Root-knot nematodes (RKN) cause extensive damage to grapevine cultivars. RKN-resistant grapevine rootstocks remain vulnerable to biotic and abiotic stresses. This study aimed to determine the influence of composted animal manures (CAMs) [chicken manure (CM), cow manure (CowM), and sheep manure (SM)] with or without plant growth-promoting rhizobacteria (PGPR) on the population of Meloidogyne incognita, free-living nematodes (FLNs) and predaceous nematodes (PNs) residing in the soils of vineyard cultivars (Flame, Superior and Prime). The nematodes were isolated from grapevine roots and rhizosphere soils, then the absolute frequency of occurrence (FO), relative FO, prominence value (PV), and population density (PD) were assessed. The impact of CAMs and PGPR on the growth parameters, fruit output, and quality of three grapevine varieties was subsequently evaluated. Eight treatments included a control without CAMs or PGPR amendments, the CAMs alone, or CAM treatments combined with PGPR. The results showed that FLNs and PNs were more abundant in Prime than Flame or Superior cultivars when poor sandy loam soils were supplied with CAMs. Among all tested manures, CM was the best treatment as a nematicide. This was evident from the decreased numbers of M. incognita and increased numbers of FLNs and PNs in grapevine fields. Compared to the soil-applied oxamyl (a systemic nematicide), which was efficiently suppressive on M. incognita for two months, CM significantly (P < 0.05) decreased PD of the phytonematodes for five months, improved soil structure and enhanced the soil biological activities. There were significant (P < 0.05) increases in the number of leaves/vines by 79.9, 78.8, and 73.1%; and total fruit weight/vine by 76.9, 75.0, and 73.0% in Flame, Superior, and Prime varieties, respectively, compared to untreated vines. Regardless of the cultivar, soils amended with CM + PGPR achieved the lowest number of M. incognita among all other treatments, followed by SM + PGPR and CowM + PGPR. It was concluded that CAMs amendment, mainly CM, along with PGPR in poor sandy soils of temperate areas, is considered a sustainable approach for reducing parasitic nematodes and improving agricultural management.
Soil salinization has been the major form of soil degradation under the dual influence of climate change and high-intensity human activities, threatening global agricultural sustainability and food security. High salt concentrations induce osmotic imbalance, ion stress, oxidative damage, and other hazards to plants, resulting in retarded growth, reduced biomass, and even total crop failure. Halo-tolerant plant growth promoting rhizobacteria (HT-PGPR), as a widely distributed group of beneficial soil microorganisms, are emerging as a valuable biological tool for mitigating the toxic effects of high salt concentrations and improve plant growth while remediating degraded saline soil. Here, the current status, harm, and treatment measures of global soil salinization are summarized. The mechanism of salt tolerance and growth promotion induced by HT-PGPR are reviewed. We highlight that advances in multiomics technologies are helpful for exploring the genetic and molecular mechanisms of microbiota centered on HT-PGPR to address the issue of plant losses in saline soil. Future research is urgently needed to comprehensively and robustly determine the interaction mechanism between the root microbiome centered on HT-PGPR and salt-stressed plants via advanced means to maximize the efficacy of HT-PGPR as a microbial agent. Halo-tolerant plant growth promoting rhizobacteria (HT-PGPR) are a valuable biological tool for mitigating the toxic effects of high salt concentrations. And the microbiome centered on HT-PGPR is solutions for sustainable agriculture in saline soils.
Introduction Botrytis cinerea is one of the pathogenic fungi causing major problems worldwide in crops such as tomato. Some Plant Growth-Promoting Rhizobacteria (PGPR) can activate induced systemic resistance (ISR) pathways in crops, reducing the need for antifungals.Methods Three strains belonging to the species Peribacillus frigoritolerans (CD_FICOS_02), Pseudomonas canadensis (CD_FICOS_03), and Azotobacter chroococcum (CD_FICOS_04), which exhibit outstanding PGPR properties, were evaluated for their ability to protect tomato plants against B. cinerea infection by ISR via soil inoculation.Results The strains CD_FICOS_02 and CD_FICOS_03 reduced B. cinerea incidence and plant oxidative stress. The first strain mainly increased the expression of genes related to the salicylic acid pathway, while the second increased the expression of genes related to the jasmonic acid/ethylene hormonal pathway, indicating preferential ISR activation by each of these pathways. In addition, CD_FICOS_03 was able to increase the root and aerial biomass production of infected plants compared to the control. Interestingly, although the strain CD_FICOS_04 did not reduce the damage caused by B. cinerea, it increased the biomass of infected plants.Discussion Our results suggest that the best strategy for biocontrol of B. cinerea is to combine the ability to promote plant growth with the ability to induce systemic resistance, as demonstrated by strains P. frigoritolerans CD_FICOS_02 and P. canadensis CD_FICOS_03.
Tylenchulus semipenetrans is a soil-borne pathogen that causes substantial damage and economic losses to citrus crops worldwide. Due to the high toxicity of chemical nematicides to humans and the environment, biocontrol bacteria have emerged as a promising alternative for managing citrus nematodes. This study aimed to screen bacterial strains for their efficacy to control T. semipenetrans and assess their impact on citrus plant growth. A total of 107 bacterial strains were isolated from the soil and roots of infested citrus trees. Among these, five strains exhibited significant nematicidal activity against T. semipenetrans. Four bacterial densities were tested for each strain: 3.6 x 10(5), 2.5 x 10(4), 3.6 x 10(3), and 1.2 x 10(3) cells/ml. These strains were tested both individually and in combination to evaluate their efficacy. The five strains were identified as Variovorax paradoxus, Bacillus pseudomycoides, Bacillus simplex, Bacillus cereus, and Paracoccus speluncae based on physiological, biochemical, and molecular (16S rRNA gene sequences) analyses. Juvenile mortality (J2s) and egg hatching inhibition were positively correlated with bacterial concentration and exposure duration. The highest juvenile mortality (100%) was observed with a combination of all five bacteria (3.6 x 10(5) cells/ml) after 96 h, while B. cereus alone achieved 98.98% mortality. The maximum nematicidal activities of the bacterial filtrates were generally observed between the 4th and 6th days of incubation, coinciding with peak bacterial growth and biomass production. The selected isolates also demonstrated the ability to produce indole acetic acid and solubilize phosphorus. In greenhouse experiments, the five isolates reduced T. semipenetrans populations by up to 62.96% compared to the control. Additionally, all rhizosphere bacteria and their combination significantly enhanced plant growth parameters (p < 0.0001). Notably, P. speluncae BR21 has not previously been tested for nematicidal effects on any nematode, making this the first documented report of its nematicidal potential.
The Meloidogyne spp., commonly known as root-knot nematodes (RKN), are obligate sedentary endoparasites considered among the most damaging plant-parasitic nematodes globally. They harm crops by using parasitic proteins to alter host cell physiology, which promotes parasitism and reduces crop yield. Traditional RKN management, primarily through chemical control, negatively impacts the nutritional value, soil texture, and vegetable production, and poses risks to human health and the environment. An emerging eco-friendly and costeffective alternative is the use of plant growth-promoting microbes (PGPM)-mediated biological approaches. The PGPM enhances plant growth directly by solubilizing phosphorus and iron, fixing nitrogen, producing phytohormones, siderophores, and ammonia, or indirectly through competition, antibiosis, hydrogen cyanide, 1-aminocyclopropane-1-carboxylate (ACC) deaminase enzyme, and exopolysaccharides (EPS) production. This review explores various RKN management strategies, emphasizing green biological approaches, their benefits and drawbacks, current commercial status and usage, and the underlying genes, challenges, and limitations associated with these methods.
Salt stress threatens global food security, and although plant growth-promoting rhizobacteria (PGPR) can boost plant resistance and productivity, their field effects are poorly understood. Therefore, this experimental trial explored the mechanisms of PGPR-induced salt stress resistance on ion homeostasis, the photosynthetic system, enzymatic activities, and rhizosphere diversity in rice. The study was conducted in the first week of May 2022, using rice (Tongxi 945) seeds, which were pelleted at the seedling nursery and cultivated in the field under salinity conditions (0.5 and 2.35 g kg- 1) with (+) or without (-) PGPR treatment. Na+/K+ concentrations, photosynthetic, leaf water potential, enzymatic activities, and changes in rhizosphere microorganisms were measured at the heading stage of rice. The findings of this study revealed that salinity stress significantly increased Na+ concentrations in leaves (257.70%), the leaf Na+/K+ ratio (567.96%), and leaf water potential (63.47%) while markedly reducing the net photosynthetic rate (71.72%), stomatal conductance (81.36%), thousand-grain weight (2.22%), and yield (114.15%). However, the application of PGPR mitigated the adverse effects of salinity stress by reducing Na+ concentrations in roots (45.22%) and leaves (26.20%), the root Na+/K+ ratio (64.68%), and leaf water potential (31.39%). PGPR also significantly improved the net photosynthetic rate (29.75%), stomatal conductance (46.89%), transpiration rate (25.56%), and chlorophyll content (11.95%). Applying PGPR significantly enhanced antioxidant enzyme activity, regulated carbon metabolism, increased microbial diversity in rhizosphere soil, and boosted the abundance of dominant fungal genera, alleviating salt stress damage to rice. Overall, PGPR improves microbial diversity, photosynthesis, and enzyme activities, mitigating salt stress effects. Further research is necessary to implement these findings in agriculture and evaluate their long-term impacts on crop productivity and soil health.
Salinity stress is an ever-present threat to crop productivity and its extent is continuously increasing due to climate change and anthropogenic activities. The accumulation of excessive concentration of salts disturbs photosynthesis, and hormonal balance and causes nutrient imbalance, ionic toxicity, and osmotic stress which in turn reduce the final yield and quality. Further, excessive concentrations of salts also induce reactive oxygen species (ROS) production that damages the cellular membranes, proteins, lipids, and photosynthetic apparatus and cause a reduction in the synthesis of photosynthetic pigments. Therefore, it is mandatory to develop the appropriate measures to mitigate the adverse impacts of salinity tolerance in plants. The development of salt-tolerant crops, exogenous application of hormones and osmoprotectants, nutrient application, plant growth promoting rhizobacteria (PGPR), arbuscular mycorrhizal fungi (AMF), biochar and nano-particles can help to mitigate the adverse impacts of salinity on plants. In the present review, the effects of salt stress on plants, the mechanism of salt tolerance in plants and different strategies that can be used to mitigate adverse effects of salinity are discussed. This review will provide new insights into existing knowledge to ensure better crop production in salt-affected soils.
The land areas and crop species adversely impacted by salinity and heavy metals are growing rapidly. Current research indicates that plant growth-promoting microorganisms offer an environmentally friendly option for improving physiological and biochemical processes in plants growing under stress conditions. The aim of the present study was to investigate the potential mitigation of simultaneous salinity and cadmium (Cd) stress in rapeseed ( Brassica campestris cv. BARI Sarisha-17) by the application of Azospirillum sp. (Az), phosphate solubilizing bacteria (PSB), potassium mobilizing bacteria (KMB), and vesicular arbuscular mycorrhiza (VAM). Seeds were treated with PSB or KMB prior to sowing, whereas Az, PSB, KMB, or VAM were added as supplements during soil preparation. At 21 days after sowing, the plants were treated with a combination of salt (100 mM NaCl) and Cd (0.25 mM CdCl2), with several applications at 7-day intervals. The combination of salt and Cd stress decreased plant growth and biomass, relative water content, and photosynthetic pigment levels, while also increased electrolyte leakage, lipid peroxidation, and the generation of excess reactive oxygen species (ROS). Salt and Cd stress also impaired plant ion balances of sodium, potassium and nitrate, antioxidant defenses, and glyoxalase system activity. Application of Az, PSB, or KMB restored these parameters to unstressed levels by facilitating the scavenging of ROS, maintaining water status, restoring ion balances, enhancing plant antioxidant defenses, and increasing glyoxalase enzyme activity, while reducing methylglyoxal toxicity and improving photosynthetic activity. The application of KMB was the most effective; however, all microbe supplementations showed the ability to alleviate the damage caused by stress in rapeseed. These findings highlight the ability of soil microorganisms with plant growth-promoting properties to improve the physiological and biochemical functions of rapeseed under Cd and salt stress.
Soil salinization and alkalinization are pervasive environmental issues that severely restrict plant growth and crop yield. Utilizing plant growth-promoting rhizobacteria (PGPR) is an effective strategy to enhance plant tolerance to saline-alkaline stress, though the regulatory mechanisms remain unclear. This study employed biochemical and RNA-Seq methods to uncover the critical growth-promoting effects of Trichoderma spp. on Salix linearistipularis under saline-alkaline stress. The results showed that, during saline-alkaline stress, inoculation with Trichoderma sp. M4 and M5 significantly increased the proline and soluble sugar contents in Salix linearistipularis, enhanced the activities of SOD, POD, CAT, and APX, and reduced lipid peroxidation levels, with M4 exhibiting more pronounced effects than M5. RNA-Seq analysis of revealed that 11,051 genes were upregulated after Trichoderma sp. M4 inoculation under stress conditions, with 3532 genes primarily involved in carbon metabolism, amino acid biosynthesis, and oxidative phosphorylation-processes that alleviate saline-alkaline stress. Additionally, 7519 genes were uniquely upregulated by M4 under stress, mainly enriched in secondary metabolite biosynthesis, amino acid metabolism, cyanamide metabolism, and phenylpropanoid biosynthesis. M4 mitigates saline-alkaline stress-induced damage in Salix linearistipularis seedlings by reducing oxidative damage, enhancing organic acid and amino acid metabolism, and activating phenylpropanoid biosynthesis pathways to eliminate harmful ROS. This enhances the seedlings' tolerance to saline-alkaline stress, providing a basis for studying fungi-plant interactions under such conditions.
Soil salinization, a rising issue globally, is a negative effect of the ever-changing climate, which has drawn attention to, and exacerbated problems related to soil degradation and the decline in wetland rice (Oryza sativa L.) production, leading to an unstable national economy. The use of rhizosphere inhabiting microorganisms (plant growth-promoting rhizobacteria, PGPR) is a viable method for boosting agricultural production on saline soils and reduce salt stress in rice crops. The objective of this study was to support the development of rice under salt stress by using a consortium of bacterial strains. 'Pokkali' rice plants inoculated with single Bacillus tequilensis and B. aryabhattai isolates were compared with consortium and non-inoculated plants while salinity was increased and by irrigation with tap water (control), 30 mM (5 dS m(-1)) and 60 mM (10 dS m(-1)) NaCl. The present study exhibited that inoculation of a mixed inoculum at 5 dS m(-1) resulted in significantly higher dry weight of the shoots and roots of seedlings (9.29 and 1.24 g, respectively) which was due to the increased SPAD value, proline content (7.55 mu mol g(-1) FW), and antioxidant enzyme activity in the inoculated plants. The higher accumulation of osmoprotectants such as proline supported Na+ ion reduction and antioxidant enzymes such as ascorbate peroxidase and reduced polyphenol oxidase content protect against higher cellular damage, eventually leading to increase plant growth performance in saline soil. This study demonstrates some positive effects of the locally isolated salt tolerant consortium PGPR strains on the growth of rice plants under salt stress conditions.