Dynamic mangrove ecosystems are fascinating sources of microorganisms which serve as an extraordinary habitat for the growth and development of many endophytic microorganisms. In this study, we isolated 16 endophytic fungi thriving in the mangrove species Bruguiera cylindrica, collected from Ayiramthengu in the state of Kerala, India. All the isolated endophytes were screened for their plant growth promoting activities (IAA, siderophore and HCN production, ACC deaminase activity) and enzyme production. Among the isolates, seven displayed only a single trait from the total plant growth promoting traits evaluated, although IAA production was a common trait observed amongst the lot. When IAA concentration was quantified in the culture medium, the isolate MEF 21 showed the highest IAA production (>45 µg/mL). The ability of MEF 21 isolate to produce IAA, both in the presence and absence of L-Tryptophan was confirmed by TLC and GC-MS analysis. The isolate also produced siderophores and displayed ACC deaminase activity. The fungus exhibited high extracellular enzyme activity such as amylase, cellulase and protease. Vigna radiata seeds were treated with culture filtrates of MEF 21 to determine its plant growth promoting ability by vigor index method. A germination percentage of 93% and a vigor index of 337.59 were displayed by MEF 21 alone. In vitro antagonistic activity was also exhibited by MEF 21 against the plant pathogen Xanthomonas campestris with a growth inhibition zone of 35 ± 1.5 mm diameter in the dual culture plate. This efficient plant growth promoting isolate, MEF 21, was further identified using morphological, biochemical and phylogenetic methods. Molecular identification included ITS-PCR utilizing universal primers. The PCR products were sequenced and submitted to GenBank. The isolate thus identified was Geotrichum candidum with an accession number JX 477426. These findings revealed the efficacy of the endophytic yeast, isolated from the surface sterilized root of the mangrove plant, to promote plant growth, development and protection.

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