Effect of Different Size Silver Nanoparticles Synthesized at Varying pH of Plant Extract for Germination Improvement of Tetraploid Watermelon (Citrullus lanatus)

Abstract

Silver nanoparticles synthesized through green methodologies can offer a low-cost, reproducible, and environmentally sustainable solution for enhancing seed germination and antibacterial activity. In the present study, varying sizes of silver nanoparticles (AgNPs) were synthesized using Neem (Azadirachta indica) leaves aqueous plant extract at varying pH (5.7, 7, 8.5 and 10) and a 2.5% AgNPs solution (26.54, 30.36, 27.88 and 26.73 ppm), respectively, were applied to low germinating tetraploid seeds of watermelon (Citrullus lanatus). The AgNPs were characterized by UV-Visible spectrophotometer resulted blue-shift of spectra as the pH increased, Dynamic light scattering confirmed decreased in size of nanoparticles as the pH increased, Transmission electron microscopy and Scanning electron microscopy analysis confirmed the spherical nature of AgNPs, and the presence of functional groups confirmed by Fourier transform infrared spectroscopy and Raman spectroscopy. However, average size of 51.75 nm at pH 8.5 gave 83% increase in germination, and 70% improvement with average size of 142.8 nm at pH 5.7 for tetraploid (KSP-13379) compared to untreated. A similar increase for diploid varieties (KSP-1127 and BSS-586) observed by 21.6% and 44.5% compared to untreated seeds. The highest germination percentages of 100%, 86.67% and 95.56% were obtained with AgNP (pH 8.5) nanoprimed compared to untreated 82.22%, 60% and 52.22% varieties of KSP-1127, BSS-586 and KSP-13379 respectively, at 21 days. The size of AgNPs synthesized at pH 8.5 is highly suitable for seed germination, germination index, vigor index and plant length of tetraploid and diploid varieties. Hence, the results indicate that AgNPs nanopriming at varying pH levels yields beneficial effects by producing nanoparticles of diverse sizes, thereby improving germination percentage, germination rate, and seedling length.