M.Sc.

At present, the available biofertilizers are bulky and have short shelf life due to contamination problem. Hence, a suitable formulation needs to be developed which is less bulky and has increased shelf life. Alginate is one of the most commonly used polymers for microbial encapsulation. It is commercially extracted from seaweeds like Macrocystis pyrifera, Ascophyllum nodosum, Laminaria etc. The present study was undertaken in the Department of Agricultural Microbiology, College of Horticulture, Vellanikkara to develop an alginate based formulation of nitrogen, phosphorus, and potash biofertilizers consortia and evaluate for growth enhancement using tomato as the test crop. Five isolates each of nitrogen fixers, phosphorus and potassium solubilizers from Wayanad district were obtained from the repository maintained in the Department of Agricultural Microbiology, COH, Vellanikkara. The bacterial isolates were screened for nitrogen fixation, phosphorus and potash solubilization along with indole acetic acid production. Amount of nitrogen fixed (22.63 mg of N g -1 sucrose utilized) and indole acetic acid production (6 μg ml-1) were highest for Microbacterium arborescence. Similarly, Burkholderia cepacia recorded the highest amount of phosphorus solubilization (64.83 μg ml-1) and indole acetic acid production (8.67 μg ml-1). Among the potassium solubilizers, Acinetobacter calcoaceticus solubilized the highest amount of potassium (41.63 μg ml-1) under in vitro conditions.
Microbacterium arborescence, Microbacterium testaceum and Nguyenibacter vanlangensis were selected as the three most promising nitrogen fixers. Similarly, the phosphorus solubilizers selected were Burkholderia cepacia, Bacillus subtilis (KASB5) and Bacillus subtilis (H4). The potassium solubilizers selected were Acinetobacter calcoaceticus, Burkholderia sp. and Brevibacterium sp. Compatibility studies were conducted among the selected bacterial isolates using cross streak method which showed no inhibition at the intersection of two bacterial isolates. The compatible isolate was further confirmed by dual culture method. The efficient isolates selected for consortia preparation were Microbacterium arborescence + Burkholderia cepacia + Acinetobacter calcoaceticus (N1P1K1), Microbacterium arborescence + Bacillus subtilis (KASB5) + Acinetobacter calcoaceticus (N2P2K2) and Microbacterium testaceum + Burkholderia cepacia + Burkholderia sp. (N3P3K3).
In order to prepare a sterile and uniform sized alginate beads, a protocol was standardized for temperature, time and concentration of sodium alginate solution with calcium chloride solution. The optimum concentration of sodium alginate solution and temperature required for alginate beads preparation was 3% and 95 oC for 15 minutes. The diameter of alginate beads ranged between 2 mm – 2.7 mm. The rate of release of nitrogen fixers from alginate based consortia-1 during the initial 24 hours was high (41.67 x 106 cfu -1 g of beads) which reached to a population of 21 x 106 cfu -1 g of beads at 90th day. Population of nitrogen fixers, phosphorus solubilizers and potassium solubilizers decreased towards the 90th day when compared with the initial count of bacteria released from the alginate beads.
A pot culture experiment using tomato as a test crop was conducted under sterile and unsterile potting mixture separately to evaluate Alginate based consortia (T1, T2 and T3), combination (T1 + T2 + T3), Talc based consortia (T5, T6 and T7) and POP (T8), Organic POP (T9) and Absolute control (T10). In sterile soil, the population of nitrogen fixers were higher for all the treatments receiving bacterial consortia. The population of P-solubilizers were higher in alginate based consortium-1 (13.0 x 106 cfu g-1) while the population of K-solubilizers were higher in treatments with combined application of alginate based consortia. Under unsterile soil, the population of nitrogen fixers were found to be higher in treatments with alginate and talc based consortia. The population of potassium solubilizers was higher in treatment with combined application of alginate based consortia. Treatments with alginate based consortium showed a higher population of phosphorus solubilizers compared with talc based consortia in unsterile soil. However, the population of N fixers, P and K solubilizers decreased with time in all treatments. Compared to initial soil status, application of alginate based bacterial consortium-1 resulted in a significant increase in available nutrient content among treatments receiving bacterial consortia in sterile soil conditions. Yield and yield attributes were higher in the alginate based bacterial consortia-1(897.0 g/plant) under sterile condition. However, yield was higher in treatment based on POP under unsterile soil conditions (845.0 g/plant). Among alginate based treatments, alginate based consortium-1 recorded a higher yield (707.33g/plant) under unsterile condition also. The present studies indicated that the alginate based consortium could be a potential microbial inoculant formulation which is less bulky, free from contamination, biodegradable and non-toxic. Encapsulation enables slow and controlled release of cells and thus, maintains a uniform bacterial population. However, further studies are required to study its shelf life, its performance under field condition before commercialization and develop a suitable protocol for large scale production.