RESUMEN
The production of plant growth promotors [indole acetic acid, gibberellic acid and abscissic acid] by rhizobacteria and cyanobacteria has been taken as a main criterion in the selection of the microbial strains used in this study. A field experiment was conducted at Sahl El Hussinia Station, El Sharkia Governorate, during the winter season of 2008/2009 to investigate the effect of rhizobacteria and cyanobacteria either individually or in combination on growth, yield and yield quality of sugar beet under salinity stress. Soil biological activity in terms of dehydrogenase activity was significantly affected by the biological treatments. The dehydrogenase recorded its highest value when the combined inoculum of rhizobacteria and cyanobacteria was applied. Inoculation with rhizobacteria and/or cyanobacteria in saline soil alleviated the salinity effects on the sugar beet and enhanced photosynthesis [leaves chlorophyll content], proline and phenoic accumulation in roots, along with, increasing the concentrations of N, P and K and decreasing Na[+] concentrations in roots. This physiological positive response of the plant growth promoting rhizobacteria and/or cyanobacteria resulted in significant increases in sugar beet root yield and yield quality [TSS, sucrose and purity%]. Best results were obtained by the combined mixture of bacteria and cyanobacteria followed by the individual treatments of either. This investigation pointed out that plant growth promoting substances secreted by rhizobacteria [PGPR] and cyanobacteria could be used as a good tool to alleviate salinity stress and promote sugar beet productivity and yield quality as it provides an ceo-friendly biological approach under saline soil conditions