RESUMEN

Plant probiotic mechanisms of endophytic microorganisms are highly remarkable as it play key role in growth and health of plants. Even though Burkholderia spp. have been studied for their role in plant growth and disease management, report on their field performance is very limited. Hence, the objective of the study was to investigate the plant probiotic performance of selected Burkholderia spp. on Capsicum frutescens. The results of the study showed bacterial influence on growth of C. frutescens with remarkable induction of early flowering and fruiting. Most interestingly, the plants treated with Burkholderia strains, ZoB74 and ZoB82 were found to have limited infestation with Bemisia tabaci. However, the control plants and those treated with Burkholderia ZoB86 were observed to have stunted growth with crumpled and curled leaves with no flowers or fruits. Hence, the study confirmed the strain specific potential of Burkholderia spp. in triggering the early flowering and fruiting in C. frutescens with associated protection from insect attack.

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Endophytic microorganisms play a significant role in plants response to beneficial organisms and pathogens. In the current study, endophytic microorganisms from Zingiber officinale were screened for in vitro inhibition against Pythium myriotylum. From this, Burkholderia vietnamiensis ZoB74 was selected as an organism with remarkable antifungal effect. Further, the study focussed on analysis of in vivo changes in endophytic bacterial community of Z. officinale in presence of selected organisms and the pathogen P. myriotylum by PCR-DGGE. 16S rDNA sequencing of bacterial community after DGGE has resulted in the identification of a group of uncultured bacteria as the predominant microbial community of rhizome under various conditions of treatment. High frequency dominance of these endophytic bacteria suggests their role in disease resistance to soft rot in ginger. This also revealed the variation of endophytic microbiome of Z. officinale under biotic stress. Hence the study provides molecular insight into uncultured microbiome and its stress-inducible variation in ginger rhizome.

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Novel and potential antimicrobial compounds are essential to tackle the frequently emerging multidrug-resistant pathogens and also to develop environment friendly agricultural practices. In the current study, endophytic actinomycetes from rhizome of Zingiber officinale were explored in terms of its diversity and bioactive properties. Fourteen different organisms were isolated, identified and screened for activity against Pythium myriotylum and human clinical pathogens. Among these, Nocardiopsis sp. ZoA1 was found to have highest inhibition with excellent antibacterial effects compared to standard antibiotics. Remarkable antibiofilm property was also shown by the extract of ZoA1. Its antifungal activity against Pythium and other common phytopathogens was also found to be promising as confirmed by scanning electron microscopic analysis. By PCR-based sequence analysis of phz E gene, the organism was confirmed for the genetic basis of phenazine biosynthesis. Further GC-MS analysis of Nocardiopsis sp. revealed the presence of various compounds including Phenol, 2,4-bis (1,1-dimethylethyl) and trans cinnamic acid which can have significant role in the observed result. The current study is the first report on endophytic Nocardiopsis sp. from ginger with promising applications. In vivo treatment of Nocardiopsis sp. on ginger rhizome has revealed its inhibition towards the colonization of P. myriotylum which makes the study to have promises to manage the severe diseases in ginger like rhizome rot.

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Plants are ubiquitously colonized by endophytic microorganisms which contribute significantly to plant health through production of plant growth regulators or disease suppression. In the present study, an endophytic bacterial isolate designated as BmB 1 with significant antifungal and plant growth promoting properties was isolated from the stem tissue of Bacopa monnieri (L.) Pennell. The isolate was studied in detail for the molecular and chemical basis of its bioactivity which proved it to have the presence of surfactin, iturin, and type I polyketide synthase (PKS) genes. For the analysis of the chemical basis of antifungal property, extract of the isolate was initially checked for its activity on test pathogens and LC-MS/MS based analysis further confirmed the presence of bacillomycin (m/z (M+H(+)) 1031.8) and surfactin (m/z (M+H(+)) 1008.6 and 1022.6) in the extract prepared. The light microscopic and SEM analysis of the treated and untreated mycelia of the pathogens clearly revealed the hypal destruction caused by the compounds produced by the selected isolate. This confirms the ability of the organism to directly inhibit the growth of the tested pathogens. The GC-MS analysis also confirmed the isolate to have the presence of volatile compounds with the expected role to induce induced systemic resistance (ISR) of the plant. Because of the multitargeted antifungal property, the isolate which was identified as Bacillus amyloliquefaciens can have potential biocontrol applications.

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