Seed dormancy and germination of the endangered exceptional Hawaiian lobelioid Brighamia rockii

Abstract

Premise The Campanulaceae (Lobelioideae) is the Hawaiian plant family with the most endangered and extinct species. Although seeds of Hawaiian lobelioids are desiccation tolerant, the species are exceptional (i.e., they present challenges at various stages of the conventional ex situ conservation chain) due to their generally poor seed survival at the conventional seed‐banking temperature (–18°C). Both morphological dormancy (MD) and morphophysiological dormancy (MPD) have been identified in the seeds of other Hawaiian lobelioids; however, the class of dormancy and germination requirements of the Critically Endangered genus Brighamia have not yet been determined. Methods We measured the embryonic growth in 12‐week‐old seeds of B. rockii and tested their germination at three temperature regimes (15/5°C, 20/10°C, and 25/15°C) in light and at 25/15°C in darkness. Results The embryos grew prior to radicle emergence, and the seeds germinated rapidly to high percentages in all tested conditions. Discussion Whether fresh B. rockii seeds have MD or MPD still needs to be determined; nevertheless, 12‐week‐old seeds germinated well in light and darkness, and thus the seeds can be used for conservation purposes. Germination in the dark suggests that the species may not form a long‐lived soil seed bank in its native habitat.

Dormancy-release and germination improvement of Korean bellflower (Campanula takesimana Nakai), a rare and endemic plant native to the Korean peninsula

“…Similar to other Campanulaceae families, the seeds of the native Korean C . takesimana species had underdeveloped embryos from their parent plants at the time of dispersal and showed MD that required embryo development before germination [ 13 , 14 ]. Before radicle protrusion, the E:S ratio increased from 0.40 to 0.67, and the cumulative germination did not reach 36.00% within 30 d in the temperature regime groups.…”

“…From the perspective of forest restoration, it is necessary to not only understand the ecology of wild plants but also understand the propagation method of seeds with high genetic diversity for restoration [ 13 ]. Thus, regardless of seed source, species-specific knowledge of dormancy-release and germination requirements is needed for the successful cultivation of plants from seeds for application in different industries [ 14 ].…”

“…Based on previous studies of seeds of species of Campanulaceae, we hypothesized that C. takesimana seeds would have one of the four dormant classes: ND, MD, PD, and MPD [13,14,[27][28][29]. To test our hypothesis, we investigated the (1) constant and fluctuating temperature regimes required to improve germination percentage, (2) morphology of embryo growth and seed germination under laboratory conditions, and (3) effects of cold stratification and GA 3 on dormancy-release.…”

Building capacity in the conservation of exceptional plant species

“…For many species, exceptional or not, seed germination requirements are poorly understood or unknown. Wolkis et al ( 2022 ) address this issue with the exceptional species Brighamia rockii H. St. John by investigating dormancy and germination requirements. Using a systematic approach to uncovering germination requirements not only informs best practices for the conservation of the species but allows researchers to make inferences on the longevity of seed viability in both the seed bank and the wild.…”

Supporting long‐term sustainability of ex situ collections using a pedigree‐based population management approach

“…For this reason, the species is classified as exceptional under exceptionality factor 3 (EF3; Pence et al, 2022 ). A recent seed dormancy and germination study of the only other species in the genus, B. rockii H. St. John, found that seeds are able to germinate in darkness, suggesting the species is unlikely to form a long‐lived soil seed bank (Wolkis et al, 2022 ). If we assume B. insignis seeds behave similarly, these findings further support the notion that reintroductions will be needed to reestablish extirpated populations.…”