Novel free living diazotrophs associated with black pepper in Wayanad

K. M. Fathima Shaheena, D. Girija, K. Surendra Gopal, P. Sureshkumar, P. G. Sadhan Kumar


Diazotrophs are nitrogen fixing microorganisms that play a key role in maintaining soil health by converting atmospheric nitrogen into plant available form through biological nitrogen fixation (BNF). In this study, free living diazotrophic bacteria were isolated from rhizosphere soil and phylloplane of black pepper from Wayanad. Twenty predominant isolates were screened for growth and nitrogen fixation at varying levels of pH. There was a decrease in growth and N-fixation, when the pH was reduced from seven to five. Many of the isolates exhibited plant growth promoting (PGP) traits like production of indole acetic acid (IAA), ammonia and hydrogen cyanide (HCN) under in vitro conditions. A few isolates were found to possess antagonistic activity against the soil borne plant pathogens, Rhizoctonia solani and Ralstonia solanacearum. However, none of the isolates exhibited antagonistic activity against the pathogen, Fusarium oxysporum. Based on in vitro screening, four isolates were found to be promising diazotrophs, and these were identified by 16S rDNA sequencing as Microbacterium (NKdS and NPPV), Cellulosimicrobium (NPS-1) and Brevundimonas (NKPV-2), Microbacterium is an actinomycete, reported to be endophytic in certain crop species. Nitrogen fixation combined with other plant growth promoting activities makes them an attractive choice for further exploitation as biofertilizers.


Acid tolerance, Free living diazotrophs, PGP activities.

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A KAU publication [CODEN: JTAGEI; ISSN 0971-636X; eISSN 0973-5399]