Investigations into Selected Pollinator-Friendly Plant Species: Seed Lot Germination, Breaking Dormancy with Plant Hormone Priming and the Influence of Water Stress on Germination

The lack of protocols for breaking seed dormancy, inconsistent seed quality, and abiotic stress factors such as drought impede large-scale restoration efforts of pollinator-friendly native plant species. This research explores the germination response, dormancy-breaking techniques, and water stress tolerance in selected pollinator-friendly plant species with characteristics facilitating mechanized rehabilitation protocols and biodiversity enhancement. Forty-two commercial seed lots representing seven plant families with 28 species were evaluated under two alternating temperature regimes (15/25 °C and 20/30 °C) with and without gibberellic acid (GA₃) priming treatments. Six of the twenty-eight species were selected based on pollinator requirements for the monarch butterfly (Danaus plexippus L.) and further examined by priming seeds for 24 h in solutions containing GA₃, kinetin (KIN), and hydrogen peroxide (H₂O₂), or their combinations, to evaluate their dormancy-breaking responses. The effect of water stress on seed germination was assessed in controlled chambers at soil water potentials of −1.08, −0.75, −0.13, and 0 MPa. Initial seed quality of the 42 seed lots revealed that only 62% had greater than 50% germination, while of the same 42 lots, 98% had greater than 50% viability based on the commercial seed label. The difference was largely attributed to seed dormancy. In laboratory studies of the 42 seed lots, GA₃ significantly enhanced germination percentage, and reduced T₅₀ (time to 50% germination) across most seed lots. Overall, germination was higher and faster at 20/30 °C than 15/25 °C. Priming the six selected species with 1.0 mM GA₃ in 0.3% H₂O₂ consistently improved germination compared to the non-primed control after 14 days. Asclepias species (A. incarnata, A. syriaca, and A. tuberosa) exhibited consistently high germination across a broad moisture range of −0.75 to 0 MPa. In contrast, Echinacea purpurea required high moisture levels (−0.13 to 0 MPa) for optimal germination. Monarda fistulosa and Rudbeckia hirta showed their best performance under moderate moisture conditions (−0.13 MPa). Collectively, the use of GA₃ priming to break physiological seed dormancy offers a promising approach to enhance germination and improving the establishment potential of native pollinator species in restoration programs.