Root plant growth promoting rhizobacteria inoculations increase ferric chelate reductase (FC-R) activity and Fe nutrition in pear under calcareous soil conditions

Abstract

Iron deficiency occurring in calcareous soil is a problem in various plants. It is well known that some soil bacteria can release organic acids that can decrease the pH of the soil rhizosphere. However, there have been no attempts to study the effects of plant growth promoting rhizobacteria (PGPR), including organic acid releasing bacteria, on the organic acid contents of the leaf and FC-R activity in the roots and leaves under calcareous soil conditions. Therefore, pear plants were inoculated with 6 bacterial strains with the aim of acquiring iron under calcareous conditions. Uniform 1-year-old pear cv. Deveci sapling grafted on BA-29 and OHF-333 rootstocks were planted in plastic pots containing 10L of loamy soil at 29.6% CaCO3. All bacteria were applied to the roots as an inoculation before planting. The root and leaf Fe content, FC-R activity, leaf organic acids, and soil Fe content were compared in the Alcaligenes 637Ca, Agrobacterium A18, Staphylococcus MFDCa1, MFDCa2, Bacillus M3 and Pantoea FF1 strains. The study showed that the leaf organic acid content and the Fe content in the soil, root and leaf were significantly affected by the bacterial treatments in pear plants. It was determined that the total and active Fe in the leaf was higher in OHF-333 compared to BA-29 by 7% and 14%, respectively. Furthermore, the leaf FC-R activity of Deveci on OHF-333 was 8% higher than that on BA-29. In the Deveci/BA-29 plants, the 637Ca treatment had the highest root FC-R activity value (107nmolFe+2gr−1FW h−2). The highest leaf FC-R activity value was obtained from the MFDCa1, MFDCa2 and FF1 treatments (58.4, 56.3 and 55.7nmolFe+2gr−1FWh−2, respectively). The bacterial strains used in the present study have an important potential to be used as a biofertilizer to replace the use of iron fertilizers.