Seed germination in Marathrum schiedeanum and M. rubrum (Podostemaceae)

Marathrum schiedeanum and Marathrum rubrum are annual Podostemaceae, thus their seeds are important to their dispersal and persistence in their habitat. We assessed the effect on germination of (1) light (white, red and far red) and darkness, (2) temperature (15, 20, 25, 30 °C and alternating 20/30 °C), (3) osmotic potential (0 to −0.8 MPa), (4) proximity to moisture sources and (5) seed storage. Seeds of M. schiedeanum and M. rubrum were non-dormant and had a high germination capacity (96%). Seeds were positive photoblastic; at 15 °C germination drop to zero, and germination rate was slower at 20 °C and at 20/30 °C than at 25 °C. A small proportion of seeds of both species germinated even at osmotic potentials as low as −0.6 MPa (11%) for M. rubrum and −0.8 MPa (70%) for M. schiedeanum. Seeds germinated only when near to the source of moisture (91.3–87.1% and 53.3–35.6% for M. schiedeanum and M. rubrum, respectively) and 2 years in dry storage did not modify their capacity to germinate. At the beginning of the rainy season, light and temperature in the rivers may be high enough for germination. The ability to germinate at low osmotic potential may be related to early germination during the rainy season. This may be because the seed mucilage assists in diffusion of water from the substrate to the seed. Both species germinated faster at −0.06 MPa, than in distilled water, which may indicate appropriate conditions for germination of these short-lived species.     

Ovule morphology, embryogenesis and seed development in three Hylocereus species (Cactaceae)

Pre-embryonic and embryonic stages and seed developments were studied in the diploids Hylocereus monacanthus and Hylocereus undatus and the tetraploid Hylocereus megalanthus. Ovule morphology was similar among species except for micropyle entrance. H. monacanthus had the thickest and most robust suspensor. Embryo developmental time, measured from fertilization to maturity, was significantly more prolonged in H. megalanthus. Typical to Cactaceae, the seed coat was formed by one layer of sclerenchymatous cells, but was more lignified in H. megalanthus. Morphological features common to all species included (1) cellular type endosperm with independent patterns of development in the chalazal and micropylar zones, forming a haustorium layer from the chalazal zone to the embryo; (2) an endothelial layer surrounding the embryo sac almost complete; (3) a nucellar summit growing into the micropyle; and (4) a placental obturator and a funicle connecting the ovarian tissue to the ovule. Seed development was typically endospermic (exendospermic orthodox seeds). Anomalies included two egg cells in the same embryo sac, two embryos developing in the same ovule, and embryos developing from the chalazal pole region. Total seed number and seed viability were significantly lower in H. megalanthus than in the other two taxa. Embryos at different developmental stages were observed in aborted H. megalanthus seeds.     

Ecological and morphological seed traits of Polygala sardoa and P. sinisica: A comparative study on two endemic species of Sardinia

Polygala sardoa Chodat and P. sinisica Arrigoni (Polygalaceae) are two exclusive endemics to Sardinia and P. sinisica is affiliated under “Critically Endangered” in the IUCN Red Lists. In this work comparative studies on two populations of P. sardoa and in the only one of P. sinisica were carried out. In particular, seed output calculations and morphometric measurements on seed and elaiosome sizes were carried out. The effect of chipping, constant (15 °C) and alternating (25/10 °C) temperature regimes and light (8 h irradiance/day and dark) on germination were investigated. Seedling vigor assessments and a study on seed persistence in the soil were also carried out. P. sinisica had a higher seed output than P. sardoa and P. sinisica seeds were smaller than those of P. sardoa, with lower elaiosome area and elaiosome ratio values. Neither species had alternating temperature or light requirements for germination. P. sardoa achieved high germination percentages (> 80%) at all the tested conditions. P. sinisica had a lower maximum germination (<60%), suggesting the presence of physiological dormancy, and took more than twice as long to reach the maximum germination percentage. Seedlings of P. sardoa were larger than those of P. sinisica, and neither species formed a persistent soil seed bank. These new data may help implement effective conservation measures for these two species and, more generally, for threatened endemic species of this genus.     

Aerial seed bank and dispersal traits in Anthemis chrysantha (Asteraceae), a critically endangered species

Mature plant density and fruit production were monitored in the main population of four successive cohorts of the endangered winter annual Anthemis chrysantha (Asteraceae) in southeastern Spain. Experiments were conducted with artificial rainfall and a wind tunnel to determine the temporal and spatial dispersal pattern of the species and the relationship with rain and wind.     

Seed germination in temperate rain forest species of southern Chile: chilling and gap-dependency germination

Canopy gap and chilling requirements for seed germination were assessed in 61 and 44 species, respectively, in the temperate rain forest of southern Chile. Germination assays within canopy gap and understorey were carried out under natural conditions. Germination tests in cold stratified and non-stratified seeds were performed under laboratory conditions. Seeds were collected of common trees, shrubs, vines and perennial herbs of forests in southern Chile. Final percent germination was significantly enhanced under canopy gap conditions in 19 species, and significantly reduced in 11 species. Germination proved indifferent under gap vs. understorey conditions in half the species tested. Cold stratification affected germination in 11 species: significantly increasing final germination of four species, and significantly decreasing final percent germination of seven species. A Principal Components Analysis (PCA) was applied with the purpose of identifying groups of species with similar germination strategies. Four attributes were included in the PCA: final germination percentage in canopy gap, germination rate in the laboratory, and gap-and chilling-dependency indices (EGAP and STRAT, respectively). The first axis separated species mainly on EGAP variation while the second axis separated them mainly according to STRAT variation; the two axes together explaining 73% of the among-species variation. A small group of trees and vines germinating best in the understorey and neutral to chilling could clearly be distinguished from the remaining species analyzed. Multifactorial ANOVAs were used for evaluating the combined effect of successional status, seed mass, dispersal period, life form, phylogenetic categories, and dispersal syndrome on EGAP and STRAT variation. The EGAP value of secondary successional species proved significantly greater than that of primary successional species and species with endozoochorous seed dispersal were significantly less dependent on chilling (according to STRAT values) compared to species with mainly wind-dispersed seeds. The possible implications of these results for seedling establishment are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Serotiny and seed germination in three threatened species of Mammillaria (Cactaceae)

Individuals of some species of Mammillaria (Cactaceae) store some seeds on the plant over periods exceeding 1 year (serotiny). We examined the phenomenon of serotiny and germination behaviour of three rare and endangered Mammillaria species that occur in central Mexico. The species with the highest seed retention was Mammillaria solisioides, whose individuals kept on average 24% of their total seed crop throughout their observable lifetime. Individuals of Mammillaria napina and Mammillaria hernandezii did not differ in their degree of seed retention (about 5%). In M. solisioides and M. hernandezii, seed germination declined significantly with seed age, whereas in M. napina germination increased slightly. In all three species, over 70% of retained seeds were still alive after 8 years. Increasing fractions of dormant seeds were observed with seed age in M. solisioides and M. hernandezii, whereas in M. napina this fraction followed the opposite trend. All three species showed strict light dependence for germination. Serotiny was positively correlated with the harshness of the environment when species and populations were assumed independent. However, these correlations were not significant at the 5% level when the degree of relatedness of species and populations was taken into account using phylogenetically independent constrasts. We hypothesise that serotiny in these species represents a mechanism by which they can cope with a harsh, unpredictable environment. To our knowledge, this is the first assessment of serotiny in cacti.     

Zygospore overwintering and sporulative germination in Triplosporium fresenii (Entomophthoraceae) attacking Aphis spiraecola on citrus in Israel

Triplosporium (Entomophthora) fresenii overwinters on citrus trees in Israel as zygospores which germinate in March and April by means of capillary conidiophores bearing capillispores (anadhesive conidia) in synchronization with spring buildup of Aphis spiraecola populations on citrus. The minimum temperature for zygospore germination in Israel is about 9–10°C. In the zygospore population there is variability regarding time needed to break dormancy and temperature needed for germination, which is gradual, its cumulative curve being sigmoidally shaped. Some evidence suggests that dormancy is of the endogenous type. The variability and the ability to overwinter on trees as resting spores are assumed to give T. fresenii an advantage over other Entomophthoraceae present on the same host in spring.     

Allelopathic potential of Bothriochloa laguroides var. laguroides (DC.) Herter (Poaceae: Andropogoneae)

Bothriochloa laguroides var. laguroides (DC.) Herter, a native bluestem of America, has been shown to produce many biologically active compounds. The allelopathic potential of aqueous extracts from roots, stems and leaves was examined. Lettuce seeds (Lactuca sativa) and maize (Zea mays), the common allelopathy bioassay systems, as well as seeds from two native species, wintergreen paspalum (Paspalum guenoarum) and lovegrass (Eragrostis curvula), were germinated in the presence of aqueous extracts. Percent seed germination, root and shoot elongation were measured. After 4 and 7 days root, stem and leaf extracts caused inhibition of root and shoot elongation in all four species tested. Aqueous extracts were generally less inhibitory to seed germination. Aqueous extracts from different parts of B. laguroides var. laguroides show therefore allelopathic effects inhibiting, in particular, growth of competing plants.     

The pathways of amino acid oxidation during germination of mustard seeds (Sinapis alba)

During the germination of Sinapis alba seed, alanine and some other amino acids were oxidized via the tricarboxylic acid cycle (TCA), although the pentose phosphate pathway (PPP) was also operative and may account for ca 50% of glucose oxidation. The relative operation of the PPP and the TCA cycle was influenced by changes in the concentrations of glutamic acid and glycine.     

The levels of two distinct species of phytochrome are regulated differently during germination in Avena sativa L.

The abundance and molecular mass of phytochrome in germinating embryos of A. sativa (oat) grown in light or darkness have been monitored using immunoblot and spectrophotometric assays. Immunoblot analysis shows that imbibed but quiescent embryos have two immunochemically distinct species of phytochrome with monomeric molecular masses of 124 and 118 kDa (kdalton). The 118-kDa species has the properties of the 118-kDa phytochrome extracted from fully green oat tissue (J.G. Tokuhisa, S.M. Daniels, P.H. Quail, 1985, Planta 164, 321–332), whereas the 124-kDa polypeptide appears similar to the well-characterized photoreceptor of etiolated tissue. The capacity of antibodies directed against etiolated-oat phytochrome to immunoprecipitate the 124-kDa species but not the 118-kDa species has been exploited to quantitate the levels of each separately over a 72-h time course of germination and seedling development. The abundance of the 124-kDa molecule increases at least 200-fold in etiolated seedlings over 72 h whereas in light-grown seedlings the level of this molecule is relatively constant. In contrast, the amount of the 118-kDa species increases only twofold in both dark- and light-grown seedlings over the same period of time. These data indicate that whereas the abundance of 124-kDa phytochrome is regulated at the protein level by the well-documented, differential stability of the red- and far-red-absorbing forms in vivo, the 118-kDa molecule is present at a low constitutive level, presumably reflecting no such difference in the stability of the two spectral forms.Abbreviations ELISA enzyme-linked immunosorbent assay - Ig immunoglobulin - kDa kilodalton - Pfr, Pr far-red-absorbing and red-absorbing forms of phytochrome, respectively - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Seedling morphology of three sympatric savanna species of Byrsonima: First evidence of cryptogeal germination in Malpighiaceae and an overlooked seedling type in eudicots

Byrsonima crassifolia (L.) Kunth, B. coccolobifolia Kunth and B. verbascifolia (L.) DC. (Malpighicaceae) are sympatric species with high ecological importance in the Roraima savannas of northern Brazil. The three species can be distinguished by seedling characters. The phanerocotylar, epigeal, foliaceous seedling of B. crassifolia is similar to other forest species in the genus. On the other hand, both B. coccolobifolia and B. verbascifolia have phanerocotylar, hypogeal, foliaceous seedlings, representing a newly defined seedling group among eudicot seedling types. Byrsonima verbascifolia has a reduced epicotyl and short subsequent internodes, whereas the long cotyledonary petioles are diagnostic for B. coccolobifolia. Both B. coccolobifolia and B. verbascifolia have cryptogeal germination, which involves characters that presumably protect the plumule from the recurrent fires they are subjected in savannas (e.g., plumule burying, cotyledonary node below the soil surface, and fusion of cotyledonary petioles). This is the first report of cryptogeal germination in the Malpighiaceae as well as in Neotropical eudicots.     

The role of GA3 in the germination process of high-mountain endemic and threatened species: Leontopodium nivalePinguicula fiorii and Soldanella minima subsp. samnitica (central Apennines,Italy)

The ex situ conservation of biodiversity is an essential tool for environmental protection interventions. Germination studies of seeds that belong to endangered species are essential for ex situ conservation strategies. In this study, we investigate the germination responses of three high-altitude endemic and vulnerable species (Leontopodium nivale, Pinguicula fiorii and Soldanella minima subsp. samnitica). Specifically we identified potential dormancy mechanisms by investigating the responses of germination percentage and rate to different concentrations of gibberellic acid (GA₃), by performing a general linear model. L. nivale reached a germination percentage of 98.0 ± 2.0% (mean ± SE) under control conditions (20°C; 12/12 photoperiod; no GA₃ addition). P. fiorii showed the highest germination percentage (78.0 ± 2.0%) in the treatment with GA₃ 500 ppm. S. minima subsp. samnitica did not show sensitivity to GA₃ but responded positively to cold stratification (6 month at 5°C) with a germination percentage of 90 ± 6%. This study made it possible to acquire important information on the germination process of threatened and rare endemic taxa.     

Teaching techniques for mycology: 24. Patterns of basidiospore germination in Auricularia (Heterobasidiomycetes)

‘Basidiocarps of Auricularia can be stored dry, discharging ballistospores upon rehydration. This article describes methods to demonstrate basidiospore germination by repetition or formation of a primary mycelium and/or microconidia’     

Interactive effects of salt and alkali stresses on seed germination,germination recovery,and seedling growth of a halophyte Spartina alterniflora (Poaceae)

Soil salinization and alkalinization frequently co-occur in nature, but there is little information on the interactive effects of salt and alkali stresses on plants. Seed germination and early seedling growth are crucial stages for plant establishment. We investigated the interactive effects of salt and alkali stresses on seed germination, germination recovery and seedling growth of a halophyte Spartina alterniflora. Seed germination percentage was not significantly reduced at low salinity (≤ 200 mM) at pH 6.63–9.95, but decreased with increased salinity and pH. Ungerminated seeds germinated well after transfer to distilled water from treatment solutions, indicating that seeds can remain viable in high salt–alkaline habits. Shoot growth was stimulated at low salinity and pH, but decreased with increased salinity and pH. Radicle elongation decreased sharply with increased salinity and pH, and was significantly inhibited when pH ≥ 9.0, indicating that the radicles are very sensitive to salt–alkaline stress. The deleterious effects of salinity or high pH alone were less than when combined. A reciprocal enhancement of salt and alkali stresses is a characteristic feature for salt–alkaline stress. Stepwise regression analysis indicates that salinity is the dominant factor, while pH and buffer capacity are secondary for salt–alkaline mixed stress.     

Seed germination and seedling performance of two Mediterranean tree species,holm oak (shape Quercus ilex L.) and Aleppo pine (shape Pinus halepensis Mill.): a multifactor experimental approach

A two-level multifactor experimental approach was used to compare seed germination and seedling performance of two Mediterranean tree species: the early successional Aleppo pine (Pinus halepensis Mill.) and the late successional holm oak (Quercus ilex L.). In a first experiment germination rate was evaluated under the combined effects of shade, nitrogen availability, and pine or holm oak leaf litter. In a second experiment we tested for the effects of shade, nutrient availability, and litter type on seedling survival, growth and biomass allocation. Holm oak showed higher germination rates under shaded than under unshaded conditions, while Aleppo pine showed no differences between shaded and unshaded conditions. Nitrogen availability and litter type had no significant effect on germination of either species. Both species showed increased RGR, but also higher mortality rates, when grown in an enriched nutrient environment. While Aleppo pine showed no differences in RGR and mortality rate under different shading levels, RGR decreased and mortality increased for holm oak in full light. Increased radiation decreased LAR, SLA and height:diameter ratio, and increased RWR and R/S in both species, although Aleppo pine showed more pronounced changes. Unlike Aleppo pine, holm oak responded to increased nutrient availability by decreasing R/S and increasing LAR. From these results, no seed-seedling conflicts were found in either species, but a trade-off does seem to exist for holm oak between biomass allocation traits deployed in response to increased nutrient availability and radiation. Aleppo pine outperformed holm oak under most environmental conditions tested and showed a wider regeneration niche.     

Some morphological and anatomical observations during alleviation of salinity (NaCI) stress on seed germination and seedling growth of barley by polyamines

In this work, the effects of polyamine (cadaverine, putrescine, spermidine, spermine) pretreatments on the germination of barley seeds, seedling growth under saline (NaCI) conditions and on leaf anatomy of the seedlings grown for 20 days in pots with perlite containing different concentrations of NaCI prepared with Hoagland solutions following the germination period of 7 days were studied. The inhibitive effect of salt on seed germination and seedling growth was alleviated in varying degrees, and dramatically, by polyamine pretreatments at the levels of NaCI studied; particularly with lower levels of salt, the control seeds were able to germinate with great difficulty. Also, the successes of these pretreatments continued, even decreased, with higher levels of NaCI such that the control seeds showed no germination. On the other hand, on the various parameters of leaf anatomy of barley seedlings, interactions between pretreatments of polyamine and salinity, with some of these being statistically important, were observed.     

Seed dispersal and germination patternsin a rare Mediterranean island endemic (Anchusa crispa Viv., Boraginaceae)

We analyse and discuss patterns of seed dispersal and germination of a rare endemic plant species, Anchusa crispa Viv. (Boraginaceae) from Corsica and Sardinia. This coastal plant inhabits dunes and back-dunes, and currently numbers only a few thousand individuals which generally occur in isolated populations. This study included experiments conducted in the field in Corsica and also under controlled conditions in the laboratory. Short-distance dispersal of A. crispa is performed by ants, both by myrmecochory and dyszoochory. The invasion of an exotic species of ant, Linepithema humile, could locally modify the dispersal system and possibly the population dynamics of A. crispa. Long-distance dispersal may occur by water transport since seeds can germinate after at least 1 week of immersion in seawater and readily float on the surface. Burial of seeds is favourable for germination, percentage germination being maximised at a depth of 1–2 cm below the soil surface. A. crispa has a seed bank of about ten viable seeds per m², which may contribute to the survival of this species which exists in small populations with a short life span. Due to its seed dispersal and germination patterns, the conservation of this species will necessitate that human disturbance, which can destabilise the surface of the sand is prevented and that new populations are introduced to favourable sites.