Plant growth-promoting traits of Pseudomonas geniculata isolated from chickpea nodules

Subramaniam Gopalakrishnan 0 Vadlamudi Srinivas 0 Bandikinda Prakash 0 Arumugam Sathya 0 Rajendran Vijayabharathi 0 0 S. Gopalakrishnan (&) V. Srinivas B. Prakash A. Sathya R. Vijayabharathi International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) , Patancheru 502 324, Telangana , India A bacterium, isolated from nodules of chickpea grown in alluvial soils of Haryana state of India, designated as IC-76 was characterized for in vitro plant growth-promoting (PGP) properties and further evaluated under greenhouse, on-station and on-farm field conditions for PGP activity in chickpea. The isolate IC-76 produced indole acetic acid, siderophore, hydrocyanic acid, cellulase, protease, and b-1,3-glucanase. When the bacterium was evaluated individually for their PGP potential in the greenhouse on chickpea and in combination with five Streptomyces sp. (strains CAI-24, CAI-121, CAI-127, KAI32, and KAI-90; demonstrated earlier as biocontrol potential against Fusarium wilt disease in chickpea), the traits, including nodule number and weight, shoot, and root weight, pod number and weight, seed number and weight, available phosphorus and % organic carbon were found significantly, enhanced over un-inoculated control. In the on-station and on-farm field conditions, IC-76 significantly enhanced nodule number and weight, shoot, and root weight, stover and grain yield and total dry matter. In the rhizosphere (0-15 cm soil), the bacterium also significantly enhanced the total nitrogen, available phosphorus and % organic carbon. The sequence of 16S rDNA gene of the IC76 was matched with Pseudomonas geniculata in BLAST analysis. This study demonstrates that IC-76 has the potential for PGP in chickpea. - Plant growth-promoting (PGP) microbes are soil bacteria that colonize rhizoplane and rhizosphere and enhance plant growth when inoculated artificially onto the soil or seeds. PGP bacteria can directly or indirectly affect plant growth through various mechanisms which includes fixation of atmospheric nitrogen (Soares et al. 2006), solubilization of minerals (Basak and Biswas 2009; Panhwar et al. 2012), synthesis of various enzymes and phyto-hormones (Patten and Glick 2002; Cheng et al. 2007), and inhibition of phytopathogens (Hao et al. 2011; Gopalakrishnan et al. 2011a, b, c). Different functional and taxonomic groups of microbes are reported to have PGP traits which includes free living bacteria, such as Bacillus, Pseudomonas, Erwinia, Caulobacter, Serratia, Arthrobacter, Micrococcus, Flavobacterium, Chromobacterium, Agrobacterium, Hyphomicrobium, and symbiotic N2 fixing bacteria, such as Rhizobium, Bradyrhizobium, Sinorhizobium, Azorhizobium, Mesorhizobium, and Allorhizobium (Vessey 2003). The use of PGP microbes has increased in many parts of the world due to their significant contribution in growth and yield which has been demonstrated in crops, such as tomato, wheat, rice, bean, and pea (Tokala et al. 2002; Nassar et al. 2003; ElTarabily 2008; Figueiredo et al. 2008; Sadeghi et al. 2012; Gopalakrishnan et al. 2012a, b, 2013a, b). In legumes, symbiotic bacteria including Rhizobium, Mesorhizobium, and Bradyrhizobium are reported to benefit plant growth and yield (Pandey and Maheshwari 2007; Joshi et al. 2008; Kumar et al. 2011). Besides, several non-symbiotic bacteria, including Pseudomonas, Bacillus, Klebsiella, Azotobacter, Azospirillum, and Azomonas were also reported to increase the plant growth by the same mechanisms followed by Rhizobium sp. (Glick 1995; Ahemad and Kibret 2014). Number of other bacteria such as Pantoeaagglomerans, Klebsiellapneumoniae, Beijerinckia sp., and Azoarcus sp. were also reported to fix atmospheric nitrogen and promote plant growth (Riggs et al. 2001). Minorsky (2008) demonstrated vigorous colonization of a PGP strain Pseudomonas fluorescens B 16 in the roots of tomato resulting in higher yield. In chickpea, fluorescent pseudomonads were reported to promote plant growth, nodulation, and nitrogen fixation (Parmer and Dadarwal 1999). Though a number of literatures are available for PGP of various functional groups of bacteria, the demonstration of PGP bacteria under on-station and on-farm field conditions are scarce. Therefore, the present investigation was aimed to characterize and evaluate a root nodule bacterium isolated from chickpea nodule for its ability to promote plant growth in chickpea under greenhouse, on-station and on-farm field conditions. Materials and methods A bacterium designated as IC-76, acquired from microbial gene bank at ICRISAT, was used extensively in this study. IC-76 was originally isolated from the nodules of chickpea (Cicer arietinum L.) by ICRISAT from the alluvial soils of Haryana, India. The actinomycetes CAI-24 (Streptomyces tsusimaensis; NCBI Accession Number: JN400112), CAI121 (Streptomyces caviscabies; NCBI Accession Number: JN400113), CAI-127 (Streptomyces setonii; NCBI Accession Number: JN400114), KAI-32 (Streptomyces africanus; NCBI Ac (...truncated)