Presence Of Plant Growth-promoting Rhizobacteria Research Articles

Soil microorganisms buffer the reduction in plant growth and physiological performance under combined abiotic stress in the halophyte Salicornia ramosissima

The impact of multifactorial abiotic stress combinations on plant functional responses remains controversial, and general patterns of response are yet to emerge. This knowledge gap is particularly relevant for species with innate tolerance to environmental stress. Using the halophyte Salicornia ramosissima as a model species, we performed a multifactorial study with 16 experimental scenarios that included or not beneficial microorganisms in order to quantify their impact on plant growth, photosynthetic performance, osmotic adjustment and ion homeostasis. The experimental scenarios were characterized by the combination of four factors with two levels (salinity: 171 and 510 mM NaCl; water stress: yes and no; temperature min/max range: 14/25 and 18/29ºC and atmospheric CO2 concentration: 400 and 700 ppm). A plant growth-promoting rhizobacteria (PGPR) consortium was used as a proxy for positive biological interaction. The results revealed that the multifactorial stress combinations triggered unique functional responses, depending on the stress factors involved. However, there was an overall more negative impact on plant functional traits under the most extreme scenario (i.e., 510 mM NaCl + water stress + high temperature). Interestingly, the presence of PGPR was able to reverse this negative influence, although this effect was negligible under non-stressful conditions. Furthermore, the positive effect of PGPR was even magnified when coexisting with elevated atmospheric CO2 concentration. This response is associated with mitigation of the negative impacts of suboptimal factor combinations on plant growth, photosynthetic performance/efficiency, and water/nutrient homeostasis. Therefore, we conclude that the positive impact of microorganisms on halophyte tolerance in complex environmental matrices would only be determinant under extreme conditions in which plant intrinsic tolerance mechanisms would not be sufficient. Remarkably, this effect could be accentuated by increasing atmospheric CO2 concentration.

Diversity of Rhizo-Bacteriome of Crocus sativus Grown at Various Geographical Locations and Cataloging of Putative PGPRs

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.

Potential of plant growth promoting Rhizobacteria to overcome the exposure of pesticide in Trigonella foenum - graecum (fenugreek leaves)

Abstract Agrochemicals are generally used as additional supplements to the soil for improving soil fertility throughout the world. In this present study was carried out to characterize the pesticide tolerance plant growth promoting rhizobacteria (PGPR) were isolated from fenugreek leaves. Seven bacterial isolates were obtained namely FOW1 to FOW7 and characterized on their colony morphology, size and colour. Among the seven, FOW1 and FOW7 isolates were found to grown well in nutrient medium containing 10–20% concentration of pesticide. All the seven isolates were produced indole-3- acetic acid in the range of 56–97 μg/mL and only two isolates (FOW1 and FOW7) displayed the phosphate solubilising activity in Pikovskaya agar, whereas six isolates were showed positive for production of siderophore. Out of seven isolates, two exhibited in vitro plant growth promotion activities and indicated that these isolates can be exploited as biofertilizers and microbial inoculants for crops as they enhanced plant growth via diverse mechanisms and offered an attractive strategy to replace synthetic fertilizers and pesticides. The morphological features such as germinating ability, shoot length, root length were enhanced in the presence of PGPR and was maximum at 1%.

Evidence of a trade-off between root aeration and architecture in Vallisneria natans in the presence of Pseudomonas putida KT2440

In this work, we investigated the relationship between root plasticity and root oxygen dynamics in the presence of plant growth-promoting rhizobacteria (PGPR). A gnotobiotic system was used to study how the root architecture, radial O2-loss patterns, and internal O2 transport of the eelgrass Vallisneria natans (Hydrocharitaceae) changed in response to inoculation with a common soil PGPR, Pseudomonas putida (KT2440). Our results showed no radial O2-loss barrier in the roots of V. natans, meaning that the entire root surface exhibited the same capacity for O2 release. However, this morphological trait stimulated external oxygen demand in KT2440, thus reducing internal root O2 transport. Moreover, the distribution of root hairs (RHs), which was modified by exposure to KT2440, also significantly impacted internal O2 transport. The altered RH distribution minimized oxygen loss on the upper half of the root, and dense adventitious roots with overlapping rhizospheres enabled a highly oxygenated zone around the root base. Thus, these changes protect roots against low oxygen conditions. Furthermore, the presence of many RHs on the roots’ lower halves can increase nutrient absorption from anoxic sediments. In conclusion, this study demonstrates a complex trade-off between root aeration and architecture in V. natans that may help this plant adapt to submerged conditions when KT2440 is present.

Neighbor Presence of Plant Growth-promoting Rhizobacteria (PGPR) and Arbuscular Mycorrhizal Fungi (AMF) Can Increase Sorghum Phytoremediation Efficiency in a Soil Treated with Pb Polluted Cow Manure

Neighbor Presence of Plant Growth-promoting Rhizobacteria (PGPR) and Arbuscular Mycorrhizal Fungi (AMF) Can Increase Sorghum Phytoremediation Efficiency in a Soil Treated with Pb Polluted Cow Manure

Bioavailability of Zn from layered double hydroxides: The effects of plant growth-promoting rhizobacteria (PGPR)

There is widespread interest in developing layered double hydroxides (LDH) in agricultural applications to supply essential nutrients for plants. The present study sought to gain a better understanding of the specific effects of Zn-Mg-Fe(III)-LDH intercalated with nitrate (LDH-N) and phosphate (LDH-P) anions in the absence and presence of plant growth-promoting rhizobacteria (PGPR) on Zn phyto-availability, using sand culture experiments. The LDH were synthesized and their characteristics were investigated by XRD patterns, FT-IR spectra, and elemental analysis. In the first experiment, predetermined amounts of LDH-N or LDH-P mixed with 500 g sand quartz to provide 0, 5, 15, 25 and 50 mg Zn kg−1 sand. In the second study, the potential of three pseudomonas strains, i.e., pseudomonas sp. A5 (P1), p. putida P19 (P2) and P. fluorescens P52 (P3) (high Zn-solubilizing bacteria) on kinetic release and plant availability of Zn from LDH were investigated in a batch and a pot experiment. The LDH appreciably improved the Zn content of plants, irrespective of the sources applied. However, the concentration and uptake of Zn in root and shoot of maize plants grown in the LDH-N-sand system were higher than those grown in the LDH-P-sand culture. Results of the second experiment showed that, in the LDH-N treatments, all the three pseudomonas strains increased Zn content of roots and shoots. While in the LDH-P treatments, none of the strains had a significant effect on Zn concentrations of root and shoot as compared to the control. According to the results of the batch study, the ability of bacteria in cumulative Zn released increased by increasing the time of incubation. Among three strains, the highest cumulative Zn release from LDH was recorded in the presence of P2, followed by P1 and P3 strains. This study suggested that LDH-N and LDH-P are effective sources for the supply of Zn and improving the growth of maize under Zn deficiency conditions and also highlighted the potential of PGPR to increase Zn availability.

Plant growth promoting rhizobacteria increase the efficiency of fertilisers while reducing nitrogen loss

More than half of the applied conventional fertiliser nitrogen (N) in cropping systems can be lost to the environment, resulting in water and air pollution. Farming systems that ensure efficient fertiliser use are crucial to sustain crop productivity without harming the environment. One avenue to achieve this is the use of bio-fertilisers with recognised benefits for plant nutrition and soil heath. Within this area, plant growth promoting rhizobacteria (PGPR) are increasingly applied to enhance plant nutrient acquisition and assimilation. Here, we investigated if PGPR can improve fertiliser performance. We show that the addition of PGPR to soils amended with 50% organic and 50% conventional N fertilisers increased the growth of kikuyu grass (Pennisetum clandestinum), producing yields similar to those obtained using 100% conventional N fertiliser. Encouragingly, this combination also reduced mineral N leaching by 95% relative to the all conventional fertiliser treatment. These findings suggest that using organic and synthetic fertilisers together in the presence of PGPR is a promising approach for sustaining plant growth while reducing potential pollution from inefficient use of conventional N fertilisers.

Mycorrhizal colonization and phosphorus uptake in presence of PGPRs along with nematode infection

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.

Drought response of Mucuna pruriens (L.) DC. inoculated with ACC deaminase and IAA producing rhizobacteria.

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.

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

Introducing specific microorganisms into the soil ecological system is an important strategy for improving nutrient use efficiency. Two pot experiments were conducted in the greenhouse from December 3, 2012 to January 25, 2013 (Experiment 1) and March 11 to April 23, 2013 (Experiment 2) to evaluate the effect of nitrogen (N) source and inoculation with plant growth-promoting rhizobacteria (PGPR) on plant growth and N and phosphorus (P) uptake in tomato (Lycopersicon esculentum Mill.) grown on calcareous soils from South Florida, USA. Treatments included urea, controlled release urea (a controlled release fertilizer, CRF) each at low and high N rates and with or without inoculation of PGPR. A mixture of PGPR strains Bacillus amyloliquefaciens IN937a and Bacillus pumilus T4 was applied to the soil during growing periods of tomato. Treatments with PGPR inoculation increased plant height compared to treatments without PGPR in both experiments. Inoculation with PGPR increased shoot dry weight and shoot N uptake for the same N rate and N source. In both experiments, only at high N rate, CRF and urea treatments with PGPR had significantly (P < 0.05) greater shoot biomass than those without PGPR. Only at high N rate, CRF treatment with PGPR significantly increased shoot N uptake by 39.0% and 10.3% compared to that without PGPR in Experiments 1 and 2, respectively. Meanwhile, presence of PGPR in the soil increased shoot P uptake for all treatments in Experiment 1 and for most treatments in Experiment 2. In Experiment 1, only at low N rate, CRF treatment with PGPR significantly increased shoot P uptake compared with that without PGPR. In Experiment 2, a significant increase in shoot P uptake by inoculation of PGPR was only observed in CRF treatment at high N rate. Results from this study indicate that inoculation with PGPR may increase plant growth and N and P uptake by tomato grown on calcareous soils. However, the effect of PGPR varied and was influenced by many factors such as N source, N rate, and soil fertility. Further investigations are warranted to confirm the effect of PGPR under different soil conditions.

Modulation of phytoremediation and plant growth by the treatment with PGPR, Ag nanoparticle and untreated municipal wastewater

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.

Alleviation of Mercury Toxicity in Wheat by the Interaction of Mercury-Tolerant Plant Growth-Promoting Rhizobacteria

Heavy metal contamination of agricultural soils has increased along with industrialization. Mercury is a toxic heavy metal and a widespread pollutant in the ecosystem. Mercury-tolerant and plant growth-promoting rhizobacteria (PGPR) HG 1, HG 2, and HG 3 were isolated from the rhizosphere of plants growing in a mercury-contaminated site. These isolates were able to grow in the presence of mercury ranging from 10 to 200 µM in minimal medium and 25 to 500 µM in LB medium. The strains were characterized by morphological, biochemical, and plant growth-promoting traits. In the present study, these PGPR strains were analyzed for their involvement in metal stress tolerance in Triticum aestivum (wheat). Two bacterial strains, namely, Enterobacter ludwigii (HG 2) and Klebsiella pneumoniae (HG 3), showed better growth promotion of T. aestivum seedlings under metal stress. Different growth parameters like, water content and biochemical properties were analyzed in the PGPR-inoculated wheat plants under 75 µM HgCl2. Shoot length, root length, shoot dry weight, root dry weight and relative water content (RWC) were significantly higher in inoculated plants compared to uninoculated plants under stress condition. Proline content, electrolyte leakage, and malondialdehyde content (shoots and roots) were significantly lower in inoculated plants with respect to uninoculated plants under mercury stress. Therefore, it could be assumed that all these parameters collectively improve plant growth under mercury stress conditions in the presence of PGPR. Hence, these PGPRs can serve as promising candidates for increasing plant growth and also have immense potential for bioremediation of mercury-contaminated soils.

Beneficial Microbes Affect Endogenous Mechanisms Controlling Root Development.

Plants have incredible developmental plasticity, enabling them to respond to a wide range of environmental conditions. Among these conditions is the presence of plant growth-promoting rhizobacteria (PGPR) in the soil. Recent studies show that PGPR affect Arabidopsis thaliana root growth and development by modulating cell division and differentiation in the primary root and influencing lateral root development. These effects lead to dramatic changes in root system architecture that significantly impact aboveground plant growth. Thus, PGPR may promote shoot growth via their effect on root developmental programs. This review focuses on contextualizing root developmental changes elicited by PGPR in light of our understanding of plant-microbe interactions and root developmental biology.

Soil bacteria hold the key to root cluster formation.

Root clusters are bunches of hairy rootlets that enhance nutrient uptake among many plants. Since first being reported in 1974, the involvement of rhizobacteria in their formation has received conflicting support. Attempts to identify specific causative organisms have failed and their role has remained speculative. We set up a gnotobiotic experiment using two root-clustered species, Viminaria juncea (Fabaceae) and Hakea laurina (Proteaceae), and inoculated them with two plant-growth-promoting rhizobacteria (PGPR), Bradyrhizobium elkanii and Bacillus mageratium, that produce indole-3-acetic-acid (IAA). Plants were suspended in water culture with four combinations of nitrogen and phosphorus. Clusters only developed in the presence of PGPR in two treatments, were greatly enhanced in another four, suppressed in five, and unaffected in five. Nitrogen amendment was associated with a higher density of clusters. Bradyrhizobium promoted cluster formation in Hakea, whereas Bacillus promoted cluster formation in Viminaria and suppressed it in Hakea. Greater root cluster numbers were due either to a larger root system induced by PGPR (indirect resource effect) and/or to more clusters per unit length of parent root (direct morphogenetic effect). The results are interpreted in terms of greater IAA production by Bradyrhizobium than Bacillus and greater sensitivity of Viminaria to IAA than Hakea.

COMPLEMENTED EFFECT OF GLYCINE BETAINEA AND BIOFERTILIZERS ON GROWTH AND PRODUTIVITY OF SWEET PEPPER (Capsicum annuum L.) PLANT UNDER HIGH TEMPERATURE CONDITION.

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.

Improved Salinity Tolerance of Arachis hypogaea (L.) by the Interaction of Halotolerant Plant-Growth-Promoting Rhizobacteria

Salinity adversely affects plant growth and development. Halotolerant plant-growth-promoting rhizobacteria (PGPR) alleviate salt stress and help plants to maintain better growth. In the present study, six PGPR strains were analyzed for their involvement in salt-stress tolerance in Arachis hypogaea. Different growth parameters, electrolyte leakage, water content, biochemical properties, and ion content were analyzed in the PGPR-inoculated plants under 100 mM NaCl. Three bacterial strains, namely, Brachybacteriumsaurashtrense (JG-06), Brevibacteriumcasei (JG-08), and Haererohalobacter (JG-11), showed the best growth of A. hypogaea seedlings under salt stress. Plant length, shoot length, root length, shoot dry weight, root dry weight, and total biomass were significantly higher in inoculated plants compared to uninoculated plants. The PGPR-inoculated plants were quite healthy and hydrated, whereas the uninoculated plant leaves were desiccated in the presence of 100 mM NaCl. The percentage water content (PWC) in the shoots and roots was also significantly higher in inoculated plants compared to uninoculated plants. Proline content and soluble sugars were significantly low, whereas amino acids were higher than in uninoculated plants. The MDA content was higher in uninoculated plants than in inoculated plants at 100 mM NaCl. The inoculated plants also had a higher K+/Na+ ratio and higher Ca2+, phosphorus, and nitrogen content. The auxin concentration was higher in both shoot and root explants in the inoculated plants. Therefore, it could be predicted that all these parameters cumulatively improve plant growth under saline conditions in the presence of PGPR. This study shows that PGPR play an important role in inducing salinity tolerance in plants and can be used to grow salt-sensitive crops in saline areas.

Effect of the combined inoculation of arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria on papaya (Carica papayaL.) infected with the root-knot nematodeMeloidogyne incognita

Introduction . Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) can be considered important rhizospheric beneficial microorganisms. Their use as biocontrol strategies against soilborne pathogens such as nematodes should be taken into account. However, optimal management of soil microbiota communities is not easy because of the high specificity involved in these types of interactions. The aim of our study was to determine whether the combined inoculation of two AMF species and a Bacillus consortium based on three strains previously described as PGPR in other crops were able to reduce nematode infection and damage on papaya. Materials and methods . Papaya seedlings were inoculated with two AMF isolates (Glomus mosseae or G. manihotis ) at the beginning of the nursery phase. Once the mycorrhizal symbiosis was established, a Bacillus consortium was applied. Nematode inoculum was applied 20 d after transplanting to individual pots. Plants were harvested 160 d after nematode inoculation. Results . In terms of plant development and nutrition, benefits due to AMF inoculation persisted in the presence of PGPR. However, the effect of dual inoculation was different, depending on the Glomus species. This positive effect was also evident in plants with nematode. Meloidogyne infection was significantly reduced in mycorrhizal plants. However, the addition of PGPR does not seem to improve the results of AMF single treatments in terms of nematode infection. Conclusion . Dual application of AMF and PGPR must be considered for papaya threatened by the root-knot nematode, although a previous screening should be done in order to select the best microbe combination to optimise results.