Independent Effects of Seed-Priming Treatments and Seed Mass Class on Germination and Early Seedling Performance of Silphium perfoliatum L.

Silphium perfoliatum L. is a promising perennial bioenergy and forage crop; however, its agricultural expansion is severely hindered by primary physiological dormancy and non- uniform seedling emergence This study evaluated the effects of chemical priming treatments (distilled H2O, H2O2, GA3, KNO3, ethephon, and sodium nitrophenolate (SNP)) and the seed mass classification (small: 0.011–0.015 g; medium: 0.016–0.019 g; large: 0.020–0.024 g) on germination dynamics, allometry, and seedling vigor. Under controlled conditions, priming agents demonstrated highly differentiated morpho-regulatory capacities. Gibberellic acid (GA3) significantly overcame physiological dormancy, maximizing the final germination percentage (77.33%), germination index (2.54), and seedling vigor index II (SV II) (4.62) compared to the control (23.33%, 0.99, and 1.11, respectively). Conversely, KNO3 and ethephon optimized germination synchrony (Z) (0.27 and 0.29) and suppressed early fragile shoot etiolation to enhance dry matter accumulation (0.064 g). Furthermore, multivariate morphometric analysis of seed mass categories revealed a distinct transverse allometric expansion in larger seeds (length-to-width ratio decreasing from 1.58 in small seeds to 1.50 in large seeds). While the ultimate germination capacity remained statistically unaffected by seed size (37.60% to 47.20%), large seeds exhibited a pronounced early kinetic divergence, achieving a developmental head start (23.2% cumulative germination by day 8 versus (7.2%) for small seeds. Larger seed mass directly translated into superior structural biomass accumulation, yielding significantly robust seedlings with elevated fresh weight (1.059 g vs. 0.789 g in small seeds), dry weight (0.073 g vs. 0.041 g), and total seedling length (91.32 mm vs. 73.70 mm), without altering the radicle-to-shoot allocation ratio (0.89 vs. 0.76). We conclude that early crop establishment in S. perfoliatum is driven by dormancy-breaking chemical signaling and reserve-dependent physical seed quality.