Study area and collection of samples
Fresh and healthy leaves, twigs, roots and barks of P. napaulensis were collected from Shangpung (Lat. 25.47816°, Long. 92.35328°) West Jaintia Hills, Meghalaya, India. The samples were transferred in sterilized plastic zip bags and brought to laboratory to carry out further studies.

Isolation of fungal endophytes and maintenance of pure culture
The plant samples (leaves, twigs, roots and barks) were washed clean with running water in order to remove any unwanted entities which might have adhered to the surface of the samples. Surface sterilization was done by subjecting the plant samples to 70% ethanol (Analytical AR Grade Ethanol Absolute) for 2-3 minutes, followed by 1% sodium hypochlorite (HiMedia) for 1-2 minutes and 2-3 times washing with sterile distilled water.¹³ About 1 cm of the explants were cut from the sterilized samples, air dried and inoculated in potato dextrose agar (HiMedia) plates containing 100 mg/L of streptomycin sulphate (HiMedia). The plates were incubated for 10 days at 28 ± 2 °C and the pure cultures for the obtained endophytic fungal isolates were maintained following the same procedure.¹⁴

Identification of fungal endophytes
The isolated fungal endophytes were identified morphologically and microscopically based on their vegetative and reproductive structures using standard manuals.^15,16 For molecular characterization the fungal isolates were cultured in potato dextrose broth (HiMedia) for 10 days and were then used for identification by adapting the procedures given by National Bureau of Agriculturally Important Microorganisms (NBAIM) by analysing the Internal transcribed Spacer (ITS) region. The amplification of locus analysed (ITS) was performed using universal primers for the ITS region, ITS 1 and ITS 4.¹⁷ The obtained PCR products were purified and sequenced at Eurofins Genomics India Pvt. Ltd., Bengaluru, Karnataka, India. Analysis of the sequences were carried out using BLAST program from GenBank database (NCBI), sequence with highest similarity was downloaded. Sequences were aligned using MEGA 11 software and using Clustal W alignment program. The resulting sequences were deposited to the GenBank database and the accession numbers were acquired.

Analysis of enzymatic assay
Amylase test
Qualitative analysis for amylase was done by inoculating isolates in starch agar (HiMedia) plates and incubated at 28 ± 2 °C for 10 days. Following incubation, the plates were flooded with 0.5% iodine solution for a minute. Occurrence of clear zones around the colonies depicted positivity for amylase production.¹⁸ Quantification of amylase was done by using the filtrates of 10 days old fungal broth grown in potato dextrose broth (PDB) containing 1% starch. A reaction mixture comprising of 1 ml of filtrate (enzyme broth) and 0.5 ml of soluble starch (1%) was incubated for 30 minutes at 37 °C and then 0.5 ml Dinitrosalicylic acid (DNS) was added. The solution was diluted to 5 ml by adding distilled water. The optical density (OD) of the developed reddish brown colour was recorded at 540 nm using UV/Vis Spectrophotometer (Lambda 35, Perkin Elmer, USA). Readings were taken in triplicate and quantity of sugar produced was read off by considering the standard curve of maltose. The result was expressed in unit per ml (Uml^-1), where one unit of amylase is the amount of enzyme releasing a µmol of reducing sugar, expressed as maltose, per min, per ml, under given condition.¹⁹

Cellulase test
Qualitative analysis for cellulase was determined by inoculating fungal isolates in PDA plates amended with 1% carboxymethylcellulose (CMC) and incubating for 10 days at 28 ± 2 °C. Following incubation, plates were flooded with congo red solution (0.1%) for 15 minutes, the excess stain was washed with 1M NaCl solution for 10 minutes.²⁰ Occurrence of clear zones around the colonies indicated positive activity for cellulase. Quantification of Endo-β-1,4-glucanase (Carboxymethyl cellulase) was done by centrifuging 10 days grown PDB cultures of endophytic fungi at 10,000 rpm (Eppendorf, Centrifuge 5430 R) for 15 minutes. The reaction mixture comprised of 1 ml supernatant and 1 ml of 1% CMC in 0.05 M sodium citrate buffer with pH 4.8. The mixture was incubated at 50 °C for an hour and the 3 ml of alkaline DNS reagent was added to halt the reaction. Absorbance was measured at 540 nm and readings were taken in triplicates. The result was expressed in Unit per ml (Uml^-1), where one unit of enzyme (CMC-ase) is the amount of enzyme releasing a µmol of reducing sugars, expressed as glucose, per min, per ml, under given condition.¹⁹

Protease test
Protease activity was screened by inoculating fungal isolates in skim milk agar plates followed by incubating for 10 days at 28 ± 2 °C.²¹ Occurrence of clear zones around the colonies specified positive activity of protease. Protease quantification was done by centrifuging the fungal cultures grown in PDB amended with 1% casein (10 days) at 10,000 rpm (using Eppendorf, Centrifuge 5430R) for 15 minutes. The reaction mixture comprised of 1 ml of the supernatant and 5 ml of 0.5 N NaOH. The mixture was mixed vortex and 1.5 ml of Folin-Ciocalteu reagent (diluted to 1:1 v/v) was added and incubated for 30 minutes in the dark at room temperature. Development of blue colour indicated protease activity and absorbance was measured at 660 nm using tyrosine standard. The result was expressed in unit per ml (Uml^-1), where one unit of protease is the amount of enzyme releasing µmol of tyrosine per ml per min under the given condition.²²

Catalase test
Catalase activity was determined by mixing small inoculum of the isolates with 3% hydrogen peroxide solution. Intensity of bubble evolution indicated the catalase producing potential of the fungi: (-) no activity, (+) low activity, i.e. few bubbles, (++) moderate activity, (+++) high activity, i.e. abundant bubbles.²³

Hydrogen cyanide (HCN) production test
Production of HCN was detected by inoculating isolates onto PDA plates. The media used for the test contained 0.4% L-Glycine. Thin Whatman filter paper strips were soaked in a solution of 2% Na₂CO₃ and 0.5% picrate. Single strips were adhered to the lids of petri dish and secured using parafilm. The plates were incubated for 10 days at 28 ± 2 °C. Any alteration in the strips colour after the incubation period indicated the evolution of HCN.²⁴

Urease test
Urease test was done by inoculating fungal isolates in plates containing Christensen’s urea agar (HiMedia) and incubating for 10 days at 28 ± 2 °C. Change in the colour medium denoted the urease activity: no change in colour implies negative (-), orange colour means weak activity (+), pink colour means moderate activity (++) and red colour means strong activity (+++).²³

Isolation, identification and culture of fungal phytopathogens
Fungal phytopathogens were isolated from diseased parts of Sechium edule (leaf), Solanum tuberosum (leaf) and Mangifera indica (fruit pericarp and leaf), and identified following the methods as described above for the endophytic fungi.

Assessment of antagonistic potential of endophytic fungi in in vitro condition
The in vitro assessment of antagonistic potential of the isolated endophytic fungi was carried out by dual culture technique. A 6 mm mycelial disc of fungal pathogens and fungal endophytes obtained from 4 days old cultures were placed opposite to each other on PDA plates, secured with parafilm and incubated for 10 days at 28 ± 2 °C.²⁵ Percentage of growth inhibition was determined using the formula:

Growth Inhibition % = R1-R2 / R1 × 100

Where, R1 indicates the radial growth of the pathogen’s control colony and R2 indicates the radial growth of the pathogen in a treated colony.

Determination of the zone of interaction between the fungal endophytes and pathogens’ colonies
The interaction zone between the fungal endophytes and pathogens in dual culture were studied using Scanning Electron Microscopy (SEM) in Sophisticated Analytical Instrument Facility, North-Eastern Hill University, Shillong, India. Samples were prepared based on the method given by NEHU-SAIF. Mycelial cubes of 0.5 cm were cut using sterilized blade at the interaction zone in a dual culture plate. The samples were fixed with 3% Glutaraldehyde for 2 hours and then immersed in 0.1 M Sodium Cacodylate buffer for 15 minutes at 4 °C to wash off the excess fixative (3 changes for 15 minutes each). The samples were then subjected to gradient dehydration using acetone (30%-100%) and followed by immersion in Tetramethylsilane for 10-15 minutes at 4 °C. The samples were oven dried at 26 °C to remove the moisture. The dried samples were mounted on SEM stubs, gold sputter coated and observed under SEM (JEOL JSM-6360 SEM) at 20 kV.

Data analysis
The data analysis (analysis of variance and Tukey’s HSD test at P ≤ 0.05) were done using SPSS, v.25 (Chicago, IL, USA). Evaluation of various extracellular enzymatic activities and antagonistic potential of the isolated endophytic fungi were done in triplicates.