Studies on improvement in growth, yield and antioxidant content in sugarbeet (Beta vulgaris L.) by application of plant growth promoting microbial inoculants and consortia.

Sugarbeet (Beta vulgaris L.), a tuberous root crop from the Chenopodiaceae family, exhibits significant tolerance to salinity. One of its key bioactive compounds, betanin, is a type of betalain, which is known for its potent antioxidant properties. Betanin plays a crucial role in mitigating the ageing process by protecting cells against oxidative stress and damage induced by free radicals. In the present study, beet root was cultivated under saline soil conditions (pH- 8.1, EC- 5.42 dS/m) on experimental field at Babasaheb Bhimrao Ambedkar University, India in a randomized block design (RBD) for two subsequent years from November 2021 to February 2022 and November 2022 to February 2023. The experimental treatments included the application of plant growth-promoting microbes, such as Bacillus filamentosus, Bacillus firmus, Aspergillus tamari, Aspergillus terreus, Aspergillus luchensis and Trichoderma lixii, which were also tested for their compatibility. These microbes were firstly immobilised in organic amendments (bentonite, pressmud and molasses) and then applied twice in the field at the time of seed sowing and after a month of seed sowing in the soil, to compare with a control without any microbial or chemical treatments. The betanin content in beet-root extracts was quantified using high-performance liquid chromatography (HPLC) following the application of the various microbial and fungal treatments. The results indicated that microbial treatments, particularly the bacterial treatments of B. filamentosus and B. firmus as well as the fungal treatment of T. lixii, significantly increased betanin content as compared to the control. Moreover, the plants treated with consortia of B. filamentosus + B. firmus, A. luchensis + T. lixxi and B. filamentosus + T. lixxi exhibited higher percent increase in anthocyanins than the untreated control plants. Among the consortia, B. filamentosus + T. lixxi showed best results in terms of growth, productivity and metabolite concentration. Additionally, the application of microbial bioinoculants as consortia, resulted in notable improvements in root length and root girth, as well as overall yield. Other than this, application of such microbial inoculants improved the properties of saline soil like pH, EC, total nitrogen and total phosphorus. These treatments not only enhanced growth parameters but also contributed to a significant increase in biomass. Based on these findings, it is concluded that microbial and fungal inoculants can substantially enhance the growth, yield and antioxidant content (such as betanin and anthocyanins) while also strengthened antioxidant defence mechanisms by reducing oxidative stress indicators like H₂O₂ and lipid peroxidation of beet-root crop. Therefore, the use of such microbial treatments is recommended for improving quality and quantity of beet-root under saline conditions.