Cassidy L. Sharpe

Soybean [Glycine max (L.) Merr.] productivity is often limited by abiotic stresses such as drought, heat, and suboptimal temperatures during germination and early establishment. Protein hydrolysates (PHs) are biostimulants that can improve crop stress resilience, but whether foliar PH application to parental plants influences untreated F1 progeny seed performance remains poorly understood. This study evaluated whether parental foliar application of three PHs differing in amino acid composition (EZGro 16-0-0, EZGro 18-0-0, and iQForte), an equal-N foliar urea comparator, or a base-fertilizer/no-foliar control altered progeny germination, seedling vigor, and stress responses. Progeny seeds were tested using AOSA rolled-towel germination assays and controlled-environment phytotron assays under drought and temperature stress. Responses were composition-dependent and stress-specific. EZGro 16-0-0 produced PH-specific positive responses for 2023 AOSA germination, vigor index, and root length, and for 2024 root:shoot ratio. EZGro 18-0-0 produced PH-specific responses for germination in both years and for selected dry-matter traits. iQForte produced a PH-specific response for germination under well-watered phytotron conditions. Several additional responses were greater than urea only. These findings indicate that parental foliar PH application can alter selected progeny seedling traits in product-specific and environment-dependent manners, but the underlying biochemical or epigenetic mechanisms require further identification.