Biological control of soil-borne pathogens comprises the decrease of inoculum or of the disease producing activity of a pathogen through one or more mechanisms. Interest in biological control of soil-borne plant pathogens has increased considerably in the last few decades, because it may provide control of diseases that cannot or only partly be managed by other control strategies. Recent advances in microbial and molecular techniques have significantly contributed to new insights in underlying mechanisms by which introduced bacteria function. Colonization of plant roots is an essential step for both soil-borne pathogenic and beneficial rhizobacteria. Colonization patterns showed that rhizobacteria act as biocontrol agents or as growth-promoting bacteria form microcolonies or biofilms at preferred sites of root exudation. Such microcolonies are sites for bacteria to communicate with each other (quorum sensing) and to act in a coordinated manner. Elicitation of induced systemic resistance (ISR) by plant-associated bacteria was initially demonstrated using Pseudomonas spp. and other Gram-negative bacteria. Several strains of the species Bacillus amyloliquefaciens, B. subtilis, B. pasteurii, B. cereus, B. pumilus, B. mycoides, and B. sphaericus elicit significant reductions in the incidence or severity of various diseases on a diversity of hosts. Elicitation of ISR by these strains has been demonstrated in greenhouse or field trials on tomato, bell pepper, muskmelon, watermelon, sugar beet, tobacco, Arabidopsis sp., cucumber, loblolly pine, and two tropical crops (long cayenne pepper and green kuang futsoi). Protection resulting from ISR elicited by Bacillus spp. has been reported against leaf-spotting fungal and bacterial pathogens, systemic viruses, a crown-rotting fungal pathogen, root-knot nematodes, and a stem-blight fungal pathogen as well as damping-off, blue mold, and late blight diseases. This progress will lead to a more efficient use of these strains which is worthwhile approach to explore in context of biocontrol strategies.

Plants possess a range of active defense appa-

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Maize seeds were bacterized with siderophore-producing pseudomonads with the goal to develop a system suitable for better iron uptake under iron-stressed conditions. Siderophore production was compared in fluorescent Pseudomonas spp. GRP3A, PRS9 and P. chlororaphis ATCC 9446 in standard succinate (SSM) and citrate (SCM) media. Succinate was better suited for siderophore production, however, deferration of media resulted in increased siderophore production in all the strains. Maximum siderophore level (216.23 microg/ml) was observed in strain PRS9 in deferrated SSM after 72 h of incubation. Strains GRP3A and PRS9 were used for plant growth promotion experiments. Strains GRP3A and PRS9 were also antagonistic against the phytopathogens, Colletotrichum dematium, Rhizoctonia solani and Sclerotium rolfsii. Bacterization of maize seeds with strains GRP3A and PRS9 showed significant increase in germination percentage and plant growth. Maximum shoot and root length and dry weight were observed with 10 microM Fe3+ along with bacterial inoculants suggesting application of siderophore producing plant growth promoting rhizobacterial strains in crop productivity in calcareous soil system.