Response of faba bean plant to inoculation with heavy metals tolerant rhizobium leguminosarum biovar viceae and/or phosphate-dissolving bacteria

ABSTRACT

Many isolates of R. Ieguminosarum biovar viceae [8 isolates] and phosphate-dissolving [6 isolates] bacteria were isolated from soils irrigated with polluted sewage water with high concentrations of heavy metals [El-Gabal El-Asfar and El-Hamoul regions] and others irrigated with clean water [El-Riad region]. These isolates were evaluated for their tolerance to high concentrations of mixed Pb, Cd and Ni. High tolerant bacterial isolates were selected for inoculation of faba bean plants under gradient concentrations of these heavy metals mixture, in the greenhouse. Rhizobia and phosphate-dissolving bacterial isolates varied in their ability to tolerate high concentrations of heavy metals in YMA medium. Isolates from highly polluted soils revealed higher tolerance to YMA medium heavy metals than those isolated from clean soils collected from El-Riad region. Sandy soil washed with 0.1 N HCl were enriched with different concentrations of heavy metals mixture, i.e. Pb, Cd and Ni and sowed with faba bean seeds. The seedlings were inoculated with the rhizobial isolates. The isolates of RH6 and RH8 showed the highest records of plant dry weight [g], number and dry weight of nodules/plant, and N%. Phosphate-dissolving isolates varied for their tolerance to heavy metal pollution in nutrient broth medium. The isolates of B4 and B6 were the most tolerant and gave highest alkaline phosphatase activity [15.15 and 13.45, mg/g/h]. Results indicated that combined inoculation with RH8+B6 increased faba bean yield components especially seeds over uninoculated N-fertilized control. N and P concentrations in seeds were, also, increased but, heavy metal concentrations decreased. Thus, inoculation of faba bean plants with heavy metal tolerant S. Ieguminosarum biovar viceae and phosphate-dissolving bacteria is recommended to apply in heavy metals polluted soils