Iron effect on symbiotic efficiency of horse gram

Abstract

Four horse gram Rhizobium (HGR) strains HGR-4, 6, 13 and 25 grown under different concentrations of Iron (Fe) were inoculated individually to horse gram plants. These plant sets were screened for their net photosynthetic rate (P_N), pod formation and symbiotic efficiency. Horse gram plants inoculated with the strain HGR-4 have shown high P_N values at 100 µg g^-1 of Fe. The number of pods formed were maximum upon inoculation with HGR-4 at 300 µg g^-1 of Fe. Nodulation was maximum with the prior inoculation of the strains HGR-6, 13 and 25 at 500 µg g^-1 of Fe. Leghaemoglobin content was maximum on inoculation with HGR-6, 13 and 25 at 300 µg g^-1 of Fe. This study demonstrated that the horse gram plants associated with rhizobia, besides having nitrogen fixing capacity also have shown Fe stress tolerance and the ability to remove Fe from soils. Hence, the study confirms the ability of HGR-4, HGR-6, HGR-13 and HGR-25 isolates of Rhizobium to have tolerance of the metal Fe at the plant nodule during pot experiments. Therefore these isolates could be suggested for cultivation of horse gram plants in Fe contaminated soils. These findings imply that horse gram-rhizobia symbiosis is an essential element of plant adaptation to metal stress.

Key words: Iron, rhizobia, metal tolerance, symbiotic efficiency