Screening Of Plant Growth-Promoting Bacteria And Their Regulation On Maize Salt Tolerance

Maize(Zea mays L.)is an important food crop,feed crop,cash crop and industrial raw material crop in the world.In recent decades,the consumption of maize increased gradually due to the growing population and the development of the livestock industry.As a main cereal crop,maize is grown in most provinces in China.Soil salinity is one of the major stresses to maize that causes inhibitory effects on maize growth and decreases in its yields and qualities.Therefore,it is urgent to alleviate NaCl stress of maize to improve corn kernel yields and qualities.In the present study,numerous plant growth-promoting bacteria(PGPB)were separated from plants(grown in saline areas)and their rhizospheric soils.The alleviation of PGPB on NaCl toxicity to maize seedlings also been tested under hydroponic and soil condition.The results provide the evidence and method to improve salt tolerance and biomass of maize by PGPB under saline condition.The main results of this study are as follows:1.More than 300 strains have been isolated from different plant species and their rhizospheric soils.There are 223,40 and 17 strains that can grow on LB solid medium containing 5%,10%and 15%NaCl,respectively.A total of 13 strains were selected from 40 strains which are tolerant to 10%NaCl according to their IAA secretion,nitrogen fixation,phosphorus dissolution,iron-producing carrier and ACC deaminase abilities.Under hydroponic condition,two strains(Hm18 and Pt07)were testified to improve the growth of maize seedlings significantly under NaCl stress.Based on the results of 16S rDNA sequence,physiological and biochemical identification analysis,Hm18 was identified as Bacillus altitudinis sp.and Pt07 was Pantoea sp.2.Hm18 and Pt07 effectively alleviate NaCl stress and promote the growth of maize seedlings under hydroponic condition.The increase in the elongation and biomass of the shoots and roots of maize,the chlorophyll contents,root vitalities and soluble protein contents were observed compared to the treatments without PGPB.Under NaCl stress,the chlorophyll,soluble protein contents,and root vitalities of maize seedlings increased by about 30%,20%-30%,and 15%-30%,respectively,and malondialdehyde contents and relative conductivities of leaves decreased by 7%-20%in the presence of PGPB.Hm18 and Pt07 reduced Na+ concentrations in shoots and roots of maize by 20%-40%,and increased K+concentrations by 5%-20%,improved K+/Na+ ratio and salt tolerant abilities of maize seedlings.3.Hm18 and Pt07 effectively alleviated NaCl stress,incease the enlongation and biomass of maize seedlings under soil culture.Under NaCl stress,inoculation with Hm 18 and Pt07 resulted in the increase of the soluble protein contents by 31.73%-39.12%,and the decrease of the malondialdehyde contents and relative conductivities of the leaves by 10%30%.The PGPBs significantly decrease in Na+ concentrations,while increase in K+,Ca2+concentrations and K+/Na+ratios of maize shoots and roots.The results indicatedthat Hm18 and Pt07 improved the salt tolerance of maize by promoting the absorption of K+ and Ca2+,and reducing Na+ concentrations.Two PGPBs selected from roots of plants grown in saline soil enhanced the growth of maize seedling,and improved the salt tolerance of maize.The results of the present study provides a practical basis for maize planting in saline soil.