Useful Carriers for Cyanobacteria: Their Response to Cyanobacterial Growth, Acetylene-Reductase Activity, Cyanobacterial Grazers and Paddy Yield in Calcareous Soil |
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Authors: | M N Jha A N Prasad |
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Institution: | (1) Department of Microbiology, Faculty of Basic Sciences & Humanities, Rajendra Agricultural University, 848125 Pusa, Samastipur, Bihar, India |
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Abstract: | Summary Snails and nematodes, the potential cyanobacterial grazers, differ in their choice for cyanobacterial diet. Snails prefer
non-mucilaginous forms while nematodes prefer mucilaginous forms. Such differences in feeding choice between the cyanobacteria
suggests that it may not be possible to select strains of diazotrophic cyanobacteria that are resistant to all grazers. The
potential consumption of cyanobacteria at an average field density of 20,000 snails ha−1 was estimated to be about 50 kg (fresh weight) ha−1 day−1. Dorylamus sp. was most dominant nematode associated with cyanobacterial consumption. Phytoextracts of neem (Azadirachta indica), bel (Aegle marmelos) and tobacco (Nicotiana tabacum) were effective in controlling these cyanobacterial grazers. The minimum concentration of neem, bel and tobacco phytoextract
in water for 100 % mortality of snails were 0.1, 2.0 and 0.05%, respectively. However, trepellent level was only 0.01% for
neem and tobacco phytoextract. Complete mortality of nematode (Dorylamus spp.) required a higher concentration level (2%) even in the most effective tobacco phytoextract. Lower levels of phytoextract
(0.1%) were found to stimulate growth and nitrogen fixation of cyanobacteria. Application of these plant biomasses resulted
in significant increase in cyanobacterial acetylene-reducing activity (ARA) and rice yield and a significant decrease in snail
and nematode population. Augmentation of cyanobacterial acetylene-reducing activity was two to three times higher in comparison
to the control in both the years of experimentation. Rice yield also increased between 3.8 and 58.5% over the control, depending
on the quantity and nature of plant biomass. Tobacco waste was significantly superior in comparison to neem and bel biomass
as carrier of cyanobacterial culture. |
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Keywords: | Acetylene-reductase activity cyanobacteria growth nematode snail |
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