Rice Endophytic Bacteria Research Articles

Screening of endophytic bacteria antagonistic against Ustilaginoidea virens in rice

Rice false smut (RFS) caused by Ustilaginoidea virens is a major disease in rice-producing areas in China. Endophytic bacteria have prominent advantages in controlling host plant diseases. To screen and obtain the antagonistic bacteria of RFS and effectively control RFS, the antagonistic strains were screened from 45 rice endophytic bacteria by the method of plate pair culture, the antagonistic activity of the fermentation broth of the antagonistic strains was measured, and the RFS field control test was performed. The results showed that 45 strains of rice endophytic bacteria had antagonistic activity against on U. virens, of which 23 strains had an antagonistic band of more than 15 mm. The fermented broth of these 23 antagonistic strains had strong antagonistic activity against on U. virens, of which 17 strains had antagonistic band of more than 20 mm, and 3 of them (REB01, REB32, and REB42) had more than 28 mm. . The three strains (REB01, REB32 and REB42) had 81.48%, 72.05% and 76.76% of respectively field control effect on RFS, which was very significant (P <0.01) higher than the field control effect of 500-fold dilution of 5% Jinggangmycin (61.72%), and showing great potential for biological control of RFS.

Studies on suppression of bacterial leaf blight by rice endophytic bacteria under field condition

A total of 45 endophytic bacterial isolates were isolated from the healthy rice cultivars viz; MTU 1010, BPT 5204 and NLR 34449 cultivated in Nellore and Chittoor districts of Andhra Pradesh. All the isolated endophytic bacterial isolates were evaluated for their antagonistic effect against bacterial leaf blight (BLB) pathogen Xanthomonas oryzae pv. oryzae by agar well diffusion method. The diameter of inhibition zone formation ranged from 0 mm to 16.8 mm. Among 45 isolates, EMP-5 and EBK-3 isolates showed highest antagonistic effect with inhibition zone of 16.8 mm and 16.6 mm, respectively. Isolate EMP 5 was used for the management of BLB under field condition. Among all the treatments, treatment T5 (i.e., seed treatment with EMP-5 @ 109 cells ml-1 + foliar application of EMP-5 @109 cells ml-1) exhibited highest reduction in disease index (4.92 %), increased plant growth promoting ability with plant height of 80.8 cm, increase in the no. of effective tillers (97.4 %), grain yield (5340 kg ha-1) and straw yield (6013 kg ha-1) over the untreated control. The results strongly emphasize that endophytic bacteria (EMP-5) could be efficiently used for management of bacterial leaf blight.

Diazinon degradation by bacterial endophytes in rice plant (Oryzia sativa L.): A possible reason for reducing the efficiency of diazinon in the control of the rice stem-borer.

It is well known that microorganisms can reduce the effectiveness of organophosphate pesticides after their application. But, little information is available concerning the effect of rice endophytic bacteria on the degradation of diazinon, an organophosphate pesticide used in control of the rice stem-borer, absorbed by the rice plant. Thus, aim of this study was to characterize the endophytic bacterial isolates, isolated from diazinon-treated and non-treated rice plants in paddy fields, in terms of diazinon degradation and to investigate whether potent isolates that degrade diazinon invitro might have the same effect in the rice plant. The results showed that all endophytic isolates, isolated from both groups of rice plants (diazinon-treated and non-treated rice plants), could grow in mineral salt medium (MSM) supplemented with diazinon (20mgL-1) as a sole carbon source, and 3.79-58.52% of the initial dose of the insecticide was degraded by the isolates within 14d of incubation. Phylogenetic analysis based on 16S rRNA sequencing indicated that the potent isolates (DB26-R and B6-L) clearly belonged to the Bacillus genus. The diazinon concentrations in rice plants co-inoculated with B.altitudinis DB26-R and B.subtilis subsp. Inaquosorum B6-L and single-inoculated with these strains were reduced significantly compared with endophyte-free rice plants. These results provide unequivocal evidence that the rice endophytic bacteria, in addition to invitro degradation of diazinon, are also involved in the rapid inactivation of diazinon in rice plants treated with diazinon (invivo degradation of diazinon).

Antifungal Potency of Secondary Metabolites Produced by Endophytic Bacteria against Pathogenic Fungi Pyricularia oryzae Cav.

Blast disease caused by Pyricularia oryzae Cav. is one of the most important diseases on rice. One of the alternative controlling methods in P. oryzae is biological control through the utilization of secondary metabolites produced by endophytic bacteria. The study aimed to determine the antifungal potency of secondary metabolites produced by rice endophytic bacteria against P. oryzae. The experiment was conducted using 9 endophytic bacteria isolated rice (Os1, Os2, Os3, Os4, Os5, Os6, Os7, Os8, and Os10). Each isolates were grown in ISP2 liquid media and the secondary metabolites compounds were extracted using two different solvents; methanol and ethyl acetate : methanol (4:1) (v/v). The effect of secondary metabolites was tested using agar well diffusion method. The results demonstrated that the secondary metabolites extracted by both solvents have antifungal effect on the growth of P. oryzae. The highest growth inhibition was shown by secondary metabolites extracted by ethyl acetate : methanol (4:1) from Os1 (42%) and Os3 (39%). Antifungal activity of the secondary metabolites was indicated by the formation of clear zone. HPLC (High Performance Liquid Chromatography) analysis showed the differences of peaks and retention time between secondary metabolites produced by Os1 and Os3 which has antifungal activity and secondary metabolites produced by Os10 that did not show the antifungal activity.

Root bacterial endophytes as potential biological control agents against fungal rice pathogens

The present work was carried out to investigate the potential of 100 rice endophytic bacteria for the biocontrol of five fungal rice pathogens in a controlled environment. As well as, isolates with antagonistic activity were also characterized in terms of production of some plant growth promoting (PGP) traits. Twenty-three isolates repressed the mycelial growth of some fungal rice pathogens (70–96% inhibition). The results illustrated that production ability of PGP traits was different among biocontrol isolates. Higher % of the isolates was positive for generation of ACC deaminase, IAA, and activity of cellulase and pectinase. The effective isolate was identified as Bacillus cereus. This strain also colonized root of rice seedlings and increased root fresh weight (31.4%) and shoot dry weight (28.2%) in vitro. These results showed that endorhiza of rice harbors effective antagonistic bacteria with multiple PGP traits which can be used as a potent biocontrol or biopromoting agent in rice plant.

Empowering rice seedling growth by endophytic Bradyrhizobium sp. SUTN9-2.

Bradyrhizobium sp. strain SUTN9-2 was confirmed as rice endophytic bacteria and also as rice growth promotion agent. SUTN9-2 showed the capability of plant growth promotion characteristics, such as indole-3-acetic acid (IAA) and 1-amino-cyclopropane-1-carboxylic acid (ACC) deaminase productions and nitrogen fixation. In this study, the ability of SUTN9-2 to stimulate rice growth was investigated at different stages with N-free and NH4 NO3 under invivo condition. The rice dry weight and chlorophyll content could be enhanced when SUTN9-2 was inoculated in N-free, especially at seedling stage (7 and 14 dai). The rice dry weight was also increased when SUTN9-2 was inoculated with NH4 NO3 at 7 and14 dai. The results of quantitative analysis of IAA and ACC deaminase were inconsistent with the expression of genes involved in IAA (nit) and ACC deaminase (acdS) productions. This inconsistently could implied that IAA and ACC deaminase produced from SUTN9-2 do not directly affect rice growth, but other factors resulting from the production of IAA and ACC deaminase could be involved. Moreover, the expression of genes involved in nitrogen fixation (nifH and nifV) of SUTN9-2 was also induced in rice tissues. This finding suggested that rice growth promotion may be supported by NH4 NO3 together with nitrogen fixation by SUTN9-2. SIGNIFICANCE AND IMPACT OF THE STUDY: Indole-3-acetic acid, 1-amino-cyclopropane-1-carboxylic acid deaminase productions and nitrogen fixation may play important roles in rice growth promotion by endophytic SUTN9-2, especially at early rice seedling growth stage, which has the potential to be used as rice seedling growth promoter in the system of rice intensification.

Effect of maize root exudates on indole-3-acetic acid production by rice endophytic bacteria under influence of L-tryptophan

Background: It is assumed that plant growth regulators produced by beneficial bacterial species could also influence plant growth. IAA is a major plant growth regulator responsible for stimulation of plant growth. There are several microorganisms which are naturally responsible for L- tryptophan metabolism. Methods: In total, 56 indigenous morphologically distinct isolates from rice roots were selected and subsequently characterized with biochemical tests, 16S rRNA sequencing and plant growth promoting activities. Pseudomonas fluorescens RE1 (GenBank: MF102882.1) and RE17 (GenBank: MF103672.1) endophytes resulted in better PGP activity against the other 54 isolates. Both endophytes were tested to screen indole-3-acetic acid production ability in pure culture conditions with L-tryptophan at 0, 50, 100, 200 and 500µg/ml concentrations. Results: P. fluorescens RE1 was recorded efficient for indole production in comparison to P. fluorescens RE17 at various L-tryptophan concentrations. P. fluorescens RE1 was shown to produce between 0.8 µg/ml and 11.5µg/ml of indole at various tryptophan concentrations, while RE17 produced between 1.2µg/ml and 10.2µg/ml. At 200 and 500µg/ml tryptophan concentration, P. fluorescens RE17 produced 7.4pmol/ml and 9.3pmol/ml IAA, respectively. Conclusions: Inoculation of maize seed with P. fluorescens RE1 and RE17 showed a significantly higher level of IAA production in comparison to non-inoculated seeds. Current study outcomes proved that plant growth regulators produced by Pseudomonas species could also play a critical role in plant growth promotion.

Effect of maize root exudates on indole-3-acetic acid production by rice endophytic bacteria under influence of L-tryptophan.

Background: It is assumed that plant growth regulators produced by beneficial bacterial species could also influence plant growth. IAA is a major plant growth regulator responsible for stimulation of plant growth. There are several microorganisms which are naturally responsible for L- tryptophan metabolism. Methods: In total, 56 indigenous morphologically distinct isolates from rice roots were selected and subsequently characterized with biochemical tests, 16S rRNA sequencing and plant growth promoting activities. Pseudomonasfluorescens RE1 (GenBank: MF102882.1) and RE17 (GenBank: MF103672.1) endophytes resulted in better PGP activity against the other 54 isolates. Both endophytes were tested to screen indole-3-acetic acid production ability in pure culture conditions with L-tryptophan at 0, 50, 100, 200 and 500µg/ml concentrations. Results: P.fluorescens RE1 was recorded efficient for indole production in comparison to P. fluorescens RE17 at various L-tryptophan concentrations. P. fluorescens RE1 was shown to produce between 0.8 µg/ml and 11.5µg/ml of indole at various tryptophan concentrations, while RE17 produced between 1.2µg/ml and 10.2µg/ml. At 200 and 500µg/ml tryptophan concentration, P. fluorescens RE17 produced 7.4pmol/ml and 9.3pmol/ml IAA, respectively. Conclusions: Inoculation of maize seed with P. fluorescens RE1 and RE17 showed a significantly higher level of IAA production in comparison to non-inoculated seeds. Current study outcomes proved that plant growth regulators produced by Pseudomonas species could also play a critical role in plant growth promotion.

Glimpse into the Genomes of Rice Endophytic Bacteria: Diversity and Distribution of Firmicutes.

Glimpse into the Genomes of Rice Endophytic Bacteria: Diversity and Distribution of Firmicutes.

Diversity and functional characterization of bacterial endophytes dwelling in various rice (Oryza sativa L.) tissues, and their seed-borne dissemination into rhizosphere under gnotobiotic P-stress

Endophytic bacterial diversity in four rice cultivars grown in two soil-types, their plant-probiotic features and rhizospheric deployment under P-stress were investigated. Oryza sativa cvs. TCN1, TCS10, TK8, and TN71 were cultivated in greenhouse using non-sterile acidic and near-neutral paddy soils for 60 days. Root, stem and leaf tissues were screened for culturable bacterial endophytes using nutrient agar. Endophytes were identified and profiled for plant-probiotic features. The richness, Shannon-Weiner diversity, evenness and Venn’s distribution in terms of endophytic strains were evaluated. Seed-borne endophytes were characterized through DGGE. The deployment of endophytes into the rhizosphere in TCN1 and TK8 under gnotobiotic P-stress was assessed. A total of 52 distinct endophytic bacterial strains affiliated to 5 classes and 20 discrete genera exhibiting differential plant-probiotic features were isolated from various tissues of four different rice cultivars. The diversity and distribution of endophytes fluctuated with soil-type, tissue-type and rice genotype. Gnotobiotic insoluble P treatment revealed significantly enhanced deployment of P-solubilizing rhizobacteria in TCN1 as compared to soluble P and P-lacking control. Rice endophytic bacteria are diverse, and their distribution within the plant and deployment as rhizobacteria were found to be influenced by host genotype, edaphic factors and nutrient stress.