A comparison study between the isolated indigenous bacteria and chemical Zn fertilizer (ZnSO 4 .7H 2 O) was conducted to evaluate their potential to augment Zn nutrition of Zn responsive (NDR 359) and Zn non responsive (PD 16) varieties of rice under the green house. Three bacterial strains namely; BC, AX and AB isolated from a Zn-deficient rice-wheat field belonging to the genera Burkholderia and Acinetobacter were investigated for the growth promotion and Zn uptake in rice plants. The plant growth promotory properties such as Zn solubilization and IAA production of the isolates was checked in a previous study. These three isolates when used individually or in combination were found effective in significantly increasing the mean dry matter yield/pot (12.9%), productive tillers/plant (15.1%), number of panicles/plant (13.3%), number of grains/panicle (12.8%), grain yield (17.0%) and straw yield (12.4%) over the control and Zn fertilizer treatment, respectively. Bacterial inoculations also significantly enhanced the total Zn uptake/pot (52.5%) as well as grain methionine concentration (38.8%). Effect of bacterial treatments on the bioavailability of Zn was assessed by estimating the levels of phytic acid in grains. A reduction of nearly 38.4% in phytate: Zn ratio in grains was observed under bacterial inoculations.
Low Zn in staple food grains like rice is closely related to large scale Zn malnutrition in many countries of the World. Zinc biofortification of rice grains by some cost effective agronomic method is important for low income farmers. To explore the possibility of enhancing the bioavailability of Zn in rice grains besides higher yields of two cultivars, the combinations of varying Zn fertilizer doses with or without inoculation of rhizobacteria consortium under split plot design set up were evaluated in two years field trials. Microbial inoculation + 5 kg Zn ha-1 to I year rice crop resulted in the highest number of effective tillers, grain yields, Zn concentration and uptake in grains and straw and total Zn uptake in both years. Grain yield of rice during two years increased by 19.7-27.9 and 17.1-20.4 percent over control under treatments receiving microbial inoculation + 5 kg Zn ha-1 to I year rice and 5 kg Zn ha-1 alone to I year rice crop, respectively. The highest concentration of Zn (10.9-19.1 mg kg-1) and the lowest concentration of phytic acid (18.5-25.3 g kg-1) in dehulled rice grains were recorded with soil application of 5 kg Zn ha-1; however, the values were at par with those observed under microbial inoculation + 5 kg Zn ha-1 (12.0-17.0 mg Zn kg-1 and 19.2-26.9 g phytic acid kg-1). The percent utilization of soil applied Zn increased with microbial inoculation in both the years and it was relatively higher in NDR 359 as compared to PD 16.
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