Effect of Preserved Compost Tea Microbial Isolates on the Growth Performance of Mustard Plants

Compost tea contains a diverse consortium of beneficial microorganisms that enhance plant growth and soil health, yet its use is often limited by the rapid decline in microbial viability during storage. This study aimed to overcome this limitation by isolating compost tea microorganisms and evaluating two preservation strategies—freeze-drying and cold storage—to maintain long-term microbial activity. Microbial cultures harvested at the 12th hour of the exponential phase exhibited the highest post-rehydration viability after freeze-drying (1000 CFU/mL), confirming the superior stability of this method compared to cold storage at 4 °C. The preserved microorganisms were subsequently reactivated and applied to mustard (Brassica juncea) to assess their growth-promoting effects. Mustard plants treated with 30%, 50%, and 70% formulations demonstrated higher growth rates of 0.0043, 0.0037, and 0.0070 day⁻1, respectively, compared to 0.0021 day⁻1 in the untreated control, indicating enhanced plant performance associated with microbial inoculation. Overall, the findings highlight the effectiveness of freeze-drying as a preservation technique for maintaining compost tea microbial isolates and support their potential use as a stable, sustainable bio-stimulant for crop production.