The Potential Utilization of Mycorrhizal Fungi and Glycine Betaine to Boost the Fenugreek (Trigonella foenum-graecum L.) Tolerance to Chromium Toxicity

Chromium (Cr) is one of heavy metals that extremely dangerous to the ecosystem, especially plants as it has a detrimental influence on numerous physiological and metabolic pathways, which in turn affects the plant growth, development, and nutrient-taking capacity. The application of arbuscular mycorrhizal (AM) fungi or glycine betaine (GB) was widely studied regarding their potential to alleviate Cr toxicity. However, limited information is documented regarding their combined use. A greenhouse experiment was conducted to study the ameliorative effects of AM application and GB (50 mM) foliar spray either individually or in combination on fenugreek (Trigonella foenum-graecum L.) plants upon 200 mg kg-1 Cr stress. Results showed that the separate application of AM and GB markedly alleviated Cr toxicity on shoot height, root length, total fresh and dry weights and Cr-stress indices of fenugreek plants, with a more obvious alleviation with their dual applications. A significant increase in total chlorophyll (32.31, 14.51 and 44.06%) validated the effectiveness of AM, 50 mM GB and AM + GB in Cr-stressed plants as compared to stressed one. Cr stress significantly increased arbuscules colonization in the roots of trigonella by 43.16%. The extraordinary result was that 200 mg kg-1 of Cr increased mycorrhizal dependency of trigonella plants (120.40%) compared to those that were not stressed (73.16%). The combined application of AM fungi and GB markedly reduced Cr-induced malondialdehyde, and increased the total Chl, growth attributes, proline, protein, free amino acids and sugars as compared to their respective controls. AM colonization with GB counteracted Cr-induced alterations of peroxidase and ascorbate peroxidase activities in fenugreek shoots. These findings demonstrated that, in comparison to their individual applications, the combination use of AM and GB is more effective and will provide novel perspectives for reducing Cr toxicity, and will boost plant tolerance.