Plant probiotics in phosphorus nutrition in crops, with special reference to rice

Abstract

Low level of soluble soil phosphorus (P) is a serious constraint in crop production in tropical and subtropical soils. Many plant-associated bacteria or plant probiotics can solubilize P from either organic- or inorganic-bound phosphates thereby facilitating plant growth. Understanding the bacterial contribution to plant P nutrition and opportunities for manipulating specific bacterial strain to enhance P availability in soil has, therefore, been of considerable interest over many decades. This interest is accentuated by rising costs of P fertilizer and because of low efficiency of P use by plants from soil and fertilizer sources. Bacteria from diverse taxonomic genera such as Pseudomonas, Bacillus, Klebsiella, Streptomyces, Burkholderia, Pantoea, Enterobacter, etc., can solubilize soil insoluble P and increase growth and yield of crops. The widely recognized mechanisms of phosphate solubilization mediated by these plant-associated bacteria are production of organic acids (such as gluconic, citric, and oxalic) and/or secretion of hydrolytic enzymes (such as phytases, phosphatase, etc.). Despite their potential as low-input practical agents for plant P nutrition, application of phosphate solubilizing bacteria (PSB) has been hampered by their inconsistent performance in the field. Hence, the full potentials of PSB have not yet been achieved for P nutrition in major crop production. Therefore, better understanding on how they interact with roots and other organisms in the rhizosphere is needed. This chapter reviews advances on PSB research and their potential for phosphorus nutrition in crop plants, with special reference to rice. Mode of action of phosphate solubilization by bacteria and their uses as biofertilizer for eco-friendly low-input sustainable crop production are also discussed.