Isolation and Identification of Shoot-Tip Associated Endophytic Bacteria from Banana cv. Grand Naine and Testing for Antagonistic Activity against <i>Fusarium oxysporum</i> f. sp. <i>cubense</i>

Abstract

Endophytic bacteria colonizing the shoot-tips of banana cv. Grand Naine were isolated and tested for the antagonistic activity against the Panama wilt pathogen <i> Fusarium oxysporum </i> f. sp. <i> cubense </i> (Foc). Pre-isolation, the suckers were given extensive disinfection treatments and the homogenate from the excised shoot-tip portion was plated on nutrient agar (NA) and trypticase soy agar (TSA). This yielded altogether 47 isolates: 26 on NA and 21 on TSA, respectively, from the 10 suckers collected during August to February. The number of bacterial isolates obtained per sucker varied from one to 15 based on colony characteristics registering up to 10 distinct species per shoot-tip based on 16S rRNA sequence analysis. The 47 isolates belonged to 19 genera and 25 species under the phylogenetic classes of Actinobacteria, α- and γ-Proteobacteria and Firmicutes. Actinobacteria constituted the predominant phylum (55% isolates) with the constituent genera of <i> Arthrobacter, Brevibacterium, Corynebacterium, Curtobacterium, Kocuria, Kytococcus, Micrococcus, Naumanella, Rothia </i> and <i> Tessaracoccus </i> spp. and an unidentified isolate belonging to the family Frankiaceae. Proteobacteria constituted the second major phylum ( <i> Brevundimonas, Enterobacter, Klebsiella, Pseudomonas, Serratia </i> and <i> Sphingomonas </i> spp.) followed by Firmicutes ( <i> Bacillus </i> and <i> Staphylococcus </i> spp.). Antagonistic activity of the endophytes against Foc was tested through agar plate assays (pit and spot applications on fungal lawn) employing potato dextrose agar and NA. Endophytic <i> Pseudomonas aeruginosa </i> (isolate GNS.13.2a) which was associated with a single sucker showed significant growth inhibition effect on Foc while <i> Klebsiella variicola </i> (GNS.13.3a) and <i> Enterobacter cloacae </i> (GNS13.4a) exhibited moderate inhibition. The study brings out considerable sucker to sucker variation in the associated cultivable endophytic bacteria in “Grand Naine” banana and identifies a few bacterial endophytes with biocontrol potential against the devastating Foc pathogen.