Seed storage reduces the optimal temperature for germination of wild castor seed accessions

Castor plant ( Ricinus communis L.) is a non-edible raw material of importance for several industries, including cosmetics, pharmaceuticals, and energy. However, its commercial production is limited by seed dormancy, which affects germination rate and germination temperature under field conditions. In this study, the germination and cardinal temperatures (base temperature, optimal temperature, and critical temperature) of four accessions collected from the Mediterranean-climate areas in the Metropolitana and Valparaíso regions of Chile, were evaluated. Overall, fresh seeds showed lower germination than seeds stored for 6 or 12 months prior to germination. In addition, seed storage modified the cardinal temperatures, thereby extending the temperature range suitable for germination. Notably, fresh seeds of one specific accession (H40) exhibited a higher germination even without storage, indicating substantial variability in germination behavior among wild castor accessions collected under Mediterranean conditions. Nevertheless, further evaluation of additional agronomic and quality-related traits, such as seed yield, dehiscence, and seed oil content, is required.