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The study entitled “Development of inoculant cultures of nitrogen fixing
cyanobacteria from wetland ecosystem of Vellayani” was conducted during the year
2019-2021 in the Department of Agricultural Microbiology, College of Agriculture,
Vellayani, Thiruvananthapuram with the objective to isolate and characterize
cyanobacterial strains with efficient nitrogen fixing capacity from wetland ecosystem
of Vellayani and assess the plant growth promotion and biocontrol activity through in
vitro screening process.
Ten nitrogen fixing cyanobacteria were isolated from wetland ecosystem of
Vellayani region and they were designated as VLY 1 - VLY 10. Tentative taxonomic
identification of the isolates were done based on their morphological and biochemical
characters. The isolates were tested for their pigment concentration like chlorophyll a,
phycobiliproteins, carotenoids. The chlorophyll a concentration varied from 0.688 mg
mL-1 to 5.372 mg mL-1. The phycocyanin, allophycocyanin and phycoerythrin
concentrations ranged between 0.016 mg mL-1 to 0.036 mg mL-1,0.015 mg mL-1 to
0.037 mg mL-1 and 0.005 mg mL-1 to 0.017 mg mL-1 respectively. Maximum
chlorophyll a and phycobiliproteins was recorded in Aphanocapsa sp.VLY 2.
Carotenoid concentration ranged between 0.001 μg mL-1 to 0.006 μg mL-1 and the
maximum was reported in Calothrixsp.VLY 10. The concentration of total proteins
ranged between 102.57 μg mL-1 to 236.32 μg mL-1 and the maximum was reported in
Oscillatoriasp.VLY 5. Antibiotic sensitivity profiling of the isolates was done against
streptomycin (25 μg), tetracycline (10 μg), nalidixic acid (30 μg), penicillin (10 μg),
erythromycin (15 μg), rifampicin (5 μg) and chloramphenicol (30 μg). The isolates
like Aphanothecasp.VLY 1, Oscillatoriasp.VLY 5, Lyngbyasp.VLY 7,
Chrococcussp.VLY 9 showed sensitivity against rifampicin with a sensitivity zone of
14mm, 10mm, 9mm, 11mm respectively. The isolate Aphanothecasp.VLY 1 showed
sensitivity against streptomycin and tetracycline with a zone of 12mm and 8mm
respectively. Oscillatoriasp.VLY 5 was sensitive against tetracycline with a zone of
13mm.
The cyanobacterial isolates were tested for their plant growth promotion activity
studies. Extracellular ammonia production ranged between 111.74 μmol mL-1 to 171
μmol mL-1 and maximum was reported by Chrococcussp.VLY 6. Nitrogen content of
the isolates ranged between 0.200 mg mL-1to 0.280 mg mL-1 and the isolate
Oscillatoriasp.VLY 5 reported the maximum nitrogen content. The Indole Acetic
Acid production ranged between 1.47 μg mL-1 to 7.10 μg mL-1. Maximum IAA
production was recorded in Chrococcussp.VLY 6. The antagonistic activity of the
isolates against plant pathogenic bacteria (Xanthomonas oryzae) and fungi (Pythium
ultimum, Phytophthora capsici, Fusarium oxysporumf.sp. solani, Rhizoctonia solani)
was investigated using disc diffusion method. The isolate Aphanothecasp.VLY 1 and
Microcystissp.VLY 3 showed antagonistic activity against Xanthomonas oryzaewith
an inhibition zone of 7.12 mm amd 8.20 mm respectively. The cyanobacterial isolates
were screened based on weighted average ranking and Chrococcussp.VLY 6 was
selected and evaluated for growth promotion under in vitro condition in rice. The rice
seeds were subjected to thirteen treatments such as T1 – 10 mL sterile distilled water,
T2 – 10 mL sterile BG-11 medium(without tryptophan). T3 – 10 mL sterile BG-11
medium amended with 5 mg mL-1 tryptophan, T4 to T8– 10mL sterile distilled water
mixed with 20 μL, 40 μL, 60 μL, 80 μL, 100 μL of cyanobacterial extract (culture
medium amended without tryptophan), T9 to T13 – 10 mL sterile distilled water mixed
with 20 μL, 40 μL, 60 μL, 80 μL, 100 μL of cyanobacterial extract (culture medium
amended with 5 mg mL-1 tryptophan). Maximum germination percentage was
observed in seeds treated with 10 mL sterile distilled water and 40 µL cyanobacterial
culture in BG 11 amended with 5mgmL-1of tryptophan.Also this treatment recorded
the maximum shoot length (6.83 cm), root length (12.23 cm), shoot dry weight (4.62
mg), root dry weight (2.91 mg), seedling vigour index (1781) and shoot root ratio
(2.7).
Based on the results of present study, Oscillatoriasp.VLY 5 and
Chrococcussp.VLY 6 are the superior isolates for plant growth promotion. Also,
Microcystissp.VLY 3 is the best among the isolates which showed antibacterial
activity.