The effect of arbuscular mycorrhizal inoculation and plant growth-promoting rhizobacteria on maize (Zea mays L.) under boron toxicity stress

A greenhouse study was conducted to investigate the effect of arbuscular mycorrhiza fungus and plant growth-promoting rhizobacteria on maize (Zea mays L.) yield and boron (B) uptake under excessive B concentrations. Four levels of B (0, 10, 20 and 40 mg kg-1 soil) and four levels of microbial inoculation (non-inoculation, Rhizophagus intraradices, Micrococcus yunnanensis and co-inoculation) were applied. In general, elevated B decreased the maize relative yield, plant dry weight, plant height, total leaf area and chlorophyll content. The highest B uptake was recorded in the 20 mg kg-1 B treatments, whereas the lowest uptake was in B treatments of 0 and 40 mg B kg-1. Excessive B supply increased the proline content and electrolyte leakage of maize leaves. Microbial inoculation did not change the yield of B-stressed plants. In addition, mycorrhiza inoculation and co-inoculation increased the shoot and root B uptake. Maize plants growing at high B concentrations with or without microbial inoculation showed leaf edge burning and necrosis when compared with control treatments. Microbial inoculation improved the maize yield under B stress up to 20 mg B kg-1. Thus, inoculation with arbuscular mycorrhiza and plant growth promoting rhizobacteria can increase the maize tolerance under B toxicity. Nonetheless, the inoculation of bacterium and arbuscular mycorrhiza had a more alleviative effect when the plants were exposed to excess B.