Abstract
Fluorescent Pseudomonas, aerobic, Gram-negative bacteria possess many traits that make them well suited as biocontrol and growth promoting agents. Our study revealed that isolates vary in mechanisms involved in the antagonist interactions against pathogen and growth stimulatory effects on host plant. Most of the potential antagonistic fluorescent Pseudomonas identified were avid iron chelators (P233, P201, 176, P76 and, P76). Wide variation in ACCd enzyme production was observed. ACCd enzyme assay tested P141 > P247 > P126, as potential ACCd enzyme producer. Cynogenic fluorescent Pseudomonas isolates P76 and P124 exerted strong inhibitory against S. rolfsii. However, another cynogenic fluorescent Pseudomonas P179 had no influence against R solani and S. rolfsii which remains unexplained. Noticeable crop specific plant growth stimulation exerted by different fluorescent Pseudomonas was observed on wheat (P124), chickpea (P72), lathyrus (P85, P216), greengram (P11), blackgram (P99, P233); bottlegourd (P248, P167); rice (P176, P247).
Highlights
Aerobic gram negative Fluorescent Pseudomonas spp. have emerged as the largest and potentially most promising group of plant growth promoting rhizobacteria involved in the bio-control of plant diseases (Weller et al 2002; Fravel 2005)
Isolates were characterized on the basis of biochemical tests as per the procedures outlined in Bergey’s Manual of Systematic Bacteriology (Sneath 1986) and tests reported by (Blazevic et al 1973) that differentiate the fluorescent Pseudomonas into P. aeruginosa, P. putida and P. fluorescence (Table 1)
Twenty-four isolates of fluorescent Pseudomonas were screened by different siderophore assay
Summary
Aerobic gram negative Fluorescent Pseudomonas spp. have emerged as the largest and potentially most promising group of plant growth promoting rhizobacteria involved in the bio-control of plant diseases (Weller et al 2002; Fravel 2005). A large number of secondary metabolites, growth hormones, antibiotics and chelating compounds such as siderophores (Choudhary et al 2009; Beneduzi et al 2012) are known to be released by these fluorescent pseudomonads They maintain soil health by employing a wide variety of mechanisms including nitrogen fixation, enhanced solubilization of phosphate and phytohormone production (such as auxin and cytokinin). Pseudomonas spp. produce an arsenal of antimicrobials (including hydrogen cyanide, HCN), pyoluteorin, phenazines, pyrrolnitrin, siderophores, cyclic lipopeptides and 2,4-diacetylphloroglucinol (DAPG) (Thomashow and Weller 1991; Weller 2007). This is considered as an indirect strategy to promote plant growth as well as the ability to induce systemic resistance in plants (Santoyo et al 2012; Glick 2014). Applications of these associations were investigated in Wheat (Triticum aestivum), Chickpea (Cicer arientinum), Lathyrus (Lathyrus sativus), Greengram (Vigna radiata), Blackgram (Vigna mungo), 27 Page 2 of 11
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