Search

We determined the requirements for dormancy break/germination and kind of dormancy in seeds of the Hawaiian lobelioids Cyanea kunthiana, Delissea rhytidoperma, Lobelia grayana, L. hypoleuca, Trematolobelia grandifolia, and T. singularis. Fresh seeds were incubated in light/dark at 15/6, 20/10, and 25/15 [degrees]C, and germination monitored at two-week intervals for 14 weeks. For each species, the mean embryo length (E): seed (S) length ratio was determined for freshly matured seeds and for seeds at the time the seed coat split but before radicle emergence (germination). The embryo in seeds of all six species incubated at 25/15 [degrees]C grew inside the seed prior to germination (42%-148% increase in E:S ratio, depending on species). Seeds of L. grayana and L. hypoleuca have morphological dormancy (MD); they germinated to 82%-98% at the three temperature regimes in 4 weeks. Seeds of the other species have nondeep simple morphophysiological dormancy (MPD) and require >4 weeks for maximum germination to occur. Our results add to the growing body of knowledge about the kind (class) of seed dormancy in Campanulaceae, which suggests that seeds of members of this family have either MD or MPD and embryos grow at warm ([greater than or equal to]15 [degrees]C) temperatures. Key words: embryo growth, endemic species, morphological dormancy, morphophysiological dormancy, seed dormancy. Les auteurs ont déterminé les conditions de rupture de la dormance/germination et le type dormance de graines des lobélioïdes d'Hawai'i Cyanea kunthiana, Delissea rhytidoperma, Lobelia grayana, L. hypoleuca, Termatolobelia grandifolia et T. singularis. Des graines fraîches ont été incubées à la lumière/obscurité à 15[degrees]/6[degrees], 20[degrees]/10[degrees] et 25[degrees]/15 [degrees]C et la germination a été suivie toutes les deux semaines pendant 14 semaines. Pour chaque espèce, le rapport de la longueur moyenne de l'embryon (E) : longueur moyenne de la graine (S) a été déterminé pour les graines fraîchement mûres et pour les graines au moment de l'ouverture du tégument, mais avant l'émergence de la radicelle (germination). L'embryon des graines des six espèces incubées à 25[degrees]/15 [degrees]C se développait à l'intérieur de la graine avant la germination (augmentation du rapport E : S de 42 à 148% selon l'espèce). Les graines de L. grayana et de L. hypoleuca ont une dormance morphologique; elles germaient à 82-98% aux trois régimes de températures en 4semaines. Les graines des autres espèces ont une dormance morphophysiologique simple non profonde et nécessitent plus de 4 semaines pour que la germination soit maximale. Ces résultats ajoutent au corpus croissant des connaissances sur le type (classe) de dormance des graines chez les Campanulaceae, ce qui suggère que les graines des membres de cette famille ont soit une dormance morphologiqueouune dormance morphophysiologique, et que les embryons se développement à des températures chaudes ([greater than or equal to] 15 [degrees]C). [Traduit par la Rédaction] Mots-clés : croissance des embryons, espèces endémiques, dormance morphologique, dormance morphophysiologique, dormance des graines., Introduction The eudicot family Campanulaceae (APG IV 2016) consists of herbaceous annuals, biennials, and perennials and includes pachycaul rosette plants, subshrubs, shrubs, treelets, trees to 15 m tall (Lammers 2007), [...]

Worldwide, there is relatively little information on seed dormancy and germination of tropical montane species. Our aim was to help fill this knowledge gap by conducting seed dormancy/germination studies on woody species from this vegetation zone in Hawai'i. All species had water‐permeable seeds with a fully developed embryo. Seeds of 29 species (23 genera) were incubated in light/dark at 15/6, 20/10 and 25/15°C and germination monitored at 2‐week intervals for 16–128 weeks. Seeds of Chenopodium oahuense, Dubautia menziesii and Silene lanceolata were non‐dormant (ND) and those of 26 other species had physiological dormancy (PD); 10 of the 26 species had conditional PD. The optimum germination temperature regime(s) was (were) 25/15°C, 17 species; 25/10 and 20/10°C, 2; 20/10°C, 6; 20/10 and 15/6°C, 2; and 15/6°C, 2. Worldwide, PD in the woody genera included in our study is more common than ND. In addition to its contribution to the world biogeography of seed dormancy/germination, this study will be useful to conservation biologists who need to germinate seeds of tropical montane species. [ABSTRACT FROM AUTHOR]