Plant Growth Promoting Rhizobacteria -A Promising Tool for Eco-friendly Agriculture

摘要

Worldwide agricultural practice is moving to a more sustainable and environmental friendly approach due to increasing demand of safe food and awareness of the environmental and human health damage induced by overuse of pesticides and fertilizers (Aviset al, 2008). In this context, soil microorganisms with beneficial activity on plant growth and health represent an attractive alternative to conventional agricultural. In recent years, several microbial inoculants have been formulated, produced, marketed, and applied successfully by an increasing number of growers (Reed and Glick 2004). Although all parts of the plant are colonized by microorganisms, the rhizosphere represents the main source of bacteria with plant-beneficial activities. These bacteria are generally defined as plant growth promoting rhizobacteria (PGPR) (Bashan and Holguin, 1998). Plant growth promoting rhizobacteria (PGPR) influence plant health and productivity by two prime mechanisms-1) Direct mechanism viz. increased nutrient availability and phytohormone production 2) Indirect mechanism involving control of phytopathogens. Research on PGPR has been increasing at an ever increasing rate since the term was first used by Kloepper and coworkers in the late 1970s (Kloepper and Schroth, 1978). TodayPGPR are commonly used in developing countries, and inoculants are used on millions of hectares of land (Zehnder et al., 2001). Nevertheless, implementation of this biotechnology has been hindered by the lack of consistency and variation in responses that are obtained in field trials from site to site, year to year, or for different crops (Lambert and Joos, 1989). PGPR have been subjected to numerous investigations focused on biotechnological applications in agriculture, horticulture, forestry and environmental protection (Zahir et al, 2004). PGPR strains are broadly distributed among many taxa including Actinobacteria, Bacteroidetes, Cyanobacteria, Firmicutes and Proteobacteria (Tilak et al., 2005).