PATTERNS IN SELFED SEED PRODUCTION AND GERMINATION IN AMUR HONEYSUCKLE (LONICERA MAACKII)

Abstract

Amur honeysuckle (Lonicera maackii) is an aggressive invader of forests throughout the eastern United States. While self-pollination has been identified as an important trait of invasive plant species, this trait is understudied, and Amur honeysuckle is anecdotally described as lacking this characteristic. To examine the ability of Amur honeysuckle to self-pollinate, we selected 171 individual shrubs distributed across nine sites. Each site was grouped into one of three invasion types: heavy, light, and sprouting (sites on which a basal cutting treatment previously occurred, but Amur honeysuckle was allowed to reestablish). We compared the number of berries, seeds per berry, and seed germination rates of self- and open-pollinated flowers by pairing branches covered with pollination bags prior to flower emergence with uncovered branches on the same individual shrub. Out of 171 individuals, 48 produced berries from self-pollination within pollination bags (28%), with 48% of bagged branches exhibiting some degree of necrosis or chlorosis, presumably due to increased temperature and humidity. Berries from self-pollination produced 1.5 ± 1.4 (mean ± 1 SD) seeds per berry, whereas berries resulting from open-pollination produced 3.3 ± 1.5 seeds per berry. In a germination trial, 47.3% of self-pollinated seeds germinated, compared to 41.7% of open-pollinated seeds. This study has shown that Amur honeysuckle can self-pollinate and set viable seed, providing the species with an important mechanism to increase population abundance during the early stages of invasion.