Survival of bradyrhizobium japonicum as affected by soil texture and sodium chloride concentration

ABSTRACT

Survival of three Bradyrhizobium japonicum strains [110, 118 and 209] in different soil types [clay, sand, calcareous, saline and alkaline] was investigated in laboratory experiment. Rhizobial numbers were increased with time reaching the maxima between the 5th and the 15th day of incubation at 30C then decreased in rates varied according to soil type and strain involved. Supplementation of soil with yeast mannitol broth stimulated the bacterial growth in all soils except in saline soil where counts were increased up to 4000 times of that recorded in soils received sterile tap water. In alkaline soil, B. japonicum strains could not grow when introduced into soil in low densities and were progressively decreased with time when inoculated in soil in higher densities. The multiplication of all tested strains was stimulated when sodium chloride was added to yeast mannitol broth medium in the level of 100 meq 1-1. Increasing the salt concentration seriously repressed the bacterial survival and no growth was observed in the presence of 1000 meq NaCl 1-1 in most cases