“…PGPR can be divided into two groups according to their relationship with the plants: symbiotic bacteria and free-living rhizobacteria (Khan, 2005). As reviewed by Compant et al (2005), Glick (1995Glick ( , 2001, Hall (2002), Hallman et al (1997), Lucy et al (2004), Sturz et al (2000), and Welbaum et al (2004), a lot of work have been done on the mechanisms and principles of the PGPR-plant relationship, which was accepted widely as rhizosphere effect. Generally, PGPR function in three different ways (Glick, 1995(Glick, , 2001): synthesizing particular compounds for the plants, facilitating the uptake of certain nutrients from the environment (Çakmakçi et al, 2006;Lucas García et al, 2004a,b;Siddiqui and Mahmood, 2001), and lessening or preventing the plants from diseases (Guo et al, 2004;Jetiyanon and Kloepper, 2002;Raj et al, 2003;Saravanakumar et al, in press).…”