ABSTRACT
Plant growth promoting rhizobacteria (PGPR) are free-living soilbacteria that colonize seeds and roots, and provide some benefit tothe host plant. These bacteria are distinct from symbiotic bacteria such as Rhizobia, that form nitrogen-fixing nodules on host legumes and therein provide the reduced nitrogen necessary for their host plants to grow in nitrogen poor soils, and from biocontrol bacteria that benefit host plants indirectly by inhibiting phytopathogenic bacteria (discussed in Chapters 4 and 5 in Volume 1 of this series (Microbial Biotechnology in Horticulture). Under consideration here are the associative PGPR that benefit their host plant by producing compounds or enzymes that directly contribute to plant growth. PGPR strains that are known to enhance plant growth belong to a variety of genera; the most thoroughly studied are Pseudomonas, Enterobacter, Bacillus, Azospirillum, Burkholderia, and Kluyvera (Glick et al., 1999; Reed and Glick, 2004). Many of these are available as commercial formulations under such trade names such as Azo-Green and Foundation RGP (Azospirillum brasilense); Zea-Nit (Azospirillum brasilense and Azospirillum lipoferum); Subtilex, Kodiak, Epic, Companion, and Serenade (all Bacillus subtilis); Deny and Intercept (Burkholderia cepacia); and Conquer and Victus (Pseudomonas fluorescens) (Fravel, 2005). Most of
them are described as effective biopesticides to combat root and foliar pathogens; however, a few of them, such as those containing Azospirillum spp., are marketed as biofertilizers for accelerated seed germination and increased root biomass (e.g., https://www.encoretechllc.com).
