Isolation, Selection and Identification of Nitrogen Fixation Rhizospheric and Endophytic Bacteria from Maize (Zea Mays L.) Grown on the Soil

Maize (Zea may L)is an important food crop in the world economy and Vietnam. Maize kernels are used as human food, animal feed and raw materials for industry. Maize needs to absorb a large amount of fertilizers to grow and develop [1]. However, chemical fertilizer applied to maize too much will cause environmental pollution, harmful effects on human and animal health. High chemical nitrogen fertilization increases investment costs, causes imbalances in natural ecosystems such assoil erosion, increases in nitrate concentrations in surface water, groundwater and discharges nitrous oxide during denitrification [2]. In today'sagricultural production, improving soil fertility, reducing the amount of chemical fertilizers, increasing biological fertilizers and including N-fixing bacteria are necessary to develop sustainable agriculture. Nitrogen-fixing bacteria convert the free nitrogen of the biosphere to NH by ATP energy and catalysis enzyme nitrogenase under 3 normal conditions [3]. Plants absorb nitrogen to synthesize protein for growth and development.

Most microorganisms present in the rhizosphere play important roles in the growth and in the ecological fitness of their plant host [4]. Many studies showed that biofertilizer containing nitrogen fixing bacteria promoted plant growth and high yield could be achieved [5]. Several Plant Growth Promoting Rhizobia (PGPR) were isolated from maize grown infield soils such as Azospirillum lipoferum, Bacillus polymixa, Pseudomonas putida [6], [7]. Inoculated maize with Azospirillum sp. could support growth parameters including plant height. Nitrogen fixing bacteria such as Pseudomonas, Klebsiella, Enterrobacter, could use as growth promoters of maize plants [8]. Bacterial strains isolated from soil samples and maize roots include dominant bacterial genera identified were Klebsiella and Burksholderia potential as plant growth-promoting on maize plants [9]. Only inoculation of Azotobacter was done just a few hours before seed sowing. It helps on growth and yield of maize increasing 15 to 35% grain yield over non-inoculated treatments [10]. The results showed that strain AChad the highest nitrogen and phosphatase activity and it helped increase plant biomass up to 39%. In Vietnam, the application of PGPR for maize grown in the field was limited [11]. Dong Thap is a province in the Mekong River Delta, within the limit of 10°07'-10°58' North latitude and 105°12'-105°56' East. The area has alluvial soil with a pH range of 5.76-7.02 and freshwater where crops grow well. This province has a large maize growing area of 4,800 hectares, identified as the second-largest maize area in the Mekong Delta. However, Farmers often provide maize with a big amount of chemical fertilizers (180 kg N+135 kg P2O5+90 kg K2O/1ha) to get high grain yield (6-8 tons/ha). The fields must be irrigated, sprayed with herbicides, pesticides and especially urea with high prices, so investment costs are high and incomes are low.

The application of native, adapted microorganisms might improve yields by direct plant growth promotion and increasing grain yield, decreasing cost in maize cultivation in order to enhance income for the farmers. The aims of this study were (i) isolation and characterization of rhizospheric and endophytic bacteria (ii) studying characteristic such as nitrogen fixation and IAA production, (iii) the genetic diversity of isolated strains from maize plant and soil was evaluated in order to identify an efficient growth promotion strains that can be also improve the growth of maize plant as biofertilizer.