Phytohormone production endowed with antagonistic potential and plant growth promoting abilities of culturable endophytic bacteria isolated from Clerodendrum colebrookianum Walp.

In this study, culturable endophytic bacterial isolates obtained from an ethnomedicinal plant Clerodendrum colebrookianum Walp., were assessed for their diversity, in vitro screening for their plant growth promoting (PGP) activities and to use them as inoculant for in vivo PGP activities with biocontrol potential. Totally, 73 isolates were recovered from different tissues of C. colebrookianum were identified by 16S rRNA gene sequencing and phylogenetically analyzed by using BOX-PCR fingerprinting. Out of 73 isolates, 52 exhibited varying extents of antagonistic potential were selected for screening for various PGP traits. Concerning the PGP activities, the percentage of isolates positive for P-solubilisation, indolic compounds production, siderophore and ammonia production were 84.6, 92.3, 78.8 and 98.0 respectively. All isolates were positive for the production of hydrocyanic acid (HCN) and 86.5%, 84.6% and 90.3% of isolates showed significant cellulase, amylase and protease production respectively. Further, the top 10 bacterial isolates based on a bonitur scale with multiple PGP activities were screened for root surface colonization and biofilm formation ability. Out of selected 10 isolates, 9 showed significant potential for root surface colonization on tomato roots. Isolate BPSAC6 identified as Bacillus sp. was most efficient in biofilm formation as assessed with respect to the intensity of crystal violet, which further showed their potential to withstand various biotic and abiotic stresses. Furthermore, Bacillus sp. strain BPSAC6 showed a significant increase in shoot and root height as well as fresh weight after 45 and 60 d of inoculation with tomato seedlings. Additionally, biosynthetic potential of antagonistic isolate was detection by using PKSI, PKSII and NRPS biosynthetic genes. Two isolates Pseudomonas psychrotolerans and Labrys wisconsinensis were reported first time as an endophyte. At last, first time an endophytic bacterial strain Bacillus sp. BPSAC6 was reported to produce altogether three phytohormones (IAA, Kinetin and 6-Benzyladenine). This study is the first report that bacteria isolated from C. colebrookianum has biocontrol as well as PGP abilities endowed with phytohormones production and can be used for the preparation of bioinoculant for plant growth promotion.

Passari AK ，Mishra VK ，Leo VV ，Gupta VK ，Singh BP ... -  《-》

Detection of biosynthetic gene and phytohormone production by endophytic actinobacteria associated with Solanum lycopersicum and their plant-growth-promoting effect.

In the present study, fifteen endophytic actinobacterial isolates recovered from Solanum lycopersicum were studied for their antagonistic potential and plant-growth-promoting (PGP) traits. Among them, eight isolates showed significant antagonistic and PGP traits, identified by amplification of the 16S rRNA gene. Isolate number DBT204, identified as Streptomyces sp., showed multiple PGP traits tested in planta and improved a range of growth parameters in seedlings of chili (Capsicum annuum L.) and tomato (S. lycopersicum L.). Further, genes of indole acetic acid (iaaM) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase (acdS) were successively amplified from five strains. Six antibiotics (trimethoprim, fluconazole, chloramphenicol, nalidixic acid, rifampicin and streptomycin) and two phytohormones [indole acetic acid (IAA) and kinetin (KI)] were detected and quantified in Streptomyces sp. strain DBT204 using UPLC-ESI-MS/MS. The study indicates the potential of these PGP strains for production of phytohormones and shows the presence of biosynthetic genes responsible for production of secondary metabolites. It is the first report showing production of phytohormones (IAA and KI) by endophytic actinobacteria having PGP and biosynthetic potential. We propose Streptomyces sp. strain DBT204 for inoculums production and development of biofertilizers for enhancing growth of chili and tomato seedlings.

Passari AK ，Chandra P ，Zothanpuia ，Mishra VK ，Leo VV ，Gupta VK ，Kumar B ，Singh BP ... -  《-》

Endophytes from Gnetum gnemon L. can protect seedlings against the infection of phytopathogenic bacterium Ralstonia solanacearum as well as promote plant growth in tomato.

Endophytes are beneficial plant microbes which help the plants by producing various plant growth promoting substances and also by acting as biocontrol agents against various plant pathogens. In the present study, evaluation of endophytic bacteria isolated from Gnetum gnemon, an ethnomedicinal plant was carried out for their plant growth promoting (PGP) activity and antagonistic potential against bacterial wilt pathogen Ralstonia solanacearum. Initially a total of 40 endophytic bacteria were isolated which were clustered into 13 groups based on RFLP and BOX-PCR fingerprinting. These 13 representative isolates belonged to different genera of Bacillus (9), Solibacillus (1), Staphylococcus (2) and Caballeronia (1). Among them, six isolates were positive for production of IAA, the value of which ranged from 11.16 to 27.63 μg mL-1. Phosphate solubilisation in the range of 106.4 to -212.7 μg mL-1 was shown by three isolates. Eight isolates producedammonia, the value of which ranged from 1.3 to 6.1 μmol mL-1. All tested isolates were positive for siderophore production. For extracellular enzyme production, 7 isolates were positive for protease, 8 for cellulase and 10 for amylase production. The isolates were also tested for their antagonistic activity against R. solanacearum in vitro and in planta assay using tomato seedlings. Staphylococcus warneri GL1 showed the highest biocontrol efficacy of 77.67 % followed by Bacillus velezensis GL3 i.e. 70.1 %. R. solanacearum antagonistic isolates were analysed for the presence of antimicrobial peptide biosynthesis genes bmyB, srfAA, fenD and ituC. All the antagonistic isolates showed the presence of all four genes, except the isolate Bacillus velezensis GMC2, where the gene for fengycin synthetase (fenD) was absent. Based on in vitro PGP traits, three isolates Bacillus velezensis GL3, Bacillus atrophaeus GMC1 and Bacillus megaterium GS2 were selected, these three endophytic bacteria individually and their consortia were tested for in planta PGP activities in tomato plants. Application of Bacillus velezensis GL3 alone and consortia of three isolates showed significant improvement in growth parameters such as shoot length, fresh weight and dry weight in a pot experiment. Colonization of endosphere of treated tomato seedlings by the endophytic isolate Bacillus velezensis GL3 was confirmed by visualization of colony morphology and BOX-PCR fingerprinting. Our study highlights the potential of endophytes associated with unexplored plants like G. gnemon for development of bioformulation aimed at enhancing plant growth and bacterial wilt disease control.

Agarwal H ，Dowarah B ，Baruah PM ，Bordoloi KS ，Krishnatreya DB ，Agarwala N ... -  《-》

Growth stage and tissue specific colonization of endophytic bacteria having plant growth promoting traits in hybrid and composite maize (Zea mays L.).

Maize, a crop cultivated worldwide, was investigated for plant tissue and crop stage specific colonization of endophytic bacteria. Such bacterial interactions have high potential to enhance maize grain yield by means of biological nitrogen fixation and/or plant growth promoting activities. In this study endophytic bacteria were isolated from a hybrid PEEHM-5 and composite PC-4 maize varieties using root, stem and leaf tissues of plants at vegetative, flowering and maturity stages of growth. PEEHM-5 harbored higher endophytic bacterial population than PC-4 at all growth stages, with highest in roots and at flowering stage. Morphologically 188 different endophytic isolates (82 from PEEHM-5, 106 from PC-4) were screened for plant growth promoting attributes viz. P, K, Zn solubilization, production of hormones, siderophore, ACC deaminase, HCN, biological nitrogen fixation and biocontrol of two maize fungal pathogens. Thirty one potential PGP isolates on RFLP analysis of their amplified 16S rRNA gene, were clustered in 13 phylogenetic groups. On sequencing and blasting of amplified 16S rRNA gene of representative isolates from each group identified PC-4 endophytic bacterial isolates as Bacillus aryabhattai, Pantoea cypripedii, Bacillus licheniformis, Klebsiella sp., Pantoea dispersa, Klebsiella variicola, Pantoea sp., Agrobacterium larrymoorei and PEEHM-5 endophytic bacterial isolates as Bacillus sp., Bacillus amyloliquefaciens, Lactococcus lactis, Bacillus cereus and Staphylococcus hominis. In planta evaluation of potential isolates at variable chemical fertilizer input indicated their potential in compensating nearly 25% of the fertilizer input as observed on their improvement of shoot and root parameters. Lactococcus lactis inoculation influenced maximum followed by Pantoea and Klebsiella isolates.

Marag PS ，Suman A 《-》

Biocontrol and plant growth-promoting ability of plant-associated bacteria from tomato (Lycopersicum esculentum) under field condition.

Forty-five bacterial isolates recovered from surface-sterilized root, stem and leaf tissues of tomato were studied for their antifungal activity against phytopathogens, and plant growth-promoting (PGP) and biocontrol traits. Six plant-associated bacteria suppressed all the pathogens tested under in vitro plate assay and also shown PGP and biocontrol traits. The six isolates showing PGP and biocontrol properties were identified as Bacillus spp., based on the microbial identification system (Biolog) and partial sequence analysis of 16S rDNA. Two independent field trials were conducted with biocontrol bacteria along with chemical control (Thiram+Fytolan) and control (Without treatment). The averaged results of two field trails revealed that tomato plants inoculated with BETS11 (11.73 t/ha) and BETR11 (11.24 t/ha) strains showed significantly higher yield and disease reduction on par with chemical control (11.81 t/ha). However, there was an increase in the yield with respect to uninoculated control except the isolate BETS5 (9.09 t/ha). Therefore, the isolates BETS11 and BETR11 may be used as efficient biofertilizer and bio-control agent for tomato production in the Island agricultural ecosystem.

Amaresan N ，Jayakumar V ，Kumar K ，Thajuddin N ... -  《-》