Enhanced symbiotic performance and productivity of drought stressed common bean after inoculation with tolerant native rhizobia in extensive fields

This study isolated and examined the performance of four selected strains of Rhizobium as growth enhancer inoculants of common bean (Phaseolus vulgaris) in saline- and drought-stressed fields located to the east and west of the Egypt Nile delta. Indigenous bean rhizobia were tested for salt tolerance by culturing and for taxonomic status by DNA analysis. Their nodulation and N2-fixation abilities under drought stress and persistence in biofertilizer formulations were evaluated, followed by assessment of their agronomic performance with common bean in 16 salt-affected, drought-stressed fields in combination with different doses of N-fertilizer applications in 2007 and 2008. Population dynamics studies with one model strain indicated good persistence in biofertilizer preparation. Inoculation with a test strain increased plant weight in the greenhouse from 2.718 to 3.314 g and four strains increased seed yield in saline/drought-stressed fields by 2.848⿿3.218 t ha⿿1 during seasons 2007 and 2008, respectively. Inoculation also increased straw production, harvest indices and the agronomic fertilizer N-use efficiency. The corresponding mean seed yields in adjacent uninoculated farmers⿿ fields exposed to the same intensity of aridification were 2.425 and 2.230 t ha⿿1, respectively. The study shows that locally-selected strains of rhizobia can be formulated into biofertilizers that significantly enhances seed yield and the agronomic N-use efficiency while providing a nature-based alleviation of the abiotic water deficit stress of intense aridification in saline- and drought-stressed fields.