Symbiotic efficiency, biosorption and the growth of rhizobia on Horse gram plants under aluminium stress

The aim of the present study was to evaluate the tolerance potential of Horse gram rhizobia to aluminium (Al) toxicity, the enhancement in pod formation, symbiotic efficiency and biosorption potential in the rhizobia inoculated Horse gram (Macrotyloma uniflorum (Lam.) Verdc.) plants. Initially, 32 isolates of Horse gram rhizobia were screened for their tolerance of Al in growth media. Among the 32 strains, HGR 4, 6, 13 and 25 that were more tolerant were inoculated individually to Horse gram plants and the plants were then screened for the ability of pod formation, symbiotic efficiency and biosorption potential. Among them, maximum pod formation was observed in Horse gram upon inoculation with HGR-6 and grown at 400 µg g-1 of Al. Maximum nodulation was observed in Horse gram upon inoculation with HGR-6 and HGR-13 grown at 200 µg g-1 Al. Leghaemoglobin content was maximumon inoculation with HGR-13 at 400 µg g-1 of Al. The strain HGR-13 has shown biosorption potential in soil and as well as in root nodules even at 300 µg g-1 of Al though it was maximum at 100 µg g-1. This study demonstrated that the Horse gram plantsinoculated with Rhizobium strains HGR - 4, 6, 13 and 25, besides having nitrogen fixing ability also have the ability to grow in Al contaminated soils. Hence, Horse gram plants associated with these strains of rhizobia could be used in phytoremediation ofmetal (Al) contaminated soils.