Novel Phl-producing genotypes of finger millet rhizosphere associated pseudomonads and assessment of their functional and genetic diversity

Abstract

Genetic diversity of phlD gene, an essential gene in the biosynthesis of 2,4-diacetylphloroglucinol, was studied by restriction fragment length polymorphism (RFLP) in 20 Phl-producing pseudomonads isolated from finger millet rhizosphere. RFLP analysis of phlD gene displayed three patterns with HaeIII and TaqI enzymes. phlD gene sequence closely correlated with RFLP results and revealed the existence of three new genotypes G, H and I. Further, the phylogenetic and concatenated sequence analysis of the 16S rRNA, rpoB, gyrB, rpoD genes supported the hypothesis that these genotypes G, H and I were different from reported genotypes A-F. In all phylogenetic studies, the genotype G formed a distant clade from the groups of Pseudomonas putida and P. aeruginosa (sensu strictu), but the groups H and I were closely related to P. aeruginosa/P. stutzeri group. The Phl-producing pseudomonads exhibited antagonistic activity against Pyricularia grisea (TN508), Gaeumannomyces graminis (DSM1463), Fusarium oxysporum (DSM62297), Xanthomonas campestris (DSM3586) and Erwinia persicina (HMGU155). In addition, these strains exhibited various plant growth-promoting traits. In conclusion, this study displays the existence of novel Phl-producing pseudomonads genotypes G, H and I from finger millet rhizosphere, which formed taxonomically outward phylogenetic lineage from the groups of P. putida and P. aeruginosa (sensu strictu).

Potential of Finger Millet Indigenous Rhizobacterium Pseudomonas sp. MSSRFD41 in Blast Disease Management—Growth Promotion and Compatibility With the Resident Rhizomicrobiome

“…Strain MSSRFD41 significantly suppressed mycelial growth of P. grisea in dual plate culture assays, consistent with antifungal action through the production of secondary metabolites, antibiotics, volatiles and hydrolytic enzymes (Sekar and Prabavathy, 2014 ). Pseudomonads are known to produce a wide range of metabolites including antibiotics (2,4-DAPG, HCN, PLT, and PCA) and enzymes that exhibit antagonistic activity against phytopathogens (Jegan, 2015 ; Müller et al, 2016 ; Vacheron et al, 2017 ; Yan et al, 2017 ).…”

“…Pseudomonas sp. MSSRFD41 was isolated from the rhizosphere of finger millet cultivated in the Dharmapuri district of Tamil Nadu, India (Sekar and Prabavathy, 2014 ). The active culture was maintained in King's B agar (KBA) medium (King et al, 1954 ) at 28°C and stored at −80°C in phosphate-buffered 20% (v/v) glycerol.…”

“…The unweighted pair group with mathematical average (UPGMA) algorithm was performed for cluster analysis with similarity matrices for generation of a dendrogram. Rhizobacterial isolates showed similar fingerprinting pattern to reference DNA were identified using 16S rRNA sequencing as described by Sekar and Prabavathy ( 2014 ).…”

“…Among the plant-associated microbes, pseudomonads are dominant bacteria known to protect plants against several phytopathogens (Radjacommare et al, 2005 ; Waghunde et al, 2013 ; Yin et al, 2013 ; Sekar and Prabavathy, 2014 ; Wang et al, 2015 ), and to promote plant growth under several abiotic stress conditions (Wang et al, 2015 ; Jegan et al, 2016 ). The biocontrol ability of pseudomonads is directly correlated with production of various antibiotics such as 2,4-diacetylphloroglucinol (2,4-DAPG), phenazines, pyrrolnitrin (PRN), pyoluteorin (PLT), hydrogen cyanide (HCN), and lytic enzymes (Radjacommare et al, 2005 ; Sekar and Prabavathy, 2014 ; Wang et al, 2015 ; Ganga et al, 2016 ). Among these, 2,4-diacetylphloroglucinol (DAPG) exhibits a broad range of antagonistic activity against phytopathogens, and can induce host plant systemic resistance (Weller et al, 2012 ; Jegan et al, 2016 ; Viswanath et al, 2016 ; Yan et al, 2017 ).…”

“…Pseudomonas sp. MSSRFD41, isolated from the rhizosphere of finger millet in India, is a novel 2,4-DAPG-producing strain with potential biocontrol and plant growth promoting traits (Sekar and Prabavathy, 2014 ). The present investigation aims (i) to assess the potential traits of MSSRFD41 involved in the inhibition of P. grisea, in vitro ; (ii) to determine the survival of MSSRFD41 in the rhizosphere and its impact on the rhizosphere microbial community; and (iii) to determine the efficacy of MSSRFD41 in blast disease control and growth promotion in finger millet under field conditions.…”