The effects of freezing and stratification on pecan (Carya illinoinensis) seed germination and seedling growth

Pecan (Carya illinoinensis) cultivation is crucial for commercial production and relies on selecting rootstocks adapted to local environments. Historically, pecan breeding has prioritized scion improvement over rootstock selection due to propagation challenges. However, rootstocks significantly impact scion growth, phenology, and productivity. Pecan nurseries use open-pollinated seeds from regionally favored cultivars (seedstocks) as rootstocks, and seedstock influences germination. Challenges arise from seed dormancy, with some varieties stratification or having thick shells, which affect germination and seedling growth. Pecan nurseries use freezing to eliminate pecan weevil infestations and stratification to synchronize seed germination, but their effects are not well quantified. This study investigates how freezing and stratification impact seed germination and seedling growth across 12 pecan seedstocks from diverse origins. Results indicate that both freezing and stratification, or their combination significantly affect seed germination. Stratification improved germination rates, with non-stratified frozen seeds averaging only 15.7% compared to 48.5% for stratified seeds. Stratified seeds also emerged faster, averaging 18 d, whereas non-stratified seeds took 37 d. The effect of stratification on germination was not influenced by freezing. Although freezing reduced germination rates, especially when combined with stratification, seedstock origins did not significantly affect germination. Stratification interacted significantly with northern and southern origins. The study underscores the need for a nuanced approach to seed treatment. While stratification is crucial for enhancing germination and seedling growth, freezing treatments should be optimized to balance pest control with seed viability. Future research should focus on refining these treatments to minimize their negative impacts.