Department of Plant-Microbe Interactions, National Botanical Research Institute, Lucknow - 226 001, India

Background and objectives
256 bacterial strains representing different morphological types were screened for their biocontrol activities [1] under in vitro conditions. Pseudomonas spp. NBRI 19926 was selected for further studies because of its unique ability to inhibit the three fungi Fusarium oxysporum f.sp. ciceri, Rhizoctonia bataticola and Pythium spp. Since Fusarium causes extensive losses in crop production, further field-level evaluation of the microbial strain was conducted in a field which has 5 decades' history of Fusarium infection at Chandra Shekhar Azad University of Agriculture and Technology, Kanpur, UP, India.

Materials and methods
Pseudomonas NBRI-strain number 19926 was mass cultured in nutrient broth and centrifuged. The active bacterial cells were suspended in ordinary water for inoculum. Chickpea, Cicer arietinum, var. Radhey, a susceptible cultivar, was sown in October. Inoculations were done with the inoculum prepared as above. Regular tracking of the bacteria was done at monthly intervals. The control rows were sown without inoculum. The regular observations were conducted for the incidence of the disease and other growth parameters. Fusarium population was also estimated at the 3 month stage of the plant when disease onset was observed. A pot experiment was also conducted for the mechanism of biocontrol. The seeds were sown in soil prepared with fungus followed by bacterial inoculations.

Results and conslusions
The biocontrol experiments conducted at field are mean of four independent sets and five observations. The disease in inoculated rows was 15.3% whereas in control rows it was 22% indicating a control of 30-45% in treated rows. There was an increase in dry weight of root system and shoot system, respectively, of 24.16 and 46.20%. The number of pods per plant was significantly higher in inoculated plants, however the dry weight of 100 mature seeds was, respectively, 18.68 g treated and 18.10 g control. The increase in height as well as dry weight of the whole plant was recorded. Scanning electron microscopy done on the pot experiment with fungal and bacterial inoculation revealed the colonization of fungal mycelium leading to lysis of the fungus.

In summary, the Pseudomonas spp. isolate is a potential growth promoter leading to an increase in yield. The inoculum significantly keeps the disease under check, and the method is both economical and environmentally friendly.

1. Shekhar Nautiyal C, 1997. FEMS Microbiology Ecology 23, 145-155.