Agronomic Practices Shape Tissue-Specific Antioxidant Capacity and Metabolic Profiles in Achillea millefolium L.

Role of ACC deaminase-producing rhizobacteria in alleviation of water stress in watermelon

Arbuscular mycorrhiza (AM), plant growth promoting rhizobacteria (PGPRs) and root-knot nematode survive in the rhizosphere and perform the same niche. AM and PGPRs play positive role in roots while nematode oppose it. Nematode damages the root system, which reduces the nutrient uptake specially phosphorus (P) while AM help to uptake. PGPRs are another symbiotic micro-organism helpful to mycorrhizal survival and colonization. AM and PGPRs can defeat the soil borne diseases like root-knot disease which lead to increasing mycorrhizal colonization and nutrient uptake. On this basis current work emphasizes the effects on mycorrhizal colonization and P uptake in presence of PGPRs along with root-knot nematode infection in tomato plants.

Effects of Plant Growth-Promoting Rhizobacteria and N Source on Plant Growth and N and P Uptake by Tomato Grown on Calcareous Soils

Earlier plant growth promoting rhizo-bacteria (PGPRs) were isolated from the plants, by cultivation based techniques and the interaction was mostly thought to be bilateral. The routine bilateral study, with no information on the associated microbiome, could be one of the reasons for the limited success of PGPRs in the field conditions. Keeping in view the role of PGPRs in rhizo-bacteriome on the growth and production of plant, the present study was aimed at studying the diversity of the rhizo-bacteriome of saffron grown across three geographical locations namely Kashmir, Kishtwar and Bengaluru. Variation in the rhizo-bacteriome of saffron growing across 10 different sites from 3 geographical locations was studied using 16S rDNA amplicon metagenomic sequencing. 16 bacterial phyla, 261 genera and 73 bacterial species were cataloged from all the rhizosphere samples. Proteobacteria was a dominant phylum in all the rhizosphere samples. Rhizo-bacteriome of saffron grown in Kishtwar was found to be significantly different from the rhizo-bacteriome of saffron grown in Kashmir and Bengaluru. Interestingly, the rhizo-bacteriome of saffron grown in Bengaluru was very similar to the saffron grown in Kashmir, thereby indicating that the rhizo-bacteriome in saffron is “plant driven” as the corm sown in Bengaluru were from Kashmir. Despite variation in rhizo-bacteriome, core rhizo-bacteriome in saffron was identified that was represented by 53 genera and eight bacterial species belonging to 11 phyla irrespective of their geographical distribution. In addition, 21 PGPRs were reported for the first time from the saffron rhizosphere. The high yielding saffron field Wuyan was found to have the highest number of PGPRs; this indicates that the presence of PGPR is important for yield enhancement than diversity. The two PGPR Rhizobium leguminosarum and Luteibacter rhizovicinus were reported from all the locations except Kishtwar that had escaped isolation in our previous attempts using cultivation based techniques. It is being proposed instead of going for random isolation and screening for PGPRs from plant rhizosphere, an alternate strategy using metagenomic cataloging of the rhizo-bacteriome community and cultivation of the dominant PGPR should be undertaken. This strategy will help in the selection of dominant PGPRs, specific to the plant in question.

Soil salinity is a serious threat to sustainable agriculture, and a number of research are going on to improve saline-resistant crops by using various breeding methods and genetic engineering tools. These methods are time-consuming, often face yield penalties, and many other ethical issues. There is a need to explore other more stable, environmentally friendly methods for the sustainable agriculture. Exploration of plant growth-promoting rhizobacteria (PGPR) associated with salt-tolerant plants (halophytes) and their use as probiotics for saline soil agriculture are a promising substitute for classical approaches. Salinity is one of the major abiotic stress reported from arid and semiarid regions which causes a major loss in the agriculture productivity. Halophytes are adapted to the saline environment because of their genetic makeup and associated microbiome. These microbiomes have potential to survive in the saline condition, but they are not thoroughly explored. Several studies showed that bacteria associated with halophytes, directly and indirectly, support the plant growth and yield in saline conditions; thus, these bacteria can be used as probiotics for salt-sensitive plants (glycophytes) grown in the salt-affected area to enhance the productivity. PGPR induce many morphological, physiological, and genetic changes in a plant which compensate the pressure of salt stress. The genetic level changes in plants due to application or the presence of PGPR are known as induced systemic resistance (ISR). PGPR secrete some beneficial elements like organic solutes, siderophores, etc. to survive in harsh conditions. PGPR also help plants to maintain their osmotic pressure and nutrient balance. The presence of PGPR also affects the level of various phytohormones in plants which play a major role in growth, development, and stress response of the plant.

The molecular and physiological mechanisms activated in plants during drought stress tolerance are regulated by several key genes with both metabolic and regulatory roles. Studies focusing on crop gene expression following plant growth-promoting rhizobacteria (PGPR) inoculation may help understand which bioinoculant is closely related to the induction of abiotic stress responses. Here, we performed a meta-analysis following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to summarise information regarding plant-PGPR interactions, focusing on the regulation of nine genes involved in plant drought stress response. The literature research yielded 3,338 reports, of which only 41 were included in the meta-analysis based on the chosen inclusion criteria. The meta-analysis was performed on four genes (ACO, APX, ACS and DREB2); the other five genes (ERD15, MYB, MYC, acdS, WRKY) had an insufficient number of eligible articles. Forest plots obtained through each meta-analysis showed that the overexpression of ACO, APX, ACS and DREB2 genes was not statistically significant. Unlike the other genes, DREB2 showed statistically significant results in both the presence and absence of PGPR. Considering I2>75 %, the results showed a high heterogeneity among the studies included, and the cause for this was examined using subgroup analysis. Moreover, the funnel plot and Egger's test showed that the analyses were affected by strong publication bias. This study argues that the presence of PGPR may not significantly influence the expression of drought stress response-related crop genes. This finding may be due to high heterogeneity, lack of data on the genes examined, and significant publication bias.

Not Just Sweet Talkers

Temperature is one of the major factors are being controlling and/or limiting growth and development of plants. The effect of plant growth promoting rhizobacteria (PGPR) (mixture of Azospirillum lipoferum, Paenibacillus polymyxa and Bacillus circulans), mycorrhizae (AM) and foliar application with glycine betaine (GB) at 0, 10 &15mmol/L individually or in combination on some growth aspects, photosynthetic pigments, microbial activities, minerals and some bioconstituents, endogenous phytohormones, flowering, fruiting and fruit quality of sweet pepper cv. California wander was studies during 2011 and 2012 seasons under open field at high temperature condition. Results indicated that, different applied treatments significantly increased most growth parameters as number of branches and leaves per plant, leaf area per plant, leaves and shoot dry weight per plant and leaf area ratio as well. Furthermore, photosynthetic pigments, NPK, total sugars and total free amino acids concentration in leaves recoded the maximum values when plants treated with PGPR, AM and foliar application with GB at 10 mmol/L as compared with those of individual application or untreated ones. Moreover, individual application with PGPR, AM and / or GB at 10 mmol/L enhanced the microbial activities in rhizosphere of the pepper plants compared with untreated ones. Also, biofertilizers and GB treatments increased auxin, gibberellin and cytokinin levels in sweet pepper shoots at 65 days after transplanting during 2012 season whereas abscisic acid was decreased. Moreover, the highest early and total yield were obtained when plants were sprayed with GB at 10 mmol/L and treated with microbial consortium (PGPR & AM). In addition, chemical composition of minerals and some bioconstituents such as total carbohydrates, vitamin C, total soluble solids in sweet pepper fruits were also increased at the same treatments. Hence, it could be recommended that foliar application with GB at 10 mmol/L in the presence of PGPR and AM as biofertilizers can be used to increase yield and fruit quality of sweet pepper plant when grown at high temperature condition.

The use of nanofertilizers has the potential to be used to enrich edible organs with nutrients (biofortification) and improve the biosynthesis of bioactive compounds and their antioxidant capacity. Therefore, the objective of this study was to evaluate the effect of biofortification with magnesium (Mg) nanofertilizer on the accumulation of bioactive compounds and antioxidant capacity in green bean cv. Strike compared to a conventional fertilizer (Mg sulfate). Two sources of Mg were applied via foliar: Nanofertilizer and Mg Sulfate at doses of 0, 50, 100, 200, and 300 mg/L of Mg. The accumulation of total polyphenols, flavonoids, anthocyanins, bioactive compounds, and antioxidant capacity was evaluated in pods. The results obtained in this research confirm the effect of green bean pods biofortified with Mg nanofertilizers on the production and accumulation of bioactive compounds and antioxidant capacity, improving the nutrition and nutraceutical quality of green beans. The 50 mg/L dose of Mg nanofertilizer was the most effective treatment to increase bioactive compounds and antioxidant capacity compared to high doses of Mg sulfate (300 mg/L). This is one of the first studies focused on biofortification with Mg nanofertilizers and their effect on the nutraceutical quality of green beans.

Because of swift climate change, drought is a primary environmental factor that substantially diminishes plant productivity. Furthermore, the increased use of chemical fertilizers has given rise to numerous environmental problems and health risks. Presently, there is a transition towards biofertilizers to enhance crops' yield, encompassing medicinal and aromatic varieties. This study aimed to explore the impacts of plant growth-promoting rhizobacteria (PGPR), both independently and in conjunction with arbuscular mycorrhizal fungi (AMF), on various morphological, physiological, and phytochemical characteristics of Dracocephalum kotschyi Boiss. This experimentation took place under different irrigation conditions. The irrigation schemes encompassed well watering (WW), mild water stress (MWS), and severe water stress (SWS). The study evaluated the effects of various biofertilizers, including AMF, PGPR, and the combined application of both AMF and PGPR (AMF + PGPR), compared to a control group where no biofertilizers were applied. The findings of the study revealed that under water-stress conditions, the dry yield and relative water content of D. kotschyi Boiss. experienced a decline. However, the application of AMF, PGPR, and AMF + PGPR led to an enhancement in dry yield and relative water content compared to the control group. Among the treatments, the co-application of AMF and PGPR in plants subjected to well watering (WW) exhibited the tallest growth (65 cm), the highest leaf count (187), and the most elevated chlorophyll a (0.59 mg g-1 fw) and b (0.24 mg g-1 fw) content. Regarding essential oil production, the maximum content (1.29%) and yield (0.13 g plant -1) were obtained from mild water stress (MWS) treatment. The co-application of AMF and PGPR resulted in the highest essential oil content and yield (1.31% and 0.15 g plant-1, respectively). The analysis of D. kotschyi Boiss. essential oil identified twenty-six compounds, with major constituents including geranyl acetate (11.4-18.88%), alpha-pinene (9.33-15.08%), Bis (2-Ethylhexyl) phthalate (8.43-12.8%), neral (6.80-9.32%), geranial (9.23-11.91%), and limonene (5.56-9.12%). Notably, the highest content of geranyl acetate, geranial, limonene, and alpha-pinene was observed in plants subjected to MWS treatment following AMF + PGPR application. Furthermore, the co-application of AMF, PGPR, and severe water stress (SWS) notably increased the total soluble sugar (TSS) and proline content. In conclusion, the results indicate that the combined application of AMF and PGPR can effectively enhance the quantity and quality of essential oil in D. kotschyi Boiss., particularly when the plants are exposed to water deficit stress conditions.

Drought is one of the major constraints limiting agricultural production worldwide and is expected to increase in the future. Limited water availability causes significant effects to plant growth and physiology. Plants have evolved different traits to mitigate the stress imposed by drought. The presence of plant growth-promoting rhizobacteria (PGPR) could play an important role in improving plant performances and productivity under drought. These beneficial microorganisms colonize the rhizosphere of plants and increase drought tolerance by lowering ethylene formation. In the present study, we demonstrate the potential to improve the growth of velvet bean under water deficit conditions of two different strains of PGPR with ACCd (1-Aminocyclopropane-1-Carboxylate deaminase) activity isolated from rainfed farming system. We compared uninoculated and inoculated plants with PGPR to assess: a) photosynthetic performance and biomass; b) ACC content and ethylene emission from leaves and roots; c) leaf isoprene emission. Our results provided evidence that under drought conditions inoculation with PGPR containing the ACCd enzyme could improve plant growth compared to untreated plants. Ethylene emission from roots and leaves of inoculated velvet bean plants was significantly lower than uninoculated plants. Moreover, isoprene emission increased with drought stress progression and was higher in inoculated plants compared to uninoculated counterparts. These findings clearly illustrate that selected PGPR strains isolated from rainfed areas could be highly effective in promoting plant growth under drought conditions by decreasing ACC and ethylene levels in plants.

Suboptimal root zone temperatures (RZT) can cause considerable stress to plant growth, especially leguminous plants such as soybean [Glycine max (L.) Merr.]. Cool root zone temperatures impair the ability of plants to acquire nutrients, decrease root and shoot growth, and affect legume nodulation and nitrogen fixation. Plant growth-promoting rhizobacteria (PGPR) are a specific group of microorganisms that can colonize plant roots and stimulate plant growth and development. PGPR can increase early season nodulation and total seasonal nitrogen fixation and yield of soybean growing in an area with cool spring soils. The ability of PGPR to stimulate soybean nodulation and growth was shown to be related to their ability to colonize soybean roots, and this was shown to be related to RZT. All steps in early nodulation were stimulated by the presence of PGPR. The beneficial effects of PGPR are exerted through a diffusible molecule excreted into the growth medium. The addition of genistein, a plant-to-bacteria signal molecule, already shown to stimulate soybean N2 fixation at low RZT, plus PGPR causes increases in soybean nodulation, N2 fixation, and growth that were greater than those caused by the addition of PGPR alone, but only at 25 and 17.5 °C, and not at 15 °C RZT.

Mutagenicity is a key biological effect environmental contaminants may exert.In our examinations groundwater samples -originating mainly from cereal fields -were analyzed.Mutagenicity was determined by application of the somatic mutation and recombination test (SMART).The test utilizes Drosophila melanogaster females carrying mwh (multi wing hair) and males carrying flr (flare) recessive marker mutations.Homozygote mwh cells grow 3-7 hairs in bundles, while flr homozygote cells form a single curly hair.Treated larvae derive from the hybridization of such parents.Larvae surviving the exposition of mutagens and developing into imagoes have possible mosaic patches on wings.As a new approach towards the practical application of the SMART test, the first step was to survey most frequent pesticides in Hungarian ground water samples.In parallel, aquatic toxicity biotests were carried out using the Daphina magna Straus.The most contaminated water samples, containing residues of acetochlor, atrazine, diazinon, metolachlor, terbutryn and/or trifluralin at levels of 0.18 to over 1000 ng ml -1 showed acute toxicity in the Daphnia magna test, but no mutagenic effect (mutation frequency was <10 -4 ) in the SMART test.

ABSTRACTThe present attempt was made to determine the effects of untreated municipal wastewater (MW) on growth and physiology of maize and to evaluate the role of Ag nanoparticle and plant-growth-promoting rhizobacteria (PGPR) when interacting with MW used for irrigation. It was used for the isolation of PGPR. The isolates were identified and characterized based on the colony morphology, C/N source utilization pattern using miniaturized identification system (QTS 24), catalase (CAT) and oxidase tests, and 16S rRNA sequence analyses. The three PGPR isolates were Planomicrobium chinense (accession no. NR042259), Bacillus cereus (accession no. CP003187) and Pseudomonas fluorescens (accession no. GU198110). The isolates solubilized phosphate and exhibited antibacterial activities against pathogenic bacteria i.e., Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis, Klebsiella pneumoniae and Escherichia coli and antifungal activities against Helminthosporium sativum and Fusarium solani. The untreated MW irrigation as well as Ag nanoparticle treatment resulted in significant accumulation of Ni in the rhizosphere soil. PGPR induced accumulation of Ni and Pb in the rhizosphere soil and maize shoot. Ag nanoparticle also caused Ni and Pb accumulation in maize shoot. Combined treatment with PGPR, Ag nanoparticle and MW resulted in decreased accumulation of Pb and Ni both in the rhizosphere soil and maize shoot. Combined treatment of Ag nanoparticle, MW and PGPR decreased Na accumulation and increased K accumulation. Ag nanoparticle increased Fe and Co accumulation but decreased Zn and Cu accumulation in MW treatment; in combined treatment, it reduced PGPR-induced accumulation of Co and Fe in the rhizosphere and Co accumulation in shoot. PGPR significantly increased root weight, shoot weight, root length, shoot length, leaf area, and proline, chlorophyll and carotenoid content of the maize plant. Ag nanoparticle also enhanced the leaf area, fresh weight, root length and antioxidant activities of maize. Treatment with Ag nanoparticle increased the gibberellic acid (GA) and abscisic acid (ABA) content of maize leaves but decreased the accumulation of GA in the presence of PGPR and MW.

Application of Zn-containing foliar fertilisers for recovery of the grain productivity potential of Zn-deficient maize plants