Abstract Description

Low temperatures caused by climate change negatively affect agricultural productivity by inhibiting microbial activity essential for plant growth. Although, bacteria such as Serratia marcescens (SM) have proven to thrive at low temperatures (psychrotolerant) and acts as bio-stimulants, there are insufficient studies on their effectiveness to maximize their plant growth-promoting (PGP) potential under cold-stressed environments. Nanoparticles (NP) have also shown the potential to enhance plant performance under stress conditions; however, their combined effect with psychrotolerant, PGP microbes under cold stress remains underexplored. Therefore, the study aimed to evaluate the effects of calcium phosphate (CaP) and iron oxide (IO) NP as well as SM on the germination of tomato (Solanum lycopersicum) seeds under controlled, cold stressed conditions. Tomato seeds were surface sterilized and primed with SM culture at 1 x 108 CFU/mL, CaP and IO NP at two concentrations (25 and 50 mg/L), and their combinations (nano-biopriming). Seed viability was confirmed by flotation prior to sterilization. Seed priming was conducted with agitation at 25 °C followed by germination in the dark at 15 °C for 10 days on moistened filter paper. Germination parameters including germination rate, vigour index, seedling root, shoot, and total length were recorded. The seed priming treatments investigated in this study demonstrated substantial enhancements in tomato seedling growth under cold stress conditions (15 °C). Specifically, treatments involving nano-biopriming with SM combined with CaP and IO NP markedly improved seedling performance compared to the hydroprimed control. The SM + 50 mg/L IO NP (SF50) treatment yielded the longest roots at 51.05 mm, representing nearly a twofold increase relative to the control root length of 27.21 mm. Similarly, the SM + 50 mg/L CaP + 50 mg/L IO NP (SCF50) treatment significantly increased root length to 43.57 mm and shoot length to 10.31 mm, both substantially higher than control measurements of 27.21 mm and 4.98 mm, respectively. Enhanced root to shoot ratios observed in the SF50 (6.79) and SCF50 (5.20) treatments, relative to the control ratio of 5.95, indicate a shift in biomass allocation in response to different treatment. These findings suggest that nano-biopriming enhances seed germination and seedling vigour, highlighting the potential of bacterial NP synergistic applications to improve crop establishment under cold stress.