New report of root endophyte - Enterobacter cloacae having in vitro growth promoting attributes and biocontrol potential against Curvularia lunata causing leaf spot disease of banana

Abstract

The Banana plant (Musa paradisiaca) worldwide cultivated crop harbors many endophytic bacteria. Endophytic bacteria are those that live inside plant tissues without producing visible symptoms of infection or having an adverse effect on their hosts. Root samples were collected from different fields of banana (Musa paradisiaca) of the District Uttar Dinajpur. GPS locations of the banana fields were also taken by using mobile GPS location application.Bacterium-MRH-6 was isolated from root pieces. The scanning electron microscopic image of bacterial isolate (MRH 6) was taken. 16S rDNA fragment sequence was found to be Enterobacter cloacae and was deposited to GenBank with accession number ON955844. E. cloacae showed plant growth promoting (PGP) traits like IAA production, phosphate solubilization. The bacterium showed phosphate-solubilising activity by producing a clear zone on the Pikovskaya’s (PKV) medium. E. cloacae was positive in IAA production and catalase production. For quantification, HPLC analysis of IAA from culture filtrate of E. cloacae was done by injecting 10μl of the filtered extract onto a (C18, 5μm 25×0.46 cm, Make: Agilent, Model: Infinity 1260) in a chromatograph equipped with a differential ultraviolet detector absorbing at 254 nm. Mobile phase was acetonitrile 60% and Water 40% and flow rate 1.0ml/min. Retention times for peaks were compared to IAA standard and quantified. E. cloacae recorded IAA production of (3.509 × 20)-70.18 ng/μl. The bacterium showed sensitivity to antibiotic chloramphenicol (30μg) and resistant to ampicillin (10μg). The leaf spot disease in banana from Sarai Raiganj was first reported by Chowhan and Chakraborty (2022) and Koch’s postulate was successfully established for the pathogen causing leaf spot disease in banana. 18S rDNA fragment sequence of strain MLP-01 was deposited on GenBank with accession number ON246070. The fungus was morphologically identified as Curvularia lunata by Agharkar Research Institute, Pune, India with Accession number NFCCI 5361. E. cloacae showed in vitro antagonism against C. lunata (ON246070). E. cloacae also checked the growth of the tested pathogen significantly. The tested fungus was inhibited to some degree, the percentage inhibition was 75% by E. cloacae.