Light Requirement For Germination Research Articles

Inter-provenance variation in seed germination response of a cash crop halophyte Suaeda fruticosa to different abiotic factors

Information about provenance-based differences in seed attributes of potential cash crop halophytes is limited but important to define sources for the highest quality seeds. This study examined inter- provenance variations in seed morphology, germination, and tolerance responses of Suaeda fruticosa to common abiotic factors. Seed size varied significantly among provenances, and the largest sized seeds were developed in the highly moist moderately-saline coastal area of Manora. Seed germination responses also varied among provenances and seeds from highly moist provenance of Manora showed the highest germination in 400 mM NaCl in light under low to moderate temperature regimes. The light requirement for germination was lowest in the seeds from highly saline provenance of Gaddani. The highest germination recovery of un-germinated seeds from the high salinity (600 mM NaCl) was for seeds from dry provenance of Bahawalpur irrespective of temperature regime. Recovery for seeds from the (moderately) moist (highly) saline provenances of Gaddani and Hawke's Bay was highly temperature-dependent. However, recovery of dark-incubated un-germinated seeds after transfer to light was salinity-dependent, but not dependent on provenance. Thus, these data indicate that provenance can affect the size, germinability, and stress tolerance of S. fruticosa seeds. Generally, seeds from less stressful provenance of Manora had better quality, i.e., larger size, higher germination, and qualify for mass-scale cultivation / restoration programs under most environmental conditions.

Seed germination characteristics of an endangered evergreen broadleaf tree, Rhododendron uwaense

ABSTRACT The importance of plantation forests in the conservation of endangered species has increased over time. Rhododendron uwaense is a small, endangered, evergreen broadleaf tree first described in 1984. This species only occurs in plantations and secondary forests on a small watershed in Shikoku, western Japan. Between the first observation of the species and 2017 no forest management practices had been conducted within the species’ range; however, the landowner began thinning operations in 2017. If this species has light requirements for germination as like some Rhododendron species, forest management practices that improve light availability may facilitate the establishment of the species. To reveal the germination characteristics and the appropriate storage conditions and length for R. uwaense seeds, we assessed differences in the germination of seeds stored under different conditions (indoor, outdoor, moist chilled and dry chilled) and for varying durations (45, 90, 136, 180, 225 days) by the gradually increasing and decreasing temperature method. Germination was higher in the increasing temperature regime. This trend is common among plant species with physiological dormancy that is broken by chilling, allowing seeds to germinate in the spring. Seeds that were collected during the dispersal period germinated immediately after collection, but germination required the presence of light. Seeds stored indoors for more than 180 days failed to germinate. Seeds stored dry chilled for 225 days still maintained a germination rate of more than 60%. Improvement of forest floor light conditions and seed storage under dry chilled conditions are recommended for seed germination and propagation.

Variable seed bed microsite conditions and light influence germination in Australian winter annuals

Environmentally cued germination may play an important role in promoting coexistence in Mediterranean annual plant systems if it causes niche differentiation across heterogeneous microsite conditions. In this study, we tested how microsite conditions experienced by seeds in the field and light conditions in the laboratory influenced germination in 12 common annual plant species occurring in the understorey of the York gum-jam woodlands in southwest Western Australia. Specifically, we hypothesized that if germination promotes spatial niche differentiation, then we should observe species-specific germination responses to light. In addition, we hypothesized that species’ laboratory germination response may depend on the microsite conditions experienced by seeds while buried. We tested the laboratory germination response of seeds under diurnally fluctuating light and complete darkness, which were collected from microsites spanning local-scale environmental gradients known to influence community structure in this system. We found that seeds of 6 out of the 12 focal species exhibited significant positive germination responses to light, but that the magnitude of these responses varied greatly with the relative light requirement for germination ranging from 0.51 to 0.86 for these species. In addition, germination increased significantly across a gradient of canopy cover for two species, but we found little evidence to suggest that species’ relative light requirement for germination varied depending on seed bank microsite conditions. Our results suggest that variability in light availability may promote coexistence in this system and that the microsite conditions seeds experience in the intra-growing season period can further nuance species germination behaviour.

Response of central Amazon rainforest soil seed banks to climate change - Simulation of global warming

The most severe global warming is predicted to occur in the Amazon region of Brazil, with an estimated temperature increase of 4 to 8 °C between 2071 and 2100. Our study evaluated the effects of increased temperatures on germination success of seeds in the soil seed bank of secondary forests in Central Amazonia. Soil samples (3-cm depth) were collected in six secondary forests with different land-use histories and ages of regrowth. Soils from all sites were sieved and mixed, and germination and seedling development were assessed during 4 months of incubation in germination chambers at (1) a constant temperature of 25 °C and a 12:12 h alternating temperature regime of 20:30 °C, considered as controls; (2) a simulated 5 °C temperature increase to 30 °C and 25:35 °C and (3) a 10 °C temperature increase to 35 °C and 30:40 °C. To determine the effect of light vs. dark on germination, germination was compared for samples in light (12 h daily photoperiod) vs. continuously dark for 1 month, followed by 3 months in light. Six temperature conditions were tested with 30 subsamples each. In the mixed soil seed bank, 3640 seeds germinated, of which 18 families, 28 genera and 41 species (grouped in 20 trees, 11 shrubs, eight herbs and two lianas) could be identified. A light requirement for germination was detected for 94–97% of the species. Alternating temperatures did not stimulate germination in the dark. Seedling density m−2 was 1.7 to 2.3 times higher at alternating (20:30 °C and 25:35 °C) than at constant temperatures (25 °C and 30 °C); but an increase of 10 °C decreased seedling density to 47% at 35 °C and 26% at 30:40 °C compared to control (100% at 25 °C and 20:30 °C); and furthermore increased seedling mortality. Thus, the secondary forest at the study area may maintain its integrity with a 5 °C but not with a 10 °C temperature increase. Species-specific sensitivities to temperature were detected. Temperature may function to fine-tune germination at a specific microsite, and the variety of germination requirements may enhance coexistence and maintenance of species diversity within the pioneer species subset. In general, seeds of tree species were more sensitive to increased temperatures than those of shrubs and herbs, supporting the hypothesis of replacement of the tropical forest by savanna-like vegetation in the Amazon region. Our results show that natural regeneration may be significantly affected by global warming and with potential to alter floristic composition.

Seed Dormancy and Soil Seed Bank of the Two Alpine Primula Species in the Hengduan Mountains of Southwest China.

The timing of germination has long been recognized as a key seedling survival strategy for plants in highly variable alpine environments. Seed dormancy and germination mechanisms are important factors that determining the timing of germination. To gain an understanding of how these mechanisms help to synchronize the germination event to the beginning of the growing season in two of the most popular Primula species (P. secundiflora and P. sikkimensis) in the Hengduan Mountains, Southwest China, we explored their seed dormancy and germination characteristics in the laboratory and their soil seed bank type in the field. Germination was first tested using fresh seeds at two alternating temperatures (15/5 and 25/15°C) and five constant temperatures (5, 10, 15, 20, and 25°C) in light and dark, and again after dry after-ripening at room temperature for 6 months. Germination tests were also conducted at a range of temperatures (5–30, 25/15, and 15/5°C) in light and dark for seeds dry cold stored at 4°C for 4 years, after which they were incubated under the above-mentioned incubation conditions after different periods (4 and 8 weeks) of cold stratification. Base temperatures (T b) and thermal times for 50% germination (θ 50) were calculated. Seeds were buried at the collection site to test persistence in the soil for 5 years. Dry storage improved germination significantly, as compared with fresh seeds, suggesting after-ripening released physiological dormancy (PD); however, it was not sufficient to break dormancy. Cold stratification released PD completely after dry storage, increasing final germination, and widening the temperature range from medium to both high and low; moreover, the T b and θ 50 for germination decreased. Fresh seeds had a light requirement for germination, facilitating formation of a persistent soil seed bank. Although the requirement reduced during treatments for dormancy release or at lower alternating temperatures (15/5°C), a high proportion of viable seeds did not germinate even after 5 years of burial, showing that the seeds of these two species could cycle back to dormancy if the conditions were unfavorable during spring. In this study, fresh seeds of the two Primula species exhibited type 3 non-deep physiological dormancy and required light for germination. After dormancy release, they had a low thermal requirement for germination control, as well as rapid seed germination in spring and at/near the soil surface from the soil seed bank. Such dormancy and germination mechanisms reflect a germination strategy of these two Primula species, adapted to the same alpine environments.

Effects of Light and Temperature on Germination of Eggert's Sunflower (Helianthus eggertii)

Helianthus eggertii is a rare perennial sunflower of barrens and open habitats in Kentucky, Tennessee, Alabama, and South Carolina in the United States (U.S.). Despite its delisting in the U.S. Endangered Species Act in 2005, little is known about the germination biology of H. eggertii other than seeds require cold stratification for optimal germination. Knowledge about the germination biology of rare species can aid in the management of natural populations and inform strategies for ex situ seed conservation and propagation. We examined how cold stratification, light, and temperature interact to affect seed germination in H. eggertii, and whether germination proportions varied among populations. At the time of maturity in October, seeds have primary physiological dormancy and require cold stratification or prolonged (> 8 wk) incubation in light at cool (15/6 C) temperatures to germinate. Seeds maintained a light requirement for germination when cold stratified in darkness, but not after cold stratification in light. However, seeds germinated to lower proportions after cold stratification in light relative to darkness, and when incubated at temperatures that mimic summer (35/20 C) compared to late spring (25/15 C). Germination varied widely among populations (23-58%), with plants from more open sites exhibiting lower germination proportions than those from partially shaded sites. Our results indicate seeds most likely germinate in early- to mid-spring, and light promotes germination of H. eggertii. Our results highlight the interactive role of light and temperature in determining seed dormancy break and germination in H. eggertii.

Light Requirements for Germination and Early Development of Cork Oak under Natural, Semi-Natural and Artificial Conditions

Light Requirements for Germination and Early Development of Cork Oak under Natural, Semi-Natural and Artificial Conditions

Germination ecology of the perennial herb Xyris longiscapa: inter-annual variation in seed germination and seasonal dormancy cycles

AbstractGermination ecology was investigated in a natural population of Xyris longiscapa, a perennial herbaceous species endemic to the Brazilian campo rupestre. Seeds were collected over four consecutive years (2014 to 2017) to evaluate germination responses to a range of temperatures (from 15 to 30°C). The light requirement was evaluated in seeds collected in 2014. Seeds collected in 2014 were also buried in soil in the natural habitat of the species to evaluate changes in germinability at different temperatures over the time. Seeds showed an absolute light requirement for germination. Seed germination was affected by temperature, collection year and the interaction between these two factors. Seeds collected in 2014 showed a narrower temperature range for germination (15–20°C), compared with the seeds collected in 2015, 2016 and 2017 that germinated in a temperature range of 15–25°C. Buried seeds remained viable in soil for at least 14 months and exhibited seasonal dormancy cycling. Secondary dormancy was induced during the rainy season and alleviated during the dry season, following a conditional dormancy/dormancy cycle. The degree of primary dormancy appeared to be influenced by the environmental conditions experienced by seeds during maturation. Primary dormancy (when present), seed persistence in soil and seasonal dormancy cycles are strategies of X. longiscapa to enhance regeneration success in the harsh environment of the Brazilian campo rupestre.

Seed germination of coastal monsoon vine forest species in the Northern Territory, Australia, and contrasts with evergreen rainforest

Seed germination traits of seasonal rainforest species differ from permanently moist evergreen rainforest species due to the prolonged seasonal drought. We investigated whether seed germination traits used to categorise evergreen rainforest species into pioneer and climax guilds were applicable to seasonal rainforest species. Seed dormancy, light requirements for germination and seed storage types of five climax and thirteen pioneer species of a coastal vine thicket were studied. Results were compared with published studies of evergreen rainforest species. Evergreen rainforest pioneer species are typically dormant, require light to germinate and tolerate desiccation, whereas climax species are typically non-dormant, tolerate shade during germination and are sensitive to desiccation. In seasonal rainforest we found that a high proportion of pioneer species had seeds that were non-dormant (62%), and a high proportion of pioneer species germinated equally well in light and dark conditions. In seasonal rainforest, we found that the majority of climax species had desiccation tolerant seeds, whereas in evergreen rainforest the proportion of climax species producing desiccation sensitive seeds is equal to or greater than the proportion of species with desiccation tolerant seeds. In seasonal rainforest species physical, physiological and epicotyl dormancy types were found. Generally, for seasonal rainforest species, the prevalent form of dormancy in pioneer species was physical dormancy whereas physiological dormancy was most common in evergreen rainforest pioneer species with dormancy. Our results suggest that the contrasting seed biology traits that typically apply to pioneer and climax species of evergreen rainforest species don’t typically apply to seasonal rainforest species.

Variation in the effects of burial in different peatland successional stages on seed survival of four wetland species

The availability of viable seeds in soil helps to determine the success of ecological restoration in disturbed habitats. Although seed survival in soil generally increases with an increase in burial depth, whether the effects of burial on seed survival are comparable across different sites is unclear. In this study, I tested the hypothesis that the positive effects of burial on seed survival decrease as vegetation develops through succession. Four wetland species, Drosera rotundifolia, Lobelia sessilifolia, Rhynchospora alba and Moliniopsis japonica, were used for the study. The four species differ in their light requirement for germination; i.e., D. rotundifolia, L. sessilifolia and R. alba germinate best in light, whereas M. japonica germinates equally well in light and darkness. The seeds of these species were buried for two years at three depths (litter, 0 and 4 cm) in three successional stages with different amounts of vegetation and litter in a post-mined peatland. The photosynthetically active radiation (PAR) and temperature at each of litter layer, 0 cm and 4 cm depths were measured for each successional stage. The between-depth differences in PAR and temperature fluctuations decreased as succession progressed. For the three light-demanding species, burial promoted seed survival more in the initial successional stage than in the later successional stages, whereas for M. japonica, burial promoted seed survival equally in all successional stages. This study revealed significant variation in the effects of burial on seed survival, particularly for light-sensitive seeds, and that the soil surface layers in vegetated sites can contain persistent seeds, which could be used as a seed source in restoration.

Temperature and Light Requirements for Germination and Emergence of Three Arable Papaveraceae Species

This research investigated the temperature and light requirements for seed germination and emergence patterns of pinnate poppy, violet horned-poppy, and nodding hypecoum, three annual Papaveraceae species found in arable lands in the Mediterranean region. Two experiments performed in growth chambers (1) analyzed light (complete darkness or 12 h light) and temperature (10/5, 15/5, and 20/10 C day/night temperatures) requirements for germination, and (2) determined base temperature (Tb) for germination. An outdoor pot trial was also set up to study emergence patterns. All species showed higher germination in complete darkness than they did with a light regime, irrespective of dormancy level, time of the year, and temperature regime under which germination was tested, illustrating better germination when seeds are buried.Tbranged from −2.6 to 0 C, depending on the species, indicating low temperature requirements for germination. Given their higher germination in daily fluctuating, rather than constant temperatures, the three Papaveraceae species should have the capacity to form persistent seed banks. These species behaved as winter annuals (from November to February) in the pot experiment and had difficulties to emerge in spring. Given that they cannot avoid autumn–winter chemical treatments, this could partially explain their regression in arable fields. These results bring new information to develop management strategies for these Papaveraceae species in agroecosystems.

Seed mass, germination and seedling traits for some central Argentinian cacti

AbstractSeed size is one of the most important traits in the regenerative phase of a plant's life cycle; however, for cactus species the relationship of seed size and germination characteristics and seedling traits is still unclear. We studied the relationship between seed mass and germination and seedling characteristics in 17 cactus species from central Argentina, belonging to different genera and life forms. We measured seed mass, total seed germination, light requirements for germination and mean time to germination for these 17 cacti species; in addition, we recorded seedling size and shape in 15 species. To test light requirements we performed germination experiments under laboratory conditions at 25/15°C (day/night temperatures) and under light or dark conditions. We also calculated seedling volume by measuring seedling height and width. A shape index was obtained by dividing height by width (a value of 1 indicates ‘globose’ seedlings, whereas, as this value increases, seedlings become ‘columnar’). We found no significant relationship between seed mass and any of the germination characteristics considered. However, species with heavier seeds produced bigger seedlings, which were more cylindrical. Adult growth was not totally determined by seedling ‘growth form’, because some species that had globose seedlings were columnar at the adult stage.

Campanulaceae: a family with small seeds that require light for germination

The Campanulaceae is a large cosmopolitan family, but is understudied in terms of germination, and seed biology in general. Small seed mass (usually in the range 10-200 µg) is a noteworthy trait of the family, and having small seeds is commonly associated with a light requirement. Thus, the purpose of this study was to investigate the effect of light on germination in 131 taxa of the Campanulaceae family, from all five continents of its distribution. For all taxa, seed germination was tested in light (8 or 12 h photoperiod) and continuous darkness under constant and alternating temperatures. For four taxa, the effect of light on germination was examined over a wide range of temperatures on a thermogradient plate, and the possible substitution of the light requirement by gibberellic acid and nitrate was examined in ten taxa. For all 131 taxa, seed germination was higher in light than in darkness for every temperature tested. Across species, the light requirement decreased significantly with increasing seed mass. For larger seeded species, germination in the dark reached higher levels under alternating than under constant temperatures. Gibberellic acid promoted germination in darkness whereas nitrates partially substituted for a light requirement only in species showing some dark germination. A light requirement for germination, observed in virtually all taxa examined, constitutes a collective characteristic of the family. It is postulated that smaller seeded taxa might germinate only on the soil surface or at shallow depths, while larger seeded species might additionally germinate when buried in the soil if cued to do so by fluctuating temperatures.

SEED GERMINATION BEHAVIOUR OF THREE ALPINE SPECIES FROM ULUDAĞ MOUNT,TURKEY

In this study, the germination requirements of three species from alpine belt of Uludag Mount; Gypsophila olympica Boiss., Matthiola montana Boiss. and Silene rhynchocarpa Boiss. We tested the germination under (20 °C) dark, (20 °C) continuous light, and photoperiod 20/10 °C (12/12h) with distilled water. Different germination behaviour was found for these three species from closely related habitat conditions. G. olympica showed similar germination percentages in dark, light and photoperiod, and germinated faster in light (3.9 days). S. rhyncocarpa germinated 100 % at all the three conditions but faster in dark with 2.0 days. M. montana seeds were found to require light for germination. The germination was 27.2 % at dark, whereas the seeds were germinated 90 % under photoperiod. The results can be useful for both in situ and ex situ conservation of these plant species. Normal 0 21 false false false TR X-NONE X-NONE

Germination patterns and ecological characteristics of Vellozia seeds from high-altitude sites in south-eastern Brazil

AbstractThe present work aims to determine whether there are patterns of seed and germination characteristics in Vellozia due to the phylogenetic proximity among the species examined and if these characteristics explain their restricted geographical distributions. We evaluated the germination characteristics of freshly collected seeds from 13 species of the genus Vellozia (Velloziaceae) that show different degrees of endemism, collected at various locations in the Espinhaço Mountain Range in Minas Gerais State, south-eastern Brazil. The size and mass of the seeds, as well as the influence of light and temperature on their germination, were measured. Experiments were performed in germination chambers under constant temperatures of 10–40°C (intervals of 5°C), with a 12-h photoperiod, as well as in continuous darkness. All species studied had small seeds with mass varying from 0.06 to 1.21 mg. Most species required light for germination, displaying high germinability in the range of 15–40°C; some species, however, germinated in the absence of light at the highest temperatures (35 and 40°C). The sizes and masses of the seeds showed significant linear correlations, but light sensitivity was not related to these seed characteristics. The responses observed suggest that light requirement for germination, associated with the small sizes of Vellozia spp. seeds, contribute to the formation of persistent seed banks. The observed tolerance of these seeds to a wide range of germination temperatures is consistent with the large daily temperature fluctuations experienced in campos rupestres sites, although these seed characteristics cannot by themselves explain the high degree of endemism or the restricted distributions observed among the species examined.

Regeneração de espécies arbóreas e relações com componente adulto em uma floresta estacional no vale do rio Uruguai, Brasil

O estudo de fenômenos relacionados às variações na estrutura das comunidades vegetais tem cada vez mais envolvido a avaliação do potencial de regeneração das espécies arbóreas, uma vez que a regeneração torna as florestas capazes de se restaurarem após distúrbios naturais ou antrópicos. Neste sentido, objetivou-se avaliar o componente arbóreo regenerante, identificando composição e abundância, grupos funcionais de dispersão, estratificação vertical e necessidades de luz para germinação, além de estimativas de riqueza e diversidade e comparar estes valores com o respectivo componente adulto. O levantamento foi realizado em 20 unidades amostrais de 10 x 10 m, sendo amostrados todos os indivíduos com altura > 0,30 m e diâmetro a altura do solo < 4,7 cm. O levantamento do componente adulto, avaliado em estudo anterior, foi estabelecido em unidades amostrais de 20 x 20 metros, sendo amostrados todos os indivíduos com diâmetro à altura do peito > 4,7 cm. Foram amostrados 1.649 indivíduos em regeneração, pertencentes a 64 espécies, com densidade total estimada em 8.245 ind.ha-1. As espécies com maior densidade absoluta foram Gymnanthes concolor Spreng., Trichilia elegans A.Juss. e Calyptranthes tricona D.Legrand. Uma análise de coordenadas principais indicou nítida separação das unidades amostrais amostradas e um teste de Mantel revelou haver independência entre as matrizes de composição e abundância dos componentes adulto e regenerante (r = 0,19; p = 0,1). Dentre os grupos funcionais, verificou-se que o componente regenerante está mantendo as mesmas proporções observadas para o componente adulto, com maior proporção de espécies zoocóricas, dependentes de luz para germinação e formadoras do dossel florestal. Ao contrário do esperado, houve diminuição da riqueza no componente regenerante (p < 0,001) e manutenção da equabilidade ao longo da área.

Germination traits explain soil seed persistence across species: the case of Mediterranean annual plants in cereal fields

Seed persistence in the soil under field conditions is an important issue for the maintenance of local plant populations and the restoration of plant communities, increasingly so in the light of rapidly changing land use and climate change. Whereas processes important for dispersal in space are well known, knowledge of processes governing dispersal in time is still limited. Data for morphological seed traits such as size have given contradictory results for prediction of soil seed persistence or cover only a few species. There have been few experimental studies on the role of germination traits in determining soil seed persistence, while none has studied their predictive value consistently across species. Delayed germination, as well as light requirements for germination, have been suggested to contribute to the formation of persistent seed banks. Moreover, diurnally fluctuating temperatures can influence the timing of germination and are therefore linked to seed bank persistence. The role of germination speed measured by T(50) (days to germination of 50 % of all germinated seeds), light requirement and reaction to diurnally fluctuating temperatures in determining seed persistence in the soil was evaluated using an experimental comparative data set of 25 annual cereal weed species. It is shown that light requirements and slow germination are important features to maintain seeds ungerminated just after entering the soil, and hence influence survival of seeds in the soil. However, the detection of low diurnally fluctuating temperatures enhances soil seed bank persistence by limiting germination. Our data further suggest that the effect of diurnally fluctuating temperatures, as measured on seeds after dispersal and dry storage, is increasingly important to prevent fatal germination after longer burial periods. These results underline the functional role of delayed germination and light for survival of seeds in the soil and hence their importance for shaping the first part of the seed decay curve. Our analyses highlight the detection of diurnally fluctuating temperatures as a third mechanism to achieve higher soil seed persistence after burial which interacts strongly with season. We therefore advocate focusing future research on mechanisms that favour soil seed persistence after longer burial times and moving from studies of morphological features to exploration of germination traits such as reaction to diurnally fluctuating temperatures.

Underdeveloped embryos and germination in Aristolochia galeata seeds

Aristolochiaceae have been described as having seeds with underdeveloped embryos and morphological or morphophysiological dormancy. Aristolochia galeata is a native climber found in the Cerrado biome, associated with road and gallery forest edges. The aims of this study were to investigate: embryo growth rate, morphology and seed germination parameters under different treatments. Embryos were excised to obtain embryo length at four stages: initial, seeds after coat rupture, radicle tip protrusion and cotyledon emergence from the seed coat. Germination tests were conducted at 30 °C under three nitrate concentrations (1, 10 and 20 mM), fluctuating temperature (27/20 °C) and light and dark conditions. We found that seeds have underdeveloped embryos, which take about 301 ± 178 h (±SD) to achieve seed coat rupture, another 205 ± 126 h to reach radicle protrusion and 176 ± 76 h more to the final stage of cotyledon emergence. Germinability was above 52% in all treatments, except in the dark (15%). For all treatments, average germination time was above 290 ± 123 h. Potassium nitrate increased germinability to >87%. No particular treatment was required for embryo development, but seeds in the population that continued to germinate after 1 month were probably in various states of non-deep, simple morphophysiological dormancy. Increased germinability in nitrate treatments and light requirement for germination could prevent germination under unsuitable environmental conditions and be a strategy to increase seedling establishment in the cerrado.

Germination characteristics of Syngonanthusseeds (Eriocaulaceae) incampos rupestresvegetation in south-eastern Brazil

AbstractThe present study evaluated the size and germination characteristics of seeds of seven species ofSyngonanthus(distributed among four sections) that occur in different microhabitats incampos rupestresvegetation in Minas Gerais State, to determine if (1) the germination responses of the various species characterize a single germination pattern for the genus; and (2) there is a correlation between the germination characteristics and the geographic distribution as well as the microhabitat of the different species. The experiments were undertaken with recently collected seeds exposed to a 12-h photoperiod and continuous darkness, at constant temperatures of 10–40°C (at intervals of 5°C) in germination chambers. The results indicated the existence of a pattern of reduced seed size and light requirements for germination within the genus. The geographic distribution of different species of the genus cannot be explained by the responses of seed germination to different temperatures, but suggests some relationship to their edaphic microhabitats. Therefore, germination characteristics of the populations studied may have been selected to colonize specific environments at different soil water conditions.

A gene encoding an abscisic acid biosynthetic enzyme (LsNCED4) collocates with the high temperature germination locus Htg6.1 in lettuce (Lactuca sp.).

Thermoinhibition, or failure of seeds to germinate when imbibed at warm temperatures, can be a significant problem in lettuce (Lactuca sativa L.) production. The reliability of stand establishment would be improved by increasing the ability of lettuce seeds to germinate at high temperatures. Genes encoding germination- or dormancy-related proteins were mapped in a recombinant inbred line population derived from a cross between L. sativa cv. Salinas and L. serriola accession UC96US23. This revealed several candidate genes that are located in the genomic regions containing quantitative trait loci (QTLs) associated with temperature and light requirements for germination. In particular, LsNCED4, a temperature-regulated gene in the biosynthetic pathway for abscisic acid (ABA), a germination inhibitor, mapped to the center of a previously detected QTL for high temperature germination (Htg6.1) from UC96US23. Three sets of sister BC3S2 near-isogenic lines (NILs) that were homozygous for the UC96US23 allele of LsNCED4 at Htg6.1 were developed by backcrossing to cv. Salinas and marker-assisted selection followed by selfing. The maximum temperature for germination of NIL seed lots with the UC96US23 allele at LsNCED4 was increased by 2–3°C when compared with sister NIL seed lots lacking the introgression. In addition, the expression of LsNCED4 was two- to threefold lower in the former NIL lines as compared to expression in the latter. Together, these data strongly implicate LsNCED4 as the candidate gene responsible for the Htg6.1 phenotype and indicate that decreased ABA biosynthesis at high imbibition temperatures is a major factor responsible for the increased germination thermotolerance of UC96US23 seeds.Electronic supplementary materialThe online version of this article (doi:10.1007/s00122-010-1425-3) contains supplementary material, which is available to authorized users.