

Bacillus subtilis B55 degraded the ferulic acid and p-coumaric acid and changed the soil bacterial community in soils.

This study aimed to assess the effects of phenolic acid-degrading bacteria strains on phenolic acid content, plant growth, and soil bacterial community in phenolic acid-treated soils. The strain of interest coded as B55 was isolated from cucumber root litter, and its degradation rates of ferulic acid and p-coumaric acid were 81.92% and 72.41% in Luria-Bertani solution, respectively, and B55 was identified as Bacillus subtilis. B55 had plant growth-promoting attributes, including solubilization of inorganic phosphate and production of siderophore and indole acetic acid. Both ferulic acid and p-coumaric acid significantly restrained an increase in cucumber seedling dry biomass, while the B55 inoculation not only completely counteracted the damage of phenolic acids to cucumber seedlings and decreased the content of ferulic acid and p-coumaric acid in soil, but also promoted cucumber seedlings growth. Amplicon sequencing found that B55 inoculation changed the cucumber rhizosphere bacterial community structure and promoted the enrichment of certain bacteria, such as Pseudomonas, Arthrobacter, Bacillus, Flavobacterium, Streptomyces, and Comamonas. B55 not only promoted cucumber seedling growth, and decreased the content of ferulic acid and p-coumaric acid in soil, but it also increased the relative abundance of beneficial microorganisms in the cucumber rhizosphere.