The great diversity in kinds of seed dormancy: a revision of the Nikolaeva–Baskin classification system for primary seed dormancy

This review provides a revised and expanded word-formula system of whole-seed primary dormancy classification that integrates the scheme of Nikolaeva with that of Baskin and Baskin. Notable changes include the following. (1) The number of named tiers (layers) in the classification hierarchy is increased from three to seven. (2) Formulae are provided for the known kinds of dormancy. (3) Seven subclasses of class morphological dormancy are designated: ‘dust seeds’ of mycoheterotrophs, holoparasites and autotrophs; diaspores of palms; and seeds with cryptogeal germination are new to the system. (4) Level non-deep physiological dormancy (PD) has been divided into two sublevels, each containing three types, and Type 6 is new to the system. (5) Subclass epicotyl PD with two levels, each with three types, has been added to class PD. (6) Level deep (regular) PD is divided into two types. (7) The simple and complex levels of class morphophysiological dormancy (MPD) have been expanded to 12 subclasses, 24 levels and 16 types. (8) Level non-deep simple epicotyl MPD with four types is added to the system. (9) Level deep simple regular epicotyl MPD is divided into four types. (10) Level deep simple double MPD is divided into two types. (11) Seeds with a water-impermeable seed coat in which the embryo-haustorium grows after germination (Canna) has been added to the class combinational dormancy. The hierarchical division of primary seed dormancy into many distinct categories highlights its great diversity and complexity at the whole-seed level, which can be expressed most accurately by dormancy formulae.

Techniques for breaking seed dormancy of rainforest species from genus Acronychia

We tested for dormancy in three species of Acronychia (Rutaceae) occurring in the rainforest in eastern Australia, A. imperforata, A. laevis and A. oblongifolia, by incubating fresh intact seeds on 0.8% water agar for one month at 25/10°C. Four different techniques were then tested for their effect on dormancy: (i) incubation of intact seeds on agar incorporating gibberellic acid (GA3); (ii) seed coat removal (decoating); (iii) scarification near the radicle emergence point (scarification-emergence point); and (iv) scarification opposite the radicle emergence point (scarification-back). Imbibition tests were performed to determine whether dormancy was due to an impermeable seed coat. Germination differed among treatments, but all three species showed a similar pattern. Intact seeds showed < 6% germination after one month indicating the presence of dormancy. Highest germination (> 65%) was observed following scarification-emergence point treatment. Seed coat removal also resulted in increased germination (40-47%), in comparison with intact seeds, but GA3 and scarification-back treatments did not (< 12%). Though the seedcoats of all species were permeable, increased germination responses to decoating and scarification-emergence point treatments suggest scarification is required to clear the radicle emergence point. This may be a useful dormancy-breaking technique for Acronychia spp. and may be suitable for related Rutaceae species.

Breaking seed dormancy of Astragalus penduliflorus Lam.

<em>Astragalus penduliflorus</em> Lam. is an alpine-subalpine species. Several isolated populations occur in Europe: in the Alps, Pyrenees, Carpathians and in central Sweden. <em>Astragalus penduliflorus</em> is considered as critically endangered species in Poland, growing only at the locality in the Smytnia Valley, in the Western Tatra Mountains. The population is at risk, due to the limited reproduction caused by law rate of seed germination, periodically shortened vegetation period that prevent seed development and gnawing the aerial plant parts by deer. The aim of the study was to explain the reason for the poor germination of <em>A. penduliflorus</em> seeds. As a result of mechanical scarification, 100% of <em>A. penduliflorus</em> seeds germinated, which proved that these seeds are characterized by a water-impermeable seed coat, which classified them as hard seeds that go through physical dormancy. Results obtained in this work can be used for effective reproduction and active conservation of threatened <em>A. penduliflorus</em>.

A new seed coat water-impermeability mechanism in Chaetostoma armatum (Melastomataceae): evolutionary and biogeographical implications of physiophysical dormancy

Determining the phylogenetic and biogeographic distribution of physical dormancy remains a major challenge in germination ecology. Here, our goal was to describe a novel water-impermeable seed coat mechanism causing physical dormancy (PY) in the seeds of Chaetostoma armatum (Melastomataceae). Although seed coat permeability tests indicated a significant increase in seed weight after soaking in distilled water, anatomical and dye-tracking analyses showed that both water and dyes penetrated the seed coat but not the embryo, which remained in a dry state. The water and dye penetrated the lumen of the exotestal cells, which have a thin outer periclinal face and thickened secondary walls with U-shaped phenolic compounds. Because of this structure, water and dye do not penetrate the inner periclinal face of the exotestal cells, indicating PY. Puncturing the seeds increased germination more than tenfold compared to that of the control, but GA3 did not increase germination further. A significant fraction of the seeds did not germinate after puncturing, indicating that embryos are also physiologically dormant (PD). This paper constitutes the first report of the water-impermeable seed coat in the Myrtales and the first report of physiophysical (PD+PY) dormancy in a shrub from a tropical montane area.

Vegetative Propagation Studies in Myrica esculenta (Kafal) - A Non-Legume Nitrogen Fixing Species

Myrica esculenta is a wild nitrogen fixing tree, growing naturally in the forest edges at high elevation rain fed areas. This species is generally propagated via seeds but physical dormancy caused by impermeable seed coat causes an unreliable germination pattern. In the present study different types of cuttings were collected and planted in an open side area at Khirsu as well as in mist chamber after treating with different hormonal (IBA) doses i.e. 1000 ppm; 2000 ppm; 4000 ppm; 6000 ppm and one set was soaked in water and kept as control. No rooting was observed from any type of cutting however, only few cuttings at 4000 ppm IBA treatment in the June month were sprouted and died after three weeks of transplanting. In case of air layering, maximum roots were sprouted in the air layered treatments done during post summer or rainy season whereas, air layered done during winter season or pre summer season, no response was observed. Maximum (15.83%) rooting was recorded in the 4000 ppm IBA followed by 6000 ppm (9.17%), 2000 ppm (6.67%) and minimum in 1000 ppm (4.17%) treatments. In this study overall 7.17 per cent rooting was recorded in first year and 1.67 per cent in second year. The air layering done in the VMG at Dehradun all air layered branches except control showed rooting and better performance was recorded in 4000 ppm IBA than other. Both seed and air layered raised plants when planted in the field their growth and survival percentage was almost similar.

Are wildfires an adapted ecological cue breaking physical dormancy in the Mediterranean basin?

Many studies have claimed that fire acts as the chief ecological factor cueing dormancy break in seeds with a water-impermeable seed coat, i.e. physical dormancy (PY), in Mediterranean ecosystems. However, a proposal is made that seasonal temperature changes must be viewed as more meaningful dormancy-breaking cues because: (1) fire is erratic and may break PY in seasons during which seedlings cannot complete their life cycle; (2) fire may not occur for long periods, thereby only providing an opportunity for dormancy break and germination once in every several years; and (3) if fire opens the specialized anatomical structures called ‘water gaps’, in seconds, their evolutionary role of detecting environmental conditions becomes irrational. Although fire breaks dormancy in a proportion of seeds, given the risk of seed mortality and the post-fire environment providing cues for dormancy break, it is suggested that fire might possibly be an exaptation.

Carbohydrate mobilisation in germinating seed of Enterolobium contortisiliquum and Peltophorum dubium (Fabaceae), two tropical trees used for restoration

Enterolobium contortisiliquum (Vell.) Morong. and Peltophorum dubium (Spreng.) are two leguminous species native to Brazil that are frequently used to restore degraded areas. Seed of E. contortisiliquum are exalbuminous, whereas seed of P. dubium have a mucilaginous endosperm and both are orthodox, dormant and have a water-impermeable seed coat. There is little information about the dynamics of their germination and understanding this process is important for propagation, conservation and satisfactory practices for restoration of degraded areas. Thus, in this study we evaluated and compared the carbohydrate mobilisation of the seed of both species during germination and early seedling development. Data obtained showed differences in the composition and in the mobilisation of the storage carbohydrates in the studied species. Whereas the main storage of the E. contortisiliquum embryo is starch, the main reserve found in P. dubium is the galactomannan stored in the endosperm. The carbohydrates first hydrolysed in both species are raffinose family oligosaccharides that are used in the embryo development during germination. Starch found in cotyledons of E. contortisiliquum or accumulated after galactomannan degradation in the embryo of P. dubium is not used during germination and early seedling growth in either species.

Seed Biology of the Invasive Species Buffalobur (Solanum rostratum) in Northwest China

Buffalobur is an invasive summer annual species in Xinjiang Province, China. Our purpose was to investigate certain aspects of the seed biology of this weedy species that might be useful in controlling it. In contrast to a previous report that fresh seeds have physical (water-impermeable seed coat) plus physiological (low growth potential of embryo) dormancy, our results, along with those of others, verify that the seeds have only physiological dormancy. The seed's coat is water-permeable, the embryo is fully developed at seed maturity, and dormancy can be broken by cold stratification in the field during winter and early spring. Fifty-five percent of seeds buried in the soil in autumn germinated in the soil the following May, and 53% of the remaining nongerminated seeds germinated when tested in light in the laboratory. Thus, about 20% of the seeds did not germinate but were viable, demonstrating that the species forms at least a short-lived persistent seed bank. This information will be useful in planning a management strategy for this highly invasive species in northwest China.

Two-hundred-year seed survival of Leucospermum and two other woody species from the Cape Floristic region, South Africa

The ability of orthodox seeds to survive long-term dry storage is a key prerequisite for ex situ seed conservation in genebanks. However, only a few credible observations of seed survival for ≥ 200 years have been reported. In this paper, seed survival is shown for three species under suboptimal storage conditions for a documented time of ≥ 203 years and carbon dated at 218–270 years. Two species that germinated are in the Fabaceae (Liparia sp. and Acacia sp.). A water-impermeable seed coat, and hence an inability to equilibrate with ambient relative humidity, may contribute to long-term survival of these species. The third species that germinated (Leucospermum sp.) does not have a water-impermeable seed coat, and long-term survival may be linked to an oxygen-impermeable barrier in the seed. These results for species from the Cape Floristic Region, South Africa, suggest adaptation for extreme longevity in seeds of species of seasonally dry, Mediterranean environments.

Combinational dormancy in seeds of the Western Australian endemic species Diplopeltis huegelii (Sapindaceae)

Seeds of the endemic Western Australian species Diplopeltis huegelii Endl. were successfully germinated after the presence of combinational dormancy was identified, following the observation of selected seed characteristics. D. huegelii seeds were found to have large, fully developed, peripheral coiled embryos (with no endosperm) that are 7–8 mm long when uncoiled. Seed-coat dormancy was overcome by dipping seeds in hot water for ≥15 s, but seeds also required a period of after-ripening before they would germinate readily. After-ripening occurred while intact seeds were stored dry at ambient laboratory conditions for 13 months or when scarified (hot-water treated) seeds were stored at 13, 23 or 50% RH at 23°C for 6 weeks. Scarified 13-month-old seeds germinated readily at 7/18, 13/26 and 18/33°C in a 12-h photoperiod and in constant darkness, whereas scarified 1-month-old seeds germinated to ≤43%. Thus, seed dormancy in this species is caused by a water-impermeable seed coat (physical dormancy, PY) and a (non-deep) physiologically dormant embryo (PD), i.e. combinational dormancy (PY + PD). This is only the second report of combinational dormancy in seeds of Sapindaceae and the first report in this family of the PD component of (PY + PD) being broken during dry storage.