Rice blast caused by Magnaporthe or

Rice blast caused by Magnaporthe oryzae B.Couch [Pyricularia grisea (Cooke) Sacc.] is the most destructive rice disease worldwide causing grain yield losses of staggering dimension. Yield losses up to 100% have been recorded in a recent outbreak of blast in Brazil, in a newly released upland rice cultivar Colosso (Prabhu et al.,2009).
In an ecologically sustainable agriculture, blast disease control requires integrated management of genetic resistance, cultural practices and chemical control.
The durability of genetic resistance in improved rice cultivars is limited due to high variability of the pathogen (Ou, 1980).
Consequently the application of fungicides has been intensive in Brazil for reducing yield losses. The use of resistance inducers, biotic as well as abiotic, are currently being
explored under commercial scale as major strategies for increasing the durability of disease resistance and reducing toxic residues resulting from indiscriminate use of chemicals.
Rhizobacteria are known to suppress plant diseases caused by fungal pathogens and to promote plant growth.
The application of rhizobacteria in crop soils has direct and indirect benefits to agricultural production and permit judicious use of agricultural inputs (Lavie and Stotzky, 1986).
In addition to improving plant growth, rhizobacteria are directly involved in synthesis of phytohormones, solubilization of minerals such as phosphorus and production of siderophores and iron chelates (Glick et al., 1995;Bowen and Rovira, 1999).
Besides mineralization, the rhizobacteria may control plant pathogens and harmful microorganisms through the production of antibiotics and degradation of cell wall by different
enzymes (Antoun and Kloepper, 2001).
The reduction of disease severity in plants by plant growth promoting rhizobacteria (PGPR) may occur by different mechanisms of suppression, such as competition for nutrients, antibiosis
through antimicrobial metabolite production (Ramamoorthy et al., 2001) and inducted systemic resistance (ISR) (Van Loon and Pieterse, 2006; Van Loon, 2007). The systemic resistance induction process increases enzymatic activity of peroxidase (PO) and phenol oxidase (PPO) which are responsible for catalyzing lignin formation, and phenyl ammonia lyase (PAL) which is involved in the biosynthesis of phytoalexins and phenols. ISR induction also increases liposaccharides, a constituent of cell wall membranes (LPS) (Radjacommare et al., 2004). The pathogenesis-related proteins (PRPs) b-1,3-glucanase and chitinase, enzymes that
belong to PR-2 and PR-3 families, respectively (Van Loon and Pieterse, 2006) have been related more often to SAR and sometimes to ISR. All these enzymes have been shown to be involved
in plant defense against pathogens in several pathosystems (Kini et al., 2000).
The benefits of rhizobacterial associations have been observed in various plant species such as chickpeas, eggplant (Kumar,1998), beets (Thrane et al., 2000), radish (Leeman et al., 1995), sorghum (Chiarini et al., 1998), tomato (Hoffmann-Hergarten et al.,
1998), ornamentals (Yuen and Schroth, 1986) and cereals (Biswas et al., 2000). The use of PGPR to control rice blast disease has been observed by several other authors, however, these studies were performed with isolates from rice grown under irrigated conditions (Krishnamurthy and Gnanamanickam, 1998; Radjacommare et al.,2004).
Lucas et al. (2009) studied the use of two strains of PGPR in the integrated management of rice blast in southern Spain and observed that there is a direct relationship between inoculation
of seed with rhizobacteria and disease control, grain yield improvement and head yield.
There is no information on the effect of PGPR in stimulating plant growth and disease suppression in aerobic rice. In the present study, attempts were made to select rhizobacteria associated with upland rice roots which are capable of promoting growth stimulation
as well as rice leaf blast disease suppression.