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A total of 120 rhizobacteria were isolated from seven different tea estates of Darjeeling, West Bengal, India. Based on a functional screening of in vitro plant growth-promoting (PGP) activities, thirty potential rhizobacterial isolates were selected for in-planta evaluation of PGP activities in rice and maize crops. All the thirty rhizobacterial isolates were identified using partial 16S rRNA gene sequencing. Out of thirty rhizobacteria, sixteen (53.3%) isolates belong to genus Bacillus, five (16.6%) represent genus Staphylococcus, three (10%) represent genus Ochrobactrum, and one (3.3%) isolate each belongs to genera Pseudomonas, Lysinibacillus, Micrococcus, Leifsonia, Exiguobacterium, and Arthrobacter. Treatment of rice and maize seedlings with these thirty rhizobacterial isolates resulted in growth promotion. Besides, rhizobacterial treatment in rice triggered enzymatic [ascorbate peroxidase (APX), catalase (CAT), chitinase, and phenylalanine ammonia-lyase (PAL)], and non-enzymatic [proline and polyphenolics] antioxidative defense reactions indicating their possible role in the reduction of reactive oxygen species (ROS) burden and thereby priming of plants towards stress mitigation. To understand such a possibility, we tested the effect of rhizobacterial consortia on biotic stress tolerance of rice against necrotrophic fungi, Rhizoctonia solani AG1-IA. Our results indicated that the pretreatment with rhizobacterial consortia increased resistance of the rice plants towards the common foliar pathogen like R . solani AG1-IA. This study supports the idea of the application of plant growth-promoting rhizobacterial consortia in sustainable crop practice through the management of biotic stress under field conditions.

Plant growth-promoting rhizobacteria (PGPR) offer an eco-friendly alternative to agrochemicals for better plant growth and development. Here, we evaluated the plant growth promotion abilities of actinobacteria isolated from the tea (Camellia sinensis) rhizosphere of Darjeeling, India. 16 S rRNA gene ribotyping of 28 isolates demonstrated the presence of nine different culturable actinobacterial genera. Assessment of the in vitro PGP traits revealed that Micrococcus sp. AB420 exhibited the highest level of phosphate solubilization (i.e., 445 ± 2.1 µg/ml), whereas Kocuria sp. AB429 and Brachybacterium sp. AB440 showed the highest level of siderophore (25.8 ± 0.1%) and IAA production (101.4 ± 0.5 µg/ml), respectively. Biopriming of maize seeds with the individual actinobacterial isolate revealed statistically significant growth in the treated plants compared to controls. Among them, treatment with Paenarthrobacter sp. AB416 and Brachybacterium sp. AB439 exhibited the highest shoot and root length. Biopriming has also triggered significant enzymatic and non-enzymatic antioxidative defense reactions in maize seedlings both locally and systematically, providing a critical insight into their possible role in the reduction of reactive oxygen species (ROS) burden. To better understand the role of actinobacterial isolates in the modulation of plant defense, three selected actinobacterial isolates, AB426 (Brevibacterium sp.), AB427 (Streptomyces sp.), and AB440 (Brachybacterium sp.) were employed to evaluate the dynamics of induced systemic resistance (ISR) in maize. The expression profile of five key genes involved in SA and JA pathways revealed that bio-priming with actinobacteria (Brevibacterium sp. AB426 and Brachybacterium sp. AB440) preferably modulates the JA pathway rather than the SA pathway. The infection studies in bio-primed maize plants resulted in a delay in disease progression by the biotrophic pathogen Ustilago maydis in infected maize plants, suggesting the positive efficacy of bio-priming in aiding plants to cope with biotic stress. Conclusively, this study unravels the intrinsic mechanisms of PGPR-mediated ISR dynamics in bio-primed plants, offering a futuristic application of these microorganisms in the agricultural fields as an eco-friendly alternative.

Biological control is a promising approach to enhance pathogen and pest control to ensure high productivity in cash crop production. Therefore, PGPR biofertilizers are very suitable for application in the cultivation of tea plants ( Camellia sinensis ) and tobacco, but it is rarely reported so far. In this study, production of a consortium of three strains of PGPR were applied to tobacco and tea plants. The results demonstrated that plants treated with PGPR exhibited enhanced resistance against the bacterial pathogen Pseudomonas syringae (PstDC3000). The significant effect in improving the plant's ability to resist pathogen invasion was verified through measurements of oxygen activity, bacterial colony counts, and expression levels of resistance-related genes ( NPR1 , PR1 , JAZ1 , POD etc.). Moreover, the application of PGPR in the tea plantation showed significantly reduced population occurrences of tea green leafhoppers ( Empoasca onukii Matsuda ), tea thrips ( Thysanoptera:Thripidae ), Aleurocanthus spiniferus ( Quaintanca ) and alleviated anthracnose disease in tea seedlings. Therefore, PGPR biofertilizers may serve as a viable biological control method to improve tobacco and tea plant yield and quality. Our findings revealed part of the mechanism by which PGPR helped improve plant biostresses resistance, enabling better application in agricultural production.

Caffeine is a defensive alkaloid primarily accumulated in tea leaves to defend against pathogens. But the regulatory mechanism for caffeine biosynthesis in response to fungal infection and the trade‐off between specialised metabolite and plant growth remain elusive. Here, we report that jasmonic acid (JA)‐regulated CsMYB184 is the key for caffeine biosynthesis in tea leaves. Exogenous MeJA promoted caffeine biosynthesis in tea leaves and enhanced the resistance against fungal pathogens. JASMONATE ZIM‐domain proteins (JAZs) interacted with CsMYB184 to repress CsMYB184 transactivation of TCS1. Meanwhile, JA effector CsMYC2 directly bound to and activated CsMYB184 transcription, but inhibited plant growth by directly modulating GA inactivation through gibberellin 2‐oxidase 4 (CsGA2ox4). By contrast, gibberellins (GA) stimulated tea plant growth and inhibited caffeine biosynthesis, rendering tea plants more susceptible to fungal pathogens, via competitive DELLA proteins interacting with JAZs to relieve JAZ inhibition of CsMYB184. CsDELLA‐JAZ‐MYC2‐MYB184‐TCS1 formed an activation–repression loop to regulate developmental and hormonal control of caffeine biosynthesis in response to fungal pathogens, which balance the tea plant growth and defence response trade‐offs. The study reveals JA‐GA antagonistic regulation of caffeine biosynthesis as one of the innate immunity defences, meanwhile balancing the growth and defence of tea plants via crosstalk between JA and GA signalling.

Background Adventitious root (AR) formation is the key step for successful cutting propagation of tea plants ( Camellia sinensis L.). Studies showed that arbuscular mycorrhizal fungus (AMF) can promote the rooting ability, and auxin pathway in basal stem of cuttings was involved in this process. However, auxin and abscisic acid (another important regulator on AR formation) in the other parts of cuttings at different rooting stages responding to AMF inoculation are not well studied. Therefore, in this paper, contents, enzymes and genes related to these two plant hormones were comprehensively determined aiming to unveil how endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA) involve in the AMF regulating AR development of tea cuttings. Results Inoculating with AMF significantly increased the proportion of cuttings at S2 stage (AR formation), which was more than twice as much as the control. And the total rooting rate in mycorrhizal treatment was also higher than that in the control with an increase of 8.66%. Enzyme activity assays showed that except for decreased polyphenol oxidase (PPO) activity at the S3 stage and peroxidase (POD) activity in middle stem of S3 stage, AMF inoculation increased activities of POD, PPO, superoxide dismutase (SOD) and catalase (CAT) to varying degrees in leaf, middle stem and basal stem of tea cuttings. After inoculation with AMF, the indoleacetic acid oxidase (IAAO) activity decreased to a certain extent in the first three stages of tea cuttings, which showed a trend of ‘low-high-low’ in the basal stem of all treatments. Besides, there was a significantly positive correlation between SOD activity and AR formation, especially for the proportion of cuttings at S2 and S3 stages. Higher IAA level and IAA/ABA ratio was found in basal stem of cuttings at S1 stage induced by AMF, which promoting the AR formation as revealed by correlation analysis. At the same time, AMF significantly elevated the level of IAA in leaf at S1 stage. By screening differentially expressed genes (DEGs) related to IAA and ABA pathways, together with redundant analysis, it was indicated that auxin biosynthesis and transport, as well as ABA transport and signal transduction, were involved in AMF regulating the rooting of tea cuttings. Conclusions Overall, both endogenous IAA and ABA played roles in the regulation of AR formation of tea cuttings by AMF inoculating, enriching the theoretical basis of AMF regulating rooting of cuttings and providing foundations for cutting propagation of tea plants.

Anthracnose caused by Colletotrichum is one of the most severe diseases that can afflict Camellia sinensis . However, research on the diversity and geographical distribution of Colletotrichum in China remain limited. In this study, 106 Colletotrichum isolates were collected from diseased leaves of Ca. sinensis cultivated in the 15 main tea production provinces in China. Multi-locus phylogenetic analysis coupled with morphological identification showed that the collected isolates belonged to 11 species, including 6 known species ( C. camelliae , C. cliviae , C. fioriniae , C. fructicola , C. karstii , and C. siamense ), 3 new record species ( C. aenigma , C. endophytica , and C. truncatum ), 1 novel species ( C. wuxiense ), and 1 indistinguishable strain, herein described as Colletotrichum sp. Of these species, C. camelliae and C. fructicola were the dominant species causing anthracnose in Ca. sinensis . In addition, our study provided further evidence that phylogenetic analysis using a combination of ApMat and GS sequences can be used to effectively resolve the taxonomic relationships within the C. gloeosporioides species complex. Finally, pathogenicity tests suggested that C. camelliae , C. aenigma , and C. endophytica are more invasive than other species after the inoculation of the leaves of Ca. sinensis .

Background The experimental materials were a 60-year-old tea tree ( Camellia sinensis cv. Shu Cha Zao; SCZ) (the mother plant) and 1-year-old and 20-year-old plants of SCZ that originated as mother plant cuttings. The aim of this study was to use high-throughput sequencing to study the spatial and dynamic distribution of endophytic fungi in different leaf niches (upper leaves, middle leaves, lower leaves) and rhizosphere soil on tea plants of different ages in the same garden. Results Ascomycota (83.77%), Basidiomycota (11.71%), and Zygomycota (3.45%) were the dominant fungal phyla in all samples. Cladosporium (12.73%), Zymoseptoria (9.18%), and Strelitziana (13.11%) were the dominant genera in the leaf. Alpha diversity analysis revealed that endophytic communities in leaves differed from those in rhizosphere soil and different leaf niches had similar fungal diversity. Shannon’s indices and NMDS analysis indicated significant differences in fungal diversity and composition among the SCZ trees of different ages ( p  ≤ 0.01). The abundance of Cladosporium and Zymoseptoria decreased with increasing SCZ age, whereas the abundance of Strelitziana increased. Conclusions The results illustrate variation in endophytic fungi among different niches on tea plants of different ages. The distribution of endophytic fungi in leaves of C. sinensis shows spatiotemporal variation.

To unravel the molecular mechanism of defense against blister blight (BB) disease caused by an obligate biotrophic fungus, Exobasidium vexans , transcriptome of BB interaction with resistance and susceptible tea genotypes was analysed through RNA-seq using Illumina GAIIx at four different stages during ~20-day disease cycle. Approximately 69 million high quality reads were assembled de novo , yielding 37,790 unique transcripts with more than 55% being functionally annotated. Differentially expressed, 149 defense related transcripts/genes, namely defense related enzymes, resistance genes, multidrug resistant transporters, transcription factors, retrotransposons, metacaspases and chaperons were observed in RG, suggesting their role in defending against BB. Being present in the major hub, putative master regulators among these candidates were identified from predetermined protein-protein interaction network of Arabidopsis thaliana . Further, confirmation of abundant expression of well-known RPM1, RPS2 and RPP13 in quantitative Real Time PCR indicates salicylic acid and jasmonic acid, possibly induce synthesis of antimicrobial compounds, required to overcome the virulence of E. vexans . Compendiously, the current study provides a comprehensive gene expression and insights into the molecular mechanism of tea defense against BB to serve as a resource for unravelling the possible regulatory mechanism of immunity against various biotic stresses in tea and other crops.

Camellia sinensis is an important economic plant grown in southern subtropical hilly areas, especially in China, mainly for the production of tea. Soil acidification is a significant cause of the reduction of yield and quality and continuous cropping obstacles in tea plants. Therefore, chemical and microbial properties of tea growing soils were investigated and phenolic acid-degrading bacteria were isolated from a tea plantation. Chemical and ICP-AES investigations showed that the soils tested were acidic, with pH values of 4.05–5.08, and the pH negatively correlated with K (p < 0.01), Al (p < 0.05), Fe and P. Aluminum was the highest (47–584 mg/kg) nonessential element. Based on high-throughput sequencing, a total of 34 phyla and 583 genera were identified in tea plantation soils. Proteobacteria and Acidobacteria were the main dominant phyla and the highest abundance of Acidobacteria was found in three soils, with nearly 22% for the genus Gp2. Based on the functional abundance values, general function predicts the highest abundance, while the abundance of amino acids and carbon transport and metabolism were higher in soils with pH less than 5. According to Biolog Eco Plate™ assay, the soil microorganisms utilized amino acids well, followed by polymers and phenolic acids. Three strains with good phenolic acid degradation rates were obtained, and they were identified as Bacillus thuringiensis B1, Bacillus amyloliquefaciens B2 and Bacillus subtilis B3, respectively. The three strains significantly relieved the inhibition of peanut germination and growth by ferulic acid, p-coumaric acid, p-hydroxybenzoic acid, cinnamic acid, and mixed acids. Combination of the three isolates showed reduced relief of the four phenolic acids due to the antagonist of B2 against B1 and B3. The three phenolic acid degradation strains isolated from acidic soils display potential in improving the acidification and imbalance in soils of C. sinensis.

Drought can seriously affect the yield and quality of tea. The interaction between rhizosphere microorganisms and tea plants could enhance the drought resistance of tea plants. However, there are few studies on the effects of abundant and rare microorganisms on tea plants. In this study, the contributions of abundant and rare bacteria in the rhizosphere microorganisms of ‘FudingDabaicha’ and ‘Baiye No.1’ to the resistance of tea plants to drought stress were studied using 16SrRNA sequencing, co-occurrence network analysis, and PLS-PM modeling analysis. By measuring the contents of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), malondialdehyde (MDA), proline, soluble sugar and soluble protein, it was found that the activity of antioxidant enzymes and the content of osmotic substances increased significantly after drought stress ( p  < 0.001). In the co-occurrence network of the two varieties, the average degree, clustering coefficient, and modularity index of the rare bacteria were greater than those of the abundant bacteria, and the path coefficient of the rare bacteria to drought was greater than that of the abundant bacteria. The contribution of rare microorganisms in ‘FudingDabaicha’ to drought stress was greater than that in ‘Baiye No.1’. The rare bacteria of the two varieties were positively correlated with amino acids and negatively correlated with lipids. The results of this study will provide new insights for the use of rhizosphere microorganisms in improving the drought resistance of tea plants.