Ameliorative effects of plant growth-promoting rhizobacteria on salinity tolerance of sweet basil (Ocimum basilicum L.)

Plant growth-promoting rhizobacteria (PGPR) are important members of soil microbial communities. In this study, the effects of several PGPR on the growth of Carya illinoinensis plants, the microbial community composition and soil nutrients were investigated by inoculation tests to identify excellent PGPR strains. The experiment showed that after PGPR application, the plant height, ground diameter, and dry weight of C. illinoinensis were significantly increased compared with those of the control group, and Bacillus velezensis YH20 had the most significant effect in promoting growth (p < 0.05). In addition, all the PGPRs used for inoculation promoted plant root growth, and the Brevibacillus reuszeri MPT17 strain had the most significant promoting effect on plant root growth (p < 0.05). The application of PGPRs also affected the nutrient levels in plants and plant rhizosphere soil. For example, compared with the control, the levels of available phosphorus and potassium in rhizosphere soil and the total potassium content in plant roots were significantly increased under Br. reuszeri MPT17 treatment (p < 0.05). The experiment showed that the relative abundance of Mortierella, Dictyophora, and Bacillus in the rhizosphere soil increased significantly after the application of PGPR (p < 0.05). These genera could effectively improve the rate of soil nutrient use, antagonize plant pathogenic bacteria, and promote plant growth. This study provides basic reference data regarding the use of PGPR to improve the microecological environment and promote the growth and development of C. illinoinensis plants.

Spodopter aexigua (Hubner) is known as a cosmopolitan pest of many crops, including bunching onion. Infestation by S. exigua is often serious in tropical regions, and insecticide resistance is a major problem in the management of this pest. Treating crops with a group of naturally occurring beneficial root bacteria, termed plant growth-promoting rhizobacteria (PGPR), has been shown to increase plant growth and enhance plant health. The effects of PGPR on plant–insect interactions have been reported in very few studies. The aim of this study was to compare the effect of indigenous and nonindigenous PGPR to induce the resistance of bunching onion against S. exigua and to increase plant growth and yield. The study was designed as a field experiment at endemic area for S. exigua. Treatments were 12 indigenous rhizobacterial strains from bunching onion rhizosphere, 14 nonindigenous rhizobacterial strains from the Cyperus esculentus rhizosphere, a control (without PGPR), and an insecticide (imidacloprid). PGPR strains were inoculated on bunching onion at two periods: at the time of planting as a seedling treatment, and on 2-week-old plants as a soil drench. The randomized complete block design was replicated three times. During the experiment, the population density of S. exigua and the damage to bunching onion and its growth and yield were evaluated. Our results showed that inoculation with the indigenous rhizobacterial strains was more effective to induce the resistance of bunching onions against S. exigua and to increase the growth and yield of bunching onion compared to nonindigenous rhizobacterial strains, control, and insecticide.

As a kind of medicinal plant, Peucedanum praeruptorum Dunn has been over-harvested in the wild population, which leads to its artificial cultivation. The present study aims to analyze the effects of different plant growth-promoting rhizobacteria (PGPR) on the growth and physiological characteristics of P. Praeruptorum leaves. Compared with the CK, the content of malondialdehyde (MDA) was drastically reduced in the leaves of P. Praeruptorum in different treatment groups (P < 0.05), and with S6 showing the most significant reduction in MDA content (content was only about 1/3 that of the CK). The indicators of leaf area, length and width were found to be the highest in group S9, reaching a level that is 3.75, 3.08 and 1.48 times higher than those in group CK, respectively. Group S8 has the largest plant height, which is 1.22 times higher than that in group CK. S2 has the largest stem diameter, which is 1.69 times higher than that in group CK. Group S1 has the largest petiole length, which is 1.74 times higher than that in group CK. Group S6 has the largest chlorophyll content, which is 1.63 times higher than that in group CK. Group S2 has the highest content of soluble sugar and soluble protein, which are 2.02 times and 3.82 times higher than those in group CK. Group S9 exhibits the strongest CAT activity, which is 3.71 times higher than that in group CK. S5 exhibits the strongest SOD activity, which is 2.32 times higher than group CK. Group S1 exhibits the strongest POD activity, which is 5.94 times higher than that in group CK. In conclusion, the inoculation with PGPR is effective in improving the growth of P. Praeruptorum leaves and their physiological indicators, which provides guidance on the application of PGPR to achieve the high quality and yield of P. Praeruptorum.

Iron (Fe) bioavailability to plants is reduced in saline soils; however, the exact mechanisms underlying this effect are not yet completely understood. Siderophore-expressing rhizobacteria may represent a promising alternative to chemical fertilizers by simultaneously tackling salt-stress effects and Fe limitation in saline soils. In addition to draught, plants growing in arid soils face two other major challenges: high salinity and Fe deficiency. Salinity attenuates growth, affects plant physiology, and causes nutrient imbalance, which is, in fact, one of the major consequences of saline stress. Iron is a micronutrient essential for plant development, and it is required by several metalloenzymes involved in photosynthesis and respiration. Iron deficiency is associated with chlorosis and low crop productivity. The role of microbial siderophores in Fe supply to plants and the effect of plant growth-promoting rhizobacteria (PGPR) on the mitigation of saline stress in crop culture are well documented. However, the dual effect of siderophore-producing PGPR, both on salt stress and Fe limitation, is still poorly explored. This review provides a critical overview of the combined effects of Fe limitation and soil salinization as challenges to modern agriculture and intends to summarize some indirect evidence that argues in favour of siderophore-producing PGPR as biofertilization agents in salinized soils. Recent developments and future perspectives on the use of PGPR are discussed as clues to sustainable agricultural practices in the context of present and future climate change scenarios.

The aim of this study was to evaluate the effect of the plant growth-promoting rhizobacterium, Azospirillum brasilense, on the hydroponic cultivation of basil (Ocimum basilicum L.). The trial was carried out in the Agricultural Microbiology laboratory of the Faculty of Agricultural Sciences of the National University of Catamarca located in the city of San Fernando del Valle de Catamarca (Argentina) and basil plants were grown in the hydroponic system of "Floating Root" where 3 treatments were established (T. 1: Inoculated with Azospirillum brasilense and commercial solution for hydroponics; T. 2: Control (commercial solution for hydroponics) and T. 3 = HAKAFOS (Commercial fertilizer solution). Plant height, root length and fresh weight of the aerial part at the time of harvest were recorded. The design was completely randomized with 3 replications; the data were subjected to analysis of variance and LSD test (p≤0.05). The plants inoculated with the bacterium Azospirillum brasilense (Pi 8 strain) produced plants with greater growth than the controls and with the use of commercial fertilizer. Implementing a hydroponic system for the production of basil using the bacterial inoculant of Azospirillum brasilense (Pi 8 strain) in the nutrient solution is very efficient and achieves rapid plant growth and produces a safe food.

This study evaluated the effects of Plant Growth-Promoting Rhizobacteria (PGPR) types and concentrations on the growth and yield of soybean (Glycine max L. Merrill). The experiment was conducted from December 2023 to February 2024 in Krapyak Village, Jepara Regency, Indonesia, at an altitude of approximately 20 m above sea level on latosol soil. The study employed a factorial Completely Randomized Block Design (CRBD) with two factors: PGPR type (without PGPR, bamboo root PGPR, and commercial PGPR) and PGPR concentration (0, 10, 20, and 30 ml L⁻¹), with three replications. Observed parameters included vegetative growth traits (plant height, number of branches, flowering time), yield components (total pods per plant, empty pods, 100-seed dry weight, seed dry weight per plot), and biomass accumulation (plant fresh and dry weight). The results showed that PGPR type significantly affected the number of branches at 4 weeks after planting (WAP), total pod number, and plant fresh and dry weight. Commercial PGPR produced the highest number of branches, total pods, and biomass accumulation. PGPR concentration of 20 ml L⁻¹ resulted in the highest number of branches at 4 WAP. Significant interactions between PGPR type and concentration were observed for plant fresh and dry weight. However, PGPR application had no significant effect on plant height, flowering time, 100-seed dry weight, or seed dry weight per plot. Overall, the results indicate that PGPR effectiveness depends on microbial source and optimal concentration, with commercial PGPR showing greater potential to enhance soybean vegetative growth and pod formation under field conditions.

Plant growth promoting rhizobacteria (PGPR) have been shown to reduce abiotic stress on plants, but these effects have not been quantitatively synthesized. We evaluated the degree to which plant growth promoting rhizobacteria (PGPR) improve plant performance with and without drought stress. We used meta-analysis to summarize 52 published articles on the effects of PGPR on root mass, shoot mass and yield under well-watered and drought conditions. We also asked whether fertilization treatments, experimental conditions, inoculum taxonomic complexity, plant functional group, or inoculum delivery method introduce variation in the effect size of PGPR. Across all treatments, plants were highly responsive to PGPR; under well-watered conditions, root mass increased by 35%, shoot mass increased by 28%, and reproductive yield increased by 19%. Under drought conditions, the effect was even higher: root mass increased by 43%, shoot mass increased by 45%, and reproductive yield increased by 40%. The effect of PGPR was significantly larger under drought for shoot mass (p < 0.05) and reproductive yield (p < 0.05), but not for root mass. PGPR responsiveness also varied according to plant functional group, with C3 grass shoot production responding the least strongly to PGPR. We demonstrate that PGPR are highly effective for improving plant growth, with a greater effect under drought for above ground traits. While previously known for their bio-control abilities, we show that PGPR may also contribute to drought amelioration and water conservation.

El-Allaoui N., A. Douira, A. Benbouazza, M. Ferrahi, E. Achbani and K. Habbadi. 2024. Effect of Plant GrowthPromoting Rhizobacteria (PGPRs) on Tuber Storage of Two Potato Varieties. Arab Journal of Plant Protection, 42(2): 229-233. https://doi.org/10.22268/AJPP-001242 The potato (Solanaceae family) is a cultivated plant primarily valued for its tubers, which serve as a crucial food source for numerous populations worldwide. Losses due to postharvest diseases are significantly high and need to be reduced. To preserve tuber quality without relying on chemical treatments, the application of plant growth promoting rhizobacteria (PGPR) has been employed as a means to extend the shelf life of potato tubers. The objective of this study was to assess the effect of eight PGPRs on the conservation of two potato varieties Siena and Bellini. This was carried out in two trials; in the first trial, thirty potatoes of the Siena variety were treated with PGPRs and covered with wheat straw, and in the second trial, 160 potatoes each of the two varieties Siena and Bellini were treated with PGPRs but covered with wheat straw and black plastic. Results obtained indicated that several PGPR strains performed favorably, the most promising of which was the Aureobasidium pullulans (Ach1.1) strain that kept 50% of the treated potatoes healthy for one month in the first trial, and 30% for six months in the second trial, as compared to the negative control where 100% of the potatoes showed signs of rot in both trials. It can be concluded from this study that the Ach1.1 strain of Aureobasidium pullulans could be a promising post-harvest bio-control treatment. Keywords: PGPRs, conservation, post-harvest, potato, rot

The cultivation of perennial aromatic grasses on marginal lands is a socio‐economically and ecologically sustainable approach. However, the studies on assessment of the potential efficacies of consortium of plant growth promoting rhizobacteria (PGPR) in enhancing the productivity of perennial aromatic grasses on marginal lands are rare. In this study, therefore, we studied the effect of PGPR consortium (Pseudomonas protegens and two strains of Bacillus paramycoides) on yield and economics of four perennial aromatic grasses (Vetiveria zizanioides, Cymbopogon citratus, C. martinii, and C. winterianus) in slightly alkaline (pH &gt;8.50) soil. A field experiment was established in a complete randomized block design with two treatments (i.e. with PGPR consortium and without PGPR consortium) and three replications. The changes in growth (height, number of slips, and leaf area index), productivity (fresh shoot‐root biomass and oil yield), quality (important secondary metabolites), and economics (cost of cultivation, gross, and net return) in response to PGPR were observed at three harvests. The species‐specific effects of PGPR were found on the growth and productivity of perennial aromatic grasses. On an average, the highest increase in growth and productivity with the effect of PGPR was found in V. zizanioides followed by other grasses. The highest oil yield 16.38, 71.14, 53.13, and 49.49 kg ha−1 were recorded at third harvest in PGPR consortium treated plots for V. zizanioides, C. citratus, C. martinii, and C. winterianus, respectively. The agronomical economics show the highest net return of 2094.95 $US in the cultivation of V. zizanioides with the application of PGPR.

ABSTRACTThe present attempt was made to study the role of exogenously applied salicylic acid (SA) and putrescine (Put) on the phytoremediation of heavy metals and on the growth parameters of chickpea grown in sandy soil. The SA and Put were applied alone as well as in combination with plant growth promoting rhizobacteria (PGPR). The PGPRs, isolated from the rhizosphere of chickpea, were characterized on the basis of colony morphology and biochemical traits through gram staining, catalase and oxidase tests, and identified by 16S-rRNA gene sequencing as Bacillus subtilis, Bacillus thuringiensis and Bacillus megaterium. The chickpea seeds were soaked in 24 h old fresh cultures of isolates for 2–3 h prior to sowing. The growth regulators (PGRs), SA and Put (150 mg/L), were applied to the seedlings as foliar spray at three-leaf stage. The result revealed that plants treated with SA and Put alone or in combination with PGPRs, significantly enhanced the accumulation of heavy metals in plant shoot. PGPR induces Ni accumulation in sensitive variety and Pb in both the varieties, the PGR in combination augment the bioremediation effects of PGPR and both sensitive and tolerant variety showed significant accumulation of Ni, Cd, and Pb. SA was more effective in accumulating Ni and Cd whereas, significant accumulation of Pb was recorded in Put. PGPRs further augmented the PGRs induced accumulation of heavy metals and macronutrients in chickpea shoot and in rhizosphere. SA increased the proline content of tolerant variety while decreasing the lipid peroxidation and proline content of the sensitive variety but decreased the stimulating effect of PGPR in proline production. Interactive effects of PGPR and PGRs are recommended for inducing phytoremediation in chickpea plants under drought stress.

The effects of plant growth-promoting rhizobacteria (PGPRs) vary with their mode of inoculation, location, and dose of inorganic fertilizers applied. Therefore, it is imperative to identify the proper PGPR along with its mode of inoculation for each soil–plant system. Here, six combinations of PGPRs applied through root dip of onion seedlings were used with both 75% NPK and 100% NPK. Their performance was compared with a biofertilizer commercialized by Punjab Agricultural University as soil application (T9), two biofertilizers from Indian Agricultural Research Institute used as root dip of seedlings (T7 and T8), and two uninoculated controls [100% NPK (T0) and 75% NPK (T16)] at three locations of Punjab, India. Since interaction (PGPR × location) effects were significant, only one out of six PGPR treatments, viz. T6 (100% NPK + Azotobacter + Sphingobacterium + Burkholderia), performed consistently well across locations and gave maximum 20-bulb weight, bulb yield, net returns, and benefit:cost ratio. This treatment (T6) yielded at par with T7 and T8 but was superior to T9, which in turn yielded at par with T0 and T16 at all locations. Colonization of onion roots by beneficial natural resident arbuscular mycorrhizal fungi was higher in T6 than in control and penetration was higher when PGPRs were integrated with 75% NPK than with 100% NPK. Utilization of PGPRs with 100% NPK in light textured soils having low fertility along with poor water holding capacity and with 75% NPK in heavy textured soils having high fertility coupled with high moisture holding capacity is advocated.

This study aimed to evaluate the effects of plant growth-promoting Rhizobacteria (PGPR) treatments, B1, Azosprillium lipoferum Sp2 and B2, A. lipoferum Sp2 + Pseudomonas sp. SARS12, as well as inorganic nitrogen doses (60, 100, 140 and 180 kg N ha–1) on some soil physical characters, physiological, anatomical and yield parameters as well as nitrogen use efficiency (NUE) of wheat under water deficit stress. Results showed that water stress significantly decreased physiological characters such as chlorophyll content (6.7 and 9.8%) and relative water content (13.7 and 11.2%) in both seasons, respectively. Nevertheless, proline and malondialdehyde (MDA) were increased significantly (26.9, 12.3% and 90.2, 96.4%) in both seasons, respectively, as signals for water stress. The anatomical characteristics of flag leaves were negatively affected. Inoculation of wheat grains with PGPR significantly increased field capacity and RWC, adjusted enzymes’ activity and thus improved the physiological and yield traits and NUE as well as improving the anatomical features of flag leaves. Moreover, the combination of integrated PGPR and 140 kg N ha−1 significantly improved grain yield and its components as well as grain N uptake in comparison to control treatments. In conclusion, PGPR improved wheat productivity and NUE; they are an eco-friendly and cost-effective approach for improving plant production, and reducing nutrient leaching hazards and the negative impact of water stress.

Dual effects of plant growth-promoting rhizobacteria (PGPR) on the Moso bamboo-soil system: Plant growth promotion and microbial community stability

This research study was designed to determine the effects of plant growth-promoting rhizobacteria (PGPR) on some morphological characteristics, yield and quality contents of Hungarian vetch (Vicia pannonica Crantz.) in the Kelkit Aydin Dogan Vocational Training School Research Area during 2008-2009 and 2009-2010 plant growing season. The research consisted of a control (without plant growth-promoting rhizobacteria) and 12 different plant growth-promoting rhizobacteria (Pseudomonas putida PPB310, Bacillus cereus BCB51, Pantoea agglomerans PAB58, Pseudomonas fluorescens PFC82, Pseudomonas fluorescens PF84, Arthrobacter mysorens AM235, Paenibacillus polymyxa PP315, Pantoea agglomerans PAA362, Bacillus atrophaeus BA361, Bacillus megaterium BMA424, Bacillus megaterium BMA479 and Bacillus subtilis BS521) seed inoculations and three replicates. Some morphological characteristics (stem diameter, plant height and leaf number), dry matter yield, crude protein, crude protein yield, ADF, NDF, macro and micro-elements (B, Ca, Na, K, Mg, P, S, Cu, Fe, Mn and Zn) were tested in the research study. According to the results of the research study, some of the PGPR treatments had positive effect on morphological characteristics (especially PFC82, BA361 and PAB58), dry matter yield (very little PAA362), crude protein (very little PFC82), ADF and NDF (especially BA361) and macro and micro-elements (especially PAA362) of Hungarian vetch.

A field experiment was conducted in a wet season (Kharif) to study the effects of plant growth-promoting rhizobacteria(PGPR) inoculation on agronomic traits and productivity of Basmati rice (cv. ‘Pusa Basmati 1401’) in a randomized block with twelve treatments. We evaluated one bacterial (Providencia sp. PW5) and one cyanobacterial strain (Anabaena sp. CR3), and also a Multani mitti (Fuller’s earth)-based blue-green algal biofertilizer (a composite culture of Anabaena, Nostoc, Tolypothrix and Aulosira sp.). Plant growth, yield attributes, yield and net return of rice were significantly improved due to the rhizobacterial inoculation. The highest responses were recorded from combined inocula of bacteria and cyanobacteria together with compost.Keywords: Bacterial inoculants; BGA; cyanobacterial inoculants, PGPR; yield attributes.