INDUCING PLANT RESISTANCE AGAINST SALINITY USING SOME RHIZOBACTERIA

Activity of 1-aminocyclopropane-1-carboxylate (ACC)-deaminase of rhizobacteria isolated from salt-stressed rhizospheres were screened based on their utilization of ACC as sole nitrogen source. Twenty percentage of the isolates achieved remarkable differences in the activities of ACC-deaminase ranged from 180 to 1398 nm α-ketobutyrate mg^-1 h^-1. Phylogenetic analysis of 16S rRNA sequence of two strains with the highest level of ACC-deaminase activity revealed the first isolate was identified as Alcaligenes faecalis subsp. parafaecalis strain G and the second as Alcaligenes faecalis strain NBRC 13111. The influence of ACC-deaminase rhizobacteria on the ACC-induced classical triple response in etiolated wheat seedlings were studied. Results revealed that exogenous application of 3 mmol L^-1 ACC creating classical triple response in seedlings under salt stress (10% NaCl). Inoculation with two ACC-deaminase rhizobacteria decreased the ACC-imposed classical triple response in etiolated seedlings, as significant increases in seedling length,  root elongation and reduction in stem diameter over uninoculated ACC-stressed control were recorded. Studying the effect of salinity ranged from 0 to 10% NaCl on the growth and ACC-deaminase activitiy of the two bacterial strains revealed that gradual reduction in both growth and enzyme activity were demonstrated with increasing salinity. Both strains could tolerate the salinity up to 7% NaCl, A. faecalis strain G showed the highest ACC-deaminase activity at 1% concentration of NaCl, while A. faecalis strain NBRC recorded the highest enzyme activity at 3% NaCl.
                       Two field experiments were conducted during 2014/15 and 2015/20116 at Ras Sudr Experimental Station to evaluate the effect of ACC-deaminase bacteria on the growth and productivity of wheat under salt stress condition. For all yield traits and chemical constituents of wheat grains, significant increase were recorded under ACC-deaminase bacterial inoculation comparing to control in both seasons of planting. The highest increase in the total microbial counts, CO₂ evolution and dehydrogenase activity of the rhizosphere regions were indicated in plants inoculated with bacterial strains regardless the type of bacteria used. The results indicated that inoculation with ACC-deaminase rhizobacteria can serve as promising economical alternative alleviated plant stress caused by salinity.