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Item Nodule associated bacteria for plant growth promotion and nodulation enhancement in cowpea (Vigna unguiculata (L.) Walp(Department of Agricultural Microbiology, College of Agriculture, Vellayani, 2026) Jaiba EvansThe study entitled ‘Nodule associated bacteria for plant growth promotion and nodulation enhancement in cowpea (Vigna unguiculata (L.) Walp)’ was carried out at the Department of Agricultural Microbiology, College of Agriculture, Vellayani, Thiruvananthapuram, with the objective to isolate and characterize nodule associated bacteria from different varieties of cowpea and assess their nodulation efficiency and plant growth promotion in cowpea (Vigna unguiculata (L.) Walp). Root nodules of leguminous plants harbour diverse microbial communities that play crucial roles in nitrogen fixation and plant growth promotion. In this study, nodule- associated bacteria were isolated from healthy root nodules collected from different varieties of cowpea from various locations in the (AEU 8) southern laterites of Kerala. Surface-sterilized nodules were crushed aseptically, and the suspension was serially diluted and plated on different media including Yeast Extract Mannitol Agar (YEMA), Nutrient agar, N free malate bromothymol blue media, Tryptic soy agar, Burk’s medium, Jensen’s medium. The seventy-four isolates were purified and characterized based on colony morphology and Gram reaction. Of these, thirty-four morphologically distinct isolates were selected for further studies. The Indole Acetic Acid (IAA), Gibberellic acid (GA), Extracellular Ammonia (ECA) production, presence or absence of growth on N-free medium, phosphate solubilization potential and cellulolytic activity of the thirty-four bacterial isolates were assessed. The selected isolates produced IAA in the range of 2.64 μg mL-1 (NAB 57) to 63.98 μg mL-1 (NAB 1) of culture filtrate in the absence of tryptophan and 5.12 μg mL- 1 (NAB 63) to 98.18 μg mL-1 (NAB 1) in the presence of tryptophan. The isolate NAB 42 recorded significantly higher gibberellic acid production of 62.24 μg mL-1 and NAB 14 recorded highest extracellular ammonia production of 11.29 μmol mL−1. The isolate NAB 43 exhibited maximum cellulolytic activity of 5.45 and NAB 57 showed maximum phosphate solubilization potential of 4.6. Among these isolates NAB 1, NAB 2, NAB 42 and NAB 43 were showed growth on N-free medium. Plant growth promotion potential in cowpea was assessed by roll towel assay using standard protocol and NAB 2 exhibited the highest germination rate of 85.3% and longest root length (22.78 cm), while NAB 15 demonstrated the longest shoot length (19.81cm). The highest seedling vigour index (4121.5) was recorded for NAB 2, compared to 2223.75 in the control. Weighted average ranking was done and eleven isolates were selected for further experiments. Selected isolates were co-cultured with beneficial microbes, including rhizobial and non-rhizobial endophytes, to assess compatibility and mutual influence on growth and metabolic activity. The combinations exhibited compatibility with each other and with other beneficial microbes. Dual culture plate assay and agar well diffusion assay were employed to assess the antagonistic potential of the 34 isolates against Pythium sp., Fusarium oxysporum, Sclerotium rolfsii, and Rhizoctonia solani. Isolates NAB 51 and NAB 27 showed the maximum inhibitory activity against Fusarium oxysporum, while NAB 27 was most effective against Rhizoctonia solani. NAB 33 exhibited the maximum inhibition against Sclerotium rolfsii, and NAB 42 showed maximum antagonistic activity against Pythium sp. The maximum siderophore production was observed in NAB 2 as indicated by orange halo zone around the colony on CAS agar. All isolates produced volatile organic compounds, with NAB 2 exhibiting the maximum level and only one isolate NAB 43 tested positive for hydrogen cyanide (HCN) production. The growth performance and nodulation efficiency of the test cowpea plants were evaluated under controlled conditions using Leonard’s jar assemblies. Inoculated treatments with Rhizobium exhibited a marked improvement in growth and nodulation parameters compared to uninoculated controls. Among the isolates, strain NAB 2 recorded the significant increase in plant height (30.25 cm), root length (19.2 cm), shoot weight (4.35g), root weight (0.76g), nodule number (16), nodule weight (0.07g) compared to uninoculated controls, indicating effective symbiotic performance. Based on the results of the studies on plant growth promotion and nodulation enhancement, the isolates NAB 2 and NAB 43 were selected for pot culture experiment. Morphological and biochemical characterization of the isolates revealed that the two isolates were Gram-negative, rods. The 16S rRNA gene sequencing showed maximum sequence similarity of the isolates with Stenotrophomonas hibscicola (NAB 2) and Enterobacter quasiroggenkampii (NAB 43). A pot culture experiment was carried out to assess the effectiveness of selected nodule-associated bacterial (NAB) isolates, both individually and in combination with Rhizobium, in promoting plant growth and improving nodulation in cowpea variety Anaswara by seed biopriming. The experimental design was Completely Randomized Design (CRD) with six treatments, each replicated four times. Among the NAB isolates, Stenotrophomonas hibiscicola NAB 2 in combination with Rhizobium sp. showed superior performance, significantly enhancing plant growth, yield, and nodulation parameters. This treatment resulted in the highest plant height, leaf and branch number, shoot and root biomass, root development, pod yield, and nodule number and weight, indicating its strong potential for improving crop productivity. The study concluded that the selected nodule-associated bacterial isolate NAB 2, particularly when used in combination with Rhizobium sp., significantly enhanced plant growth and nodulation in cowpea var. Anaswara. These findings suggest that co- inoculation of Stenotrophomonas hibscicola NAB 2 with Rhizobium sp. RZB1 can serve as an effective bioinoculant strategy to improve legume productivity and promote sustainable agriculture.Item Multifunctional microbial consortium for bio- enriched compost(Department of Agricultural microbiology, College of Agriculture, Vellayani, 2026) Aiswarya PrasanthThe research work on “Multifunctional microbial consortium for bio-enriched compost” was performed at the Department of Agricultural Microbiology, College of Agriculture, Vellayani, Thiruvananthapuram during 2024-2025, with the objective of developing a lignocellulolytic microbial consortium with plant growth promotion potential for conversion of agricultural residues to bio-enriched compost. Microorganisms capable of decomposing lignin, hemicellulose and cellulose in plant material can be effectively used for the management of agricultural residues. Many lignocellulolytic microorganisms possess the ability to promote plant growth by enhancing the nutrient supply and supplying plant growth hormones. Ten lignocellulolytic bacterial isolates obtained from two previous studies were procured from the Department of Agricultural Microbiology and screened for lignocellulolytic potential and plant growth promotion ability. The isolates with superior lignocellulolytic activity and PGP activities were checked for compatibility and used for composting of banana residues. The potential of the resultant bio-enriched compost for supporting plant growth was evaluated by pot culture studies using red amaranthus var. Vaika. Among the ten isolates tested, isolate M1045 recorded the highest cellulolytic index (5.86) and CLSD07 exhibited the maximum ligninolytic index (5.77). Carboxymethyl cellulase (CMCase) activity of the isolates ranged from 3.43 to 9.88 U mL⁻¹ min⁻¹, with M1045 showing the highest activity, followed by CLSD07. Filter paper cellulose (FPase assay) activity was maximum in CLSD07 (2.56 U mL⁻¹ min⁻¹) which was followed by M1045 (2.40 U mL⁻¹ min⁻¹) after 96 h of incubation. Laccase activity peaked in CLSM03 (1.53 U mL⁻¹) and CLSM02 (1.39 U mL⁻¹), while lignin peroxidase and manganese peroxidase were maximally produced by M1045 (18.60 and 3.56 U mL⁻¹, respectively). All isolates synthesized indole-3-acetic acid (IAA), with CLSD07 producing the highest amount (55.36 μg mL⁻¹ in the presence of the precursor, tryptophan). Gibberellic acid production was highest in M1045 (98.54 μg mL⁻¹), followed by G1051 (84.11 μg mL⁻¹). Extracellular ammonia production was maximum in CLSD07 (7.46 μmol mL⁻¹). Six isolates were capable of solubilizing inorganic phosphate in NBRIP medium, with M1045 showing the highest phosphate solubilization index (2.87), followed by G1051 (2.67). Both M1045 and CLSD07 produced siderophores, and four isolates demonstrated antagonistic activity against Rhizoctonia solani, with G1051 showing the greatest inhibition (40.23% over control), followed by W1048 (36.48%). Compatibility analysis revealed that the best performing isolates M1045, CLSD07, W1048, and G1051 exhibited no mutual inhibition, confirming their suitability for consortium development. Morphological and biochemical characterization of the isolates revealed that all the five isolates were Gram-positive, endospore-forming rods. The 16S rRNA gene sequencing showed maximum sequence similarity of the isolates with Calidifontibacillus erzurumensis (M1045), Bacillus velezensis (CLSD07) and Bacillus spp. (W1048 and G1051). The microbial consortium prepared from these isolates was evaluated for its composting efficiency. The four bacterial isolates were cultured in nutrient broth and consortium was prepared by mixing equal volumes of all four isolates. The consortium (~1x108 cfu mL-1) was sprayed over banana residue chopped into small pieces at the rate of 0.1%, 0.2% and 0.5% (v/w). The treatment with 0.5% consortium (T₃) achieved rapid decomposition, attaining the highest temperature (48.2°C) during the fourth week, lowest C:N ratio (12.70:1) by the ninth week, minimum moisture content (21.54%), and lowest bulk density (0.185 g cm⁻³). The resulting compost was nutrient-enriched, with elevated levels of nitrogen (1.41%), phosphorus (0.43%), potassium (1.28%), zinc (14.65 mg kg⁻¹), and copper (53.75 mg kg⁻¹), while heavy metals remained below detectable limits, ensuring safety for agricultural use. However, the C:N ratio fell below 20:1 at the 5th week itself, which is the level acceptable for compost for agricultural purpose. From the initial screening, the treatment with 0.5% microbial consortium (T1) was identified as the most effective based on rapid decomposition rate and minimum time required to attain a lower C:N ratio. The selected treatment was therefore used for subsequent studies comparing its performance with an uninoculated control. The compost used for pot culture studies was prepared by mixing 0.5% v/w of bacterial consortiumwith 600 kg of banana residue. This treatment showed improved compost quality, registering a temperature of 68.64°C during the third week, pH of 7.81, EC of 2.71 dS m⁻¹, and a reduced C:N ratio of 13.05:1, with enhanced nutrient status (N 1.31%, P 0.466%, K 1.243%, Zn 15.01 mg kg⁻¹). Application of bio-enriched compost significantly improved seed germination (96.5%) and germination index (106.3) in red amaranthus. The treatment T1 – bio-enriched compost markedly enhanced growth attributes, including plant height (52.43 cm), number of leaves (57), branches (8.33), and root length compared to control. Overall, the lignocellulolytic bacterial consortium with plant growth promotion potential demonstrated superior composting efficiency, producing a nutrient-rich, agriculturally safe compost that promoted plant growth and could serve as a sustainable alternative to chemical fertilizers.Item Plant growth promotion and foot rot disease management in black pepper by bacillus spp.(Department of Agricultural Microbiology, College of Agriculture, Vellayani, 2022-02-11) Anju, A B; Anith, K NThe study named “Plant growth promotion and foot rot disease management in black pepper by Bacillus spp.” was conducted in Department of Agricultural Microbiology, College of Agriculture, Vellayani and Coconut Research Station, Balaramapuram, during the academic year 2019-2022. The objective of the study was to assess the effects of endospore-forming Bacillus spp. on growth and foot rot disease suppression in black pepper in the nursery. Experiments comprised both in vitro and in vivo studies. In in vitro interaction, dual culture plate assay was done to assess the antagonistic effect of bacterial isolates against P. capsici. All the three bioagents used were proven to be antagonistic to P. capsici. B. pumilus VLY17 showed the maximum zone of inhibition whereas B. amyloliquefaciens VLY27 showed the least zone of inhibition. No inhibition on mycelial growth of P. capsici was observed on treatment with culture filtrate in agar well diffusion assay. In detached leaf assay screening, significant difference was observed in lesion size developed on leaves treated with bacterial suspension compared to that on control leaves treated with sterile water. On 2DAI, leaves dipped in B. pumilus VLY17 showed the least lesion size whereas on 3 DAI, leaves applied with consortium of the bacterial isolates showed the least lesion size. Bio agents were characterized to check the production of plant growth promoting and disease suppressing metabolites. All the three isolates showed significant amount of IAA production. B. velezensis PCSE10 produced higher IAA (15.10 ppm) when estimated without adding tryptophan whereas B. amyloliquefaciens VLY27 produced maximum IAA (23.34 ppm) when medium was supplemented with L-Tryptophan. None of the strains could produce HCN under in vitro conditions. B. amyloliquefaciens VLY27 and B. velezensis PCSE10 used produced Ammonia. None of the bacterial isolates used showed siderophore production and phosphate solubilization. Bacterization with B. pumilus VLY17 showed the maximum establishment of cuttings, maximum number of leaves per plant, maximum shoot length and longest root length, maximum root volume and maximum fresh weight and dry weight of newly emerged shoot and leaves as well as roots throughout the experimental duration. Even though fresh weight of roots increased on bacterization, no significant difference was observed in statistical analysis compared to control. Plants treated with B. amyloliquefaciens VLY27 showed the maximum number of roots per plant. Suppression of Phytophthora foliar infection on bacterization was evaluated in the nursery. On analysis significant difference was observed in lesion size on treatment with bacterial suspension compared to pathogen inoculated control. The least lesion size was observed on treatment with B. pumilus VLY17. The treatments also showed significant effect on disease index. Abundance of root colonization by endospore forming bacterial isolates was checked to ascertain if the plant growth promotion as well as the disease suppression was brought about by the endospore-forming bacterial isolates. Colonization of endospore formers was found to be maximum on roots of plants treated with consortium of bacterial isolates. From the present study, it is concluded that endospore-forming bacteria used in the study have plant growth promotional activities and biocontrol potential against the pathogen P. capsici, which causes foot rot in black pepper.Item Optimization of biopolymers for seed biopriming in rice (Oryza sativa L.)(Department of Agricultural Microbiology, College of Agriculture, Vellanikkara, 2025-01-24) Deepna, E P.; Panchami, P SSeed biopriming is a novel, cost-effective method that applies beneficial microbial inoculants directly to the seed surface, enhancing seed growth and overall agricultural production. The technique of incorporating biopolymers as a thin, protective film around the seed without altering its size or shape has emerged as a recent trend.These biopolymers help to maintain microbial stability and activity, providing a favorable environment for the inoculants. The present study entitled “Optimization of biopolymers for seed biopriming in rice (Oryza sativa L.)” aimed to develop rice seeds coated with biopolymers and beneficial microbes to enhance growth and yield in rice, as well as to improve seed quality and longevity of bioprimed seeds. The study focused on standardization of the concentrations and imbibition times of biopolymers and bioagents for effective biopriming and evaluation of their effect on plant growth. The study evaluated five biopolymers viz., chitosan, sodium alginate, lignosulfonate, guar gum, and maltodextrin combined with Bacillus subtilis and Azospirillum zeae for seed biopriming in rice. Bioagents compatibility studies confirmed that B. subtilis and A. zeae were compatible, with no inhibition in their growth. Biopolymer and seed compatibility was assessed by imbibing rice seeds in 0.5%, 1%, and 2% biopolymer solutions for 1 h and 24 h, with 1 h imbibition yielding better results than 24 h. Among the different biopolymers used, 0.5% sodium alginate was the most effective, with highest germination rate (83.3%), seedling length (5.98 cm), and seedling vigor index (498) in rice. The incubation of bioagents in biopolymer solutions showed no inhibition in their growth, confirming the compatibility between all the biopolymers and bioagents tested. Based on the compatibility studies, the biopolymer concentrations standardized for seed biopriming in rice were 1% chitosan, 0.5% sodium alginate, 1% lignosulfonate, 0.5% guar gum, and 0.5% maltodextrin, along with a 1 h imbibition time. The coating efficiency of biopolymer with bioagent consortia (Bacillus subtilis + Azospirillum zeae) showed that rice seeds coated with 0.5% sodium alginate maintained the highest population of Bacillus subtilis (42.8 × 10⁸ cfu/g), followed by seeds coated with lignosulfonate (38.12 × 10⁸ cfu/g) after 1h of coating. Similarly, the population of Azospirillum zeae was higher in seeds coated with bioagent consortia and lignosulfonate (27.76 × 10⁸ cfu/g), followed by sodium alginate-coated seeds (26.03 × 10⁸ cfu/g) after 1h. Scanning electron microscopy confirmed the presence of bioagents on the seed surface, while stereozoom microscopy showed no significant changes in seed size or shape. The effect of seed biopriming on plant growth revealed that rice seeds primed with bioagent consortia and 0.5 % sodium alginate achieved the highest germination rate (100%), while those with lignosulfonate showed the longest seedling length (25.78 cm) and highest seedling vigor index (2487). Additionally, a slight increase in seed weight and volume were observed after biopriming. The bioprimed seeds were stored at room temperature for 6 months, with weekly observations recorded for bioagent survival and germination percentage. After three months, a significant decline in both germination percentage and bioagent survivability were observed. However, seeds coated with bioagent consortia and 1% lignosulfonate maintained bioagent populations up to six months. Seeds coated with bioagent consortia and lignosulfonate also maintained a higher germination percentage (82.66%) even after five months of storage. In contrast, chitosan treated seeds did not showed germination after two months of storage, and bioagent population was declined after three months.The two biopolymer-based bioagent consortia formulations, bioagent consortia + 0.5% sodium alginate and bioagent consortia + 1% lignosulfonate were tested to assess their potential for enhancing the plant growth and yield in rice. The experiment was first conducted in sterile soil and then in non-sterile soil to evaluate the effectiveness of biopriming. Under sterile and non-sterile conditions, plant growth parameters such as plant height and the number of tillers per plant were on par for seeds bioprimed with sodium alginate and lignosulfonate. However, the number of grains per panicle and grain yield per plant were higher in seeds treated with bioagent consortia and lignosulfonate in both sterile and non-sterile conditions. Additionally, the seed treatment with bioagent consortia and biopolymers led to an increase in soil nutrient content, further highlighting the beneficial effects of biopriming. The present study highlights the efficacy of biopolymer-based priming in enhancing plant growth in rice, with 0.5% sodium alginate and 1% lignosulfonate, combined with bioagent consortia, showing promising results. Notably, seeds primed with 1% lignosulfonate exhibited the highest performance, significantly improving plant growth and seed viability, while also offering a cost-effective solution. Furthermore, bioprimed seeds retained viability up to six months. However, field trials are essential tovalidate these findings.Item Pink pigmented facultative methylotrophs (PPFMs) from black pepper (Piper nigrum L.) for drought stress mitigation and plant growth promotion(Department of Agricultural Microbiology, College of Agriculture,Vellayani, 2024-04-04) Yarlagadda Manju Bhargavi.; Anu Rajan, SThe study entitled “Pink Pigmented Facultative Methylotrophs (PPFMs) from black pepper (Piper nigrum L.) for drought stress mitigation and plant growth promotion" was carried out during the period from 2021-2023 in the Department of Agricultural Microbiology, College of Agriculture, Vellayani, Thiruvananthapuram, with the objective to isolate, screen and characterize Pink Pigmented Facultative Methylotrophs (PPFMs) for plant growth promotion and abiotic stress mitigation with special emphasis on drought management in black pepper (Piper nigrum L.) under Kerala conditions. The study comprised an in vitro screening experiment and a pot culture experiment with black pepper variety Karimunda. A total of 60 PPFM cultures were isolated from phyllosphere and rhizosphere by leaf imprint method and serial dilution and plating method on Ammonium Mineral Salt (AMS) agar medium supplemented with 0.5% methanol and 10 µg cycloheximide. These isolates were tentatively identified as PPFMs based on the characteristic pink pigmented colonies. Characterization of the isolates by colony morphology, gram reaction and biochemical tests were carried out. 30 PPFM isolates were selected for in vitro screening of PPFM isolates for plant growth promotion. IAA production by the different isolates of methylotrophs showed wide variations ranging from 10.02 to 51.25 µg mL-1 culture filtrate (without tryptophan) and from 10.06 to 60.00 µg mL-1 culture filtrate (with tryptophan). Maximum IAA production of 51.25 µg mL-1 and 60.00 µg mL-1 culture filtrate (without and with tryptophan, respectively) was recorded by PNPPFM 59. GA production by different isolates were ranging from 29.19 to 1.81 µg mL-1. Maximum GA production of 29.19 µg mL-1 was recorded by PNPPFM 60. Extracellular ammonia production by the different isolates of methylotrophs ranged from 1.43 to 7.07 µmol mL-1. Maximum extracellular ammonia production of 7.07 µmol mL-1 was recorded by PNPPFM 59. ACC deaminase activity production by different isolates were ranging from 0.89 to 13.94 µg mL-1. Maximum ACC deaminase activity production of 13.94 µg mL-1 was recorded by PNPPFM 60. For the assessment of drought tolerance potential, these isolates were grown in different concentrations of PEG 6000 viz. 0%, 5%, 10%, 20%, 30% and 40%. All the cultures were able to tolerate up to 30% concentration of PEG 6000. Index ranking was done to select the better performing isolates for the subsequent experiments. Consequently PNPPFM 60, PNPPFM 59 and PNPPFM 44 were selected for the pot culture experiment. The pot culture experiment was undertaken with black pepper cuttings to study the effect of PPFM isolates on plant growth promotion and drought tolerance. The experiment was laid out in CRD with 7 treatments and three replications. The treatments comprised four PPFM isolates (PNPPFM 60, PNPPFM 59, PNPPFM 44 and Ref. culture PPFM 38) and three control treatments (sterile water, uninoculated media and absolute control). These treatments were given as cutting dipping and foliar spray at 45, 75 and 90 DAP. The study revealed that PPFM isolates had significant effect on growth and establishment of black pepper cuttings. Maximum number of leaves (4.66), shoot length (28.30 cm), root length (17.70 cm), number of roots (14.66 and 138.33, primary and secondary roots respectively), fresh weight of roots (1.01 g), dry weight of roots (0.4 mg), fresh weight of newly emerged shoots and leaves (10.74 g) and dry weight of newly emerged shoots and leaves (2.96 g) were recorded with PNPPFM 60 and least was recorded with either one or more of controls. Cell membrane integrity and relative water content were highest with PNPPFM 60 on 4th as well as on 14th day. Highest chlorophyll stability index on 14th day was recorded with PNPPFM 60. Proline content (78.67 µg g-1 tissues), super oxide dismutase activity (0.45 activity g-1 min-1), catalase activity (18.48 activity g-1 tissues), peroxidase activity (47.18 activity g-1 min-1) and malondialdehyde (0.54 µmol g-1 tissues) were highest with PNPPFM 60. Considering the major drought tolerance parameters such as proline content, SOD, catalase, peroxidase and malondialdehyde, PNPPFM 60 was the best among the PNPPFM isolates tested in the pot culture experiment. The present study revealed that the isolate PNPPFM 60 (cutting dip – 1% PPFM culture broth and foliar spray – 1% culture broth at 45, 75 and 90 DAT) were effective in improving the growth parameters and drought tolerance in black pepper.Item Air Layering in selected fruit crops influenced by medium fortified with root colonizing fungi(Department of Agricultural Microbiology, College of Agriculture, Vellayani, 2023-02-15) : B Sangeetha Lakshmi; Chitra N; Viji, M MThe study entitled “Air layering in selected fruit crops influenced by medium fortified with root colonizing fungi” was conducted at the Department of Agricultural Microbiology, College of Agriculture, Vellayani during the period 2020-2022. The objective of the study was to investigate the effectiveness of air layering medium fortified with Piriformospora indica and/or Glomus fasciculatum on rooting and the establishment of layers of selected fruit crops. An initial experiment was conducted to evaluate the survival of the root colonizing fungi in air layering medium. The tomato seedlings planted in this medium showed root colonization with Piriformospora indica and/or Glomus fasciculatum showed colonization at 4 and 6 weeks after planting confirming that the fungi survive in the medium. Significant increase in IAA production was observed in tomato seedlings grown in layering medium individually inoculated with AMF and P. indica. Fruit crops viz., Guava, West Indian Cherry and Rambutan having varying percentage of rooting and establishment on air layering were selected for the study. The air layering medium fortified with Piriformospora indica (1% w/v), Glomus fasciculatum (5% w/v), combination of Piriformospora indica and Glomus fasciculatum, and IBA (1000 ppm) were used along with a control. Air-layering experiment with different treatments in Guava showed significantly higher root fresh weight and dry weight in combined inoculation of AMF and P. indica which was comparable to IBA treatment. On propagation of successful layer in polybags it was noted that the root volume of guava plants raised in laying medium fortified with P. indica, IBA and AMF (20.2,19.6 and 17.28 cm3 , respectively) were statistically on par and significantly higher compared to other treatments. Guava plants grown in air layering medium fortified with P. indica recorded the highest root fresh weight and dry weight (7.726 g and 2.49 g respectively). On observation of root colonization of fungi, it was seen that P. indica colonized only in the inoculated plants and but native AMF was found to colonize all guava plants. In similar studies in West Indian Cherry, layers grown in G. fasciculatum fortified medium recorded the highest number of primary roots, root volume (0.42 cm3 ), root fresh weight (0.406 g) and root dry weight (0.04 g). Treatment with IBA was on par with AMF treatment in the number of roots and root fresh weight. The percentage of successful layers was significantly high in the treatment combination of P. indica and AMF (86 percent). In in vivo study on establishment of rooted layers of West Indian Cherry planted in polybags, shoot length (67.4 cm), root length (51.2 cm), root volume (25.6 cm3 ), shoot fresh weight (27.666 g), dry weight (17.326 g), root fresh weight (8.26 g) and dry weight (3.956 g) were significantly higher in plants grown in air layering medium fortified with P. indica when compared to control. As in the case of Guava plants, West Indian Cherry also showed colonization by native AMF even in control plants but P. indica colonization was observed only in P. indica inoculated plants. The same sets of experiments in Rambutan revealed induction of callus formation in the wounded region two months after layering and rooting three months after air layering in medium fortified with P. indica and G. fasciculatum. Even though there was rooting, the number of successful layers were less and those rooted layers, when planted in the polybags for further study, dried off. Results of the present study suggest that fortification of air layering medium with root colonizing fungi viz., Piriformospora indica and Glomus fasciculatum can improve rooting and establishment of layers in Guava and West Indian cherry and the results are comparable to that of IBA treatment at 1000 ppmItem Development of inoculant cultures of nitrogen fixing cyanobacteria from wetland ecosystem of Vellayani(Department of Agricultural Microbiology, College of Agriculture,Vellayani, 2022-05-13) Arya, S; Chitra, NItem Evaluation of drought and acid tolerant actinomycetes for rice (Oryza sativa L.)(Department of Agricultural Microbiology, College of Agriculture, Vellanikkara, 2022) Gokul Vigneshwaran, P; Surendra Gopal, KRice (Oryza sativa L). is one of the world's most significant cereal crops. It is widely cultivated food crop in the world, providing staple food to 2.7 billion people. Rice cultivation is facing many challenges due to abiotic stresses like drought, acidity, flood and high temperature. Among the major yield-limiting biotic factors, disease management is one of the most important problems in paddy cultivation. Among the several diseases in rice, sheath blight (Rhizoctonia solani) is a fungal disease that has a high impact on the rice crop from tillering to the heading stage. Rhizospheric microbes, particularly actinomycetes have gained attention due to their ability to promote plant growth, control diseases and reduce harm to the environment. The use of actinomycetes as bio-control agents is sustainable and complementary in improving crop yield and protection that is affordable to farmers. Actinomycetes have been used to mitigate drought and acidic stress. Hence, the present study was carried out on “Evaluation of drought and acid-tolerant actinomycetes for rice (Oryza sativa L).” with the objective of plant growth-promotion and Rhizoctonia solani management under pot culture studies. Ten rhizospheric soil samples were collected from drought and acidic rice-growing areas of the Thrissur and Palakkad districts. All the actinomycetes isolates were subjected to morphological, cultural, and biochemical characterization. The actinomycetes isolates showed gram-positive reaction and varied in spore chain morphology viz., filamentous, spiral and closed spiral. In vitro screening of actinomycetes isolates for plant growth-promoting traits showed that all the actinomycetes isolates were positive for indole acetic acid production. Out of ten isolates, seven isolates were positive for the production of IAA and two isolates viz., MNT7 and CHT-1 were high indole acetic acid producers. IAA production by actinomycetes isolates ranged from 4.41 (μg/ml) to 5.99 (μg/ml). The MNT-7 (Streptomyces spinoverrucosus) isolate showed the highest IAA production (5.99 μg/ml) followed by CHT1 (5.43 μg/ml) and PTK-4 (Streptomyces spp.) (5.23 μg/ml). All the isolates fixed atmospheric nitrogen which ranged from 2.80 μg/ml to 10.50 μg/ml. The MNT-7 (Streptomyces spinoverrucosus (10.50 μg/ml), VLK-2 (9.10 μg/ml) and VER-4 (Streptomyces cellulosae) (7.70 μg/ml) isolates were the most efficient nitrogen-fixing isolates. The amount of phosphate solubilization varied between 3.28 μg/ml to 57.56 μg/ml. nine isolates showed potassium solubilization in the range of 1.86 μg/ml to 5.07 μg/ml. 134 In vitro screening of actinomycetes for antagonistic properties did not show ammonia and siderophore production. Among the ten actinomycetes isolates, MNT-7 (Streptomyces spinoverrucosus) and PTK-4 (Streptomyces spp.) isolates produced hydrogen cyanide. Only MNT-7 (Streptomyces spinoverrucosus) (71.23%) and PTK-4 (Streptomyces spp) (68.82%) isolates inhibited the growth of Rhizoctonia solani indicating their biocontrol potential. In vitro screening of actinomycetes for acidic pH and water stress tolerance showed that MNT-7 (Streptomyces spinoverrucosus) isolate was tolerant to acidic pH upto pH 3.5 and MNT-7 (Streptomyces spinoverrucosus) and PTK-4 (Streptomyces spp.)isolates were water stress tolerant upto 20 % PEG. The three most promising (MNT-7, PTK-4 and VER-4) actinomycetes were identified as Streptomyces spinoverrucosus, Streptomyces spp., Streptomyces cellulosae respectively. On the basis of the plant growth-promoting activities, acidic pH and water stress tolerance, native actinomycetes isolates of Streptomyces spinoverrucosus (MNT-7), Streptomyces spp. (PTK-4) and Streptomyces cellulosae (VER-4) evaluated under pot culture. MNT-7 (Streptomyces spinoverrucosus) significantly increased all the growth parameters and yield also recorded the minimum sheath blight percent disease incidence of 6.79 under pot culture studies. The present study revealed that Streptomyces spinoverrucosus (MNT-7) was the most promising PGPR for plant growth promotion and sheath blight disease management. To, the best of knowledge, Streptomyces spinoverrucosus is the first report of PGPR tolerant to drought and acidic pH. However, further evaluation field is needed to confirm the findings.Item Plant growth promoting actinobacteria from rhizosphere soils of Black pepper in Wayanad(Department of Agricultural Microbiology, College of Agriculture, Vellanikkara, 2021) Rineesha Backer, A; Girija, DBlack pepper (Piper nigrum L.) known as the ‘King of spices’ is one of the important export-oriented spice crops that provides major source of income and employment for rural households in Kerala. Wayanad is one of the main pepper growing tracts in Kerala. However, the production of black pepper in Wayanad has been declining over the past many years, mainly due to the poor soil health status, improper land management and changes in climatic factors. An increasing demand for low-input agriculture has resulted in a greater interest in soil microorganisms which are able to enhance plant health and soil quality. However, actinobacteria have not yet been exploited for this purpose. Hence the present study focused on isolation, screening and characterization of actinobacteria from rhizosphere soils of black pepper in Wayanad and evaluation of their plant growth promoting activity. Rhizosphere soil samples were collected from five different locations of flood affected and non-flood affected black pepper growing areas of Wayanad district. Enumeration of actinobacteria on three different media revealed that the population of actinobacteria ranged from 1.00 x104 cfu to 12.00 x104 cfu g -1 soil in non-flooded soil. Actinobacteria could not be detected in flooded soils, even at a dilution of 10-1 , except in Meppadi. Among the different media, starch casein agar recorded higher population of actinobacteria. A total of 35 isolates were purified and maintained for characterization and screening for plant growth promoting activities. Cultural, morphological and biochemical characters of all 35 isolates of actinobacteria were studied. All the isolates were Gram positive, and they varied in the colony morphology, colour of aerial mycelium, spore chain morphology and pigmentation. Two isolates Vlt-K and Plp-B produced yellow water-soluble pigment and Vlt-I produce purple water insoluble pigment. Screening of all the 35 isolates under in vitro conditions for plant growth promoting (PGP) activities revealed that the isolates were highly variable. Two isolates (Ptd-A and Amb-C) were superior to other isolates in IAA production. Significantly higher N-fixation was noticed in four isolates (Ptd-A, Ptd-E, Ptd-B and Ptr-A). Six isolates solubilized insoluble phosphate to available P, and also reduced the pH of the medium. Reduction in pH by phosphate solubilizers has been reported earlier and this is attributed to the production of organic and inorganic acids. None of the isolates solubilized K or Zn. Three isolates with multiple PGP activities were selected, based on ranking for PGP activities in vitro and identified by 16S rRNA gene sequencing (Ptd-A and Ptr-A as Streptomyces sp. and Ptd-E as Actinobacteria bacterium). These actinobacterial isolates evaluated in-planta for PGP activities with black pepper cuttings (variety Panniyur-1). Treatments also included PGPR mix-1 (KAU commercial formulation) and Organic Package of Practices Recommendations (2017). All the three native isolates exhibited significant increase in shoot length, number of leaves and internode length throughout the growth period from planting to five months. Significantly higher root growth was observed in treatment T2: Ptd-A (Streptomyces sp.), with significantly higher root volume, fresh and dry root weight. Significantly higher plant fresh weight was observed in T2: Ptd-A (Streptomyces sp.) and significantly higher plant dry weight was observed in T2: Ptd-A (Streptomyces sp.) and T3: Ptr-A (Streptomyces sp). The present investigation revealed that native actinobacteria have the potential to improve the growth of black pepper. These isolates may further be evaluated under field conditions before commercialization. Screening for other beneficial traits like disease suppression and drought tolerance may also be carried out. The compatibility of the actinobacteria with other PGP microorganisms may also be evaluated. Actinobacterial spores survive in soil for longer periods and this may be an added advantage. Actinobacterial diversity and the biochemical molecules produced by actinobacteria could be exploited to build up sustainable and eco-friendly agriculture.Item Exopolysaccharide producing bacteria from soil based nesting structures of insects(Department of Agricultural Microbiology, College of Agriculture, Vellayani, 2022) Sruthi Suresh; Chitra, NThe study entitled ―Exoploysaccharide producing bacteria from soil based nesting structures of insects‖ was conducted during the year 2019-2021 in the Department of Agricultural Microbiology, College of Agriculture, Vellayani, Thiruvananthapuram with the objective to isolate and characterize exopolysaccharide producing bacteria from mud wasp and termitaria and the ability of the best two isolates in soil aggregate stability study. Thirty three bacterial isolates were obtained from different termitaria and mud dauber wasp nest. Among them colonies of fifteen isolates had slimy mucoidal appearance and were identified as exopolysaccharide producers. The exopolysaccharide production of the isolates ranged from 25.78 µg mL-1 (Klebsiella pneumoniae KWP23) to 2.58 µg mL-1 . The total carbohydrate content in exopolysaccharide was maximum in bacterial isolate Paenibacillus polymyxa KTM17 (14.48 µg mL-1 ). The best five isolates were selected for molecular characterization by 16s rRNA sequencing and identified as Priestia aryabhattai TWP12, Priestia aryabhattai TWP13, Klebsiella pneumoniae KWP23, Priestia megaterium KTM4, Paenibacillus polymyxa KTM17. They were screened for phosphate, potassium and silicate solubilization. Klebsiella pneumoniae KWP23 showed solubilization zone for phosphate (4 mm) and potassium (1 mm). None of the isolates chosen were silicate solubilizers. Two bacterial isolates with maximum EPS production viz. Paenibacillus polymyxa KTM17 and Klebsiella pneumoniae KWP23 were selected for the further studies. Effect of carbon source and carbon: nitrogen ratio on exopolysaccharide production was studied. Glucose was found to be the best carbon source for EPS production in Klebsiella pneumoniae KWP23 at C: N ratio of 10:1. In Paenibacillus polymyxa KTM17, highest EPS production was recorded when sucrose was used as carbon source at a C: N ratio of 50:1. The effect of temperature on EPS production of the isolates was evaluated. Increase in incubation temperature resulted in a corresponding increase in EPS production in case of Klebsiella pneumoniae KWP23. The highest EPS 3 production by Klebsiella pneumoniae KWP23 was (23.00 µg mL-1 ) at 50oC and Paenibacillus polymyxa KTM17 at 30oC (31.50 µg mL-1 ). The effect of salinity on EPS production by Klebsiella pneumoniae KWP23 and Paenibacillus polymyxa KTM17 isolates was also assessed. For Klebsiella pneumoniae KWP23, the EPS production was maximum without NaCl (18.0 µg mL-1 ) and for Paenibacillus polymyxa KTM17, the EPS production was maximum at 6% (1 M) NaCl (26.25 µg mL-1 ). Klebsiella pneumoniae KWP23 and Paenibacillus polymyxa KTM17 were further subjected to dual culture plate assay to study the biocontrol potential of the isolates. Paenibacillus polymyxa KTM17 showed a clear inhibition zone on dual culture assay with Rhizoctonia solani, but Klebsiella pneumoniae KWP23 did not inhibit the growth of the fungus. Both Klebsiella pneumoniae KWP23 and Paenibacillus polymyxa KTM17 inhibited the growth of Helminthosporium sp. The potential of the isolates to form soil aggregates and its aggregate stability was studied. The mean weight diameter of dry aggregates obtained was highest for the soil amended with Paenibacillus polymyxa KTM17 (1.068 mm). The study on wet aggregate stability on water immersed revealed that the best soil aggregate stability was given by the isolate Paenibacillus polymyxa KTM17. The stability of the aggregate lasted for more than 24 hours when immersed in water whereas that in the aggregate kept as control disintegrated immediately on pouring water. The effect of agitation and water immersion on the aggregate stability was also analyzed. On oscillation of the aggregates in water the aggregates in control soil showed maximum turbidity (0.254 nm). The dry weight of the disintegrated soil was minimum in the soil aggregate amended with Paenibacillus polymyxa KTM17 (0.014 g). Based on the results of the present study, it can be concluded that among the selected isolates Klebsiella pneumoniae KWP23 had maximum production of EPS. Both Klebsiella pneumoniae KWP23 and Paenibacillus polymyxa KTM17 has biocontrol potential against plant pathogenic fungi. Paenibacillus polymyxa KTM17 is a potential isolate which can effect soil aggregate stability in dry and wet condition.