Seed size as an indicator of seed quality: a case study of Primula veris

The Establishment of an Ex Situ Collection of Primula veris in Bulgaria

Primula veris is a valuable medicinal plant species with declining populations, protected in Bulgaria by the Biodiversity Act. The present study aimed to increase its extremely low seed germination rate, starting with seeds originating from two Bulgarian populations, and to set up an ex situ field collection. The stimulation effect of three factors was tested in in vivo and in vitro experiments: seeds treated with gibberellic acid (in different concentrations and exposure time), light quality (white, infrared, red, and blue or dark), and cold stratification. The combination of factors resulted in 36 treatment variants in vivo and 8 treatment variants in vitro. No germination was observed in control treatment variants. The highest germinating rate (95%) was noticed in vivo under blue monochromatic light after seed soaking into 0.2% GA₃ for 10 h; however, the best results (55% of well-developed seedlings) were observed with a combination of blue light and 0.3% GA₃ for 5 h. Seedlings were successfully strengthened in vermiculite in a phytotron, potted in soil and grown in a greenhouse, and then 75 plants were transferred to the field plot, where most of them bloomed at the first vegetation season. These results are intended to serve as a basis for establishing a pilot agriculture of the species.

Germination of Triticum aestivum L.: Effects of Soil–Seed Interaction on the Growth of Seedlings

Seed size, sowing depth, and seed disinfection can affect seed germination and seedling establishment, which, in turn, can directly affect crop growth and yield. The current study was comprised of two experiments, the first of which was conducted in the laboratory, and a second which was performed under glasshouse conditions. The objective of these experiments was to investigate the effects of seed size, sowing depth, and seed disinfection on seed germination and initial seedling growth of selected wheat (Triticum aestivum L.) cultivars. The treatments in laboratory experiment were arranged in a completely randomized design, which included: (Ι) four wheat cultivars (Pishgam, Haydari, Soissons, and Mihan), (ΙΙ) two seed size classes (x < 2.25 mm, and x > 2.25 mm), and two disinfection treatments (no-disinfection and disinfection), (ΙΙΙ) with five replicates. In addition to the aforementioned treatments, the effect of planting depth (4, 6, and 8 cm) was also investigated in the subsequent glasshouse experiment. The best results were obtained at a sowing depth of 4 cm, in the non-disinfected treatment, using large seeds. In contrast, the lowest percentage and speed of seed germination and vigor index were observed in seeds sown at 8 cm depth, in the disinfected seed treatment, using small seeds. Large seeds contain larger nutrient stores which may improve seed germination indices, which would therefore result in improved percentage and speed of seed germination, followed by faster coleoptile and seedling growth, higher seedling dry weight and seed vigor. These data also illustrated that seed disinfection in the Pishgam and Haydari cultivars had inhibitory effects upon coleoptile growth and seedling length, which could be related to the fungicide’s chemical composition. Unlike other cultivars, disinfection did not show a significant effect on the Soissons cultivar. Based on our data, in order to improve both the speed of wheat seed germination and subsequent plant growth and development; it is necessary to select high-quality, large seeds, planted at a specific planting depth, which have been treated with an effective disinfectant; all of which will be specific for the wheat cultivar in question. Overall, the current study has provided useful information on the effect size seed, sowing depth, and disinfection have upon germination characteristics and seedling growth of wheat cultivars, which can form the basis for future field scale trails.

Quantitative Trait Locus Analysis and Identification of Candidate Genes Affecting Seed Size and Shape in an Interspecific Backcross Inbred Line Population of Gossypium hirsutum × Gossypium barbadense

Seed size and shape are key agronomic traits affecting seedcotton yield and seed quality in cotton (Gossypium spp.). However, the genetic mechanisms that regulate the seed physical traits in cotton are largely unknown. In this study, an interspecific backcross inbred line (BIL) population of 250 BC1F7 lines, derived from the recurrent parent Upland CRI36 (Gossypium hirsutum) and Hai7124 (Gossypium barbadense), was used to investigate the genetic basis of cotton seed physical traits via quantitative trait locus (QTL) mapping and candidate gene identification. The BILs were tested in five environments, measuring eight seed size and shape-related traits, including 100-kernel weight, kernel length width and their ratio, kernel area, kernel girth, kernel diameter, and kernel roundness. Based on 7,709 single nucleotide polymorphic (SNP) markers, a total of 49 QTLs were detected and each explained 2.91-35.01% of the phenotypic variation, including nine stable QTLs mapped in at least three environments. Based on pathway enrichment, gene annotation, genome sequence, and expression analysis, five genes encoding starch synthase 4, transcription factor PIF7 and MYC4, ubiquitin-conjugating enzyme E27, and THO complex subunit 4A were identified as candidate genes that might be associated with seed size and shape. Our research provides valuable information to improve seed physical traits in cotton breeding.

Integrating demography and distribution modeling for the iconic Leontopodium alpinum Colm. in the Romanian Carpathians

Both climate change and human exploitation are major threats to plant life in mountain environments. One species that may be particularly sensitive to both of these stressors is the iconic alpine flower edelweiss (Leontopodium alpinum Colm.). Its populations have declined across Europe due to over-collection for its highly prized flowers. Edelweiss is still subject to harvesting across the Romanian Carpathians, but no study has measured to what extent populations are vulnerable to anthropogenic change.Here, we estimated the effects of climate and human disturbance on the fitness of edelweiss. We combined demographic measurements with predictions of future range distribution under climate change to assess the viability of populations across Romania.We found that per capita and per-area seed number and seed mass were similarly promoted by both favorable environmental conditions, represented by rugged landscapes with relatively cold winters and wet summers, and reduced exposure to harvesting, represented by the distance of plants from hiking trails. Modeling these responses under future climate scenarios suggested a slight increase in per-area fitness. However, we found plant ranges contracted by between 14% and 35% by 2050, with plants pushed into high elevation sites.Synthesis. Both total seed number and seed mass are expected to decline across Romania despite individual edelweiss fitness benefiting from a warmer and wetter climate. More generally, our approach of coupling species distribution models with demographic measurements may better inform conservation strategies of ways to protect alpine life in a changing world.

Evaluating the fitness effects of seed size and maternal tree size on Polylepis tomentella (Rosaceae) seed germination and seedling performance

In vascular plants, larger seeds are generally associated with higher germination potential, healthier seedlings and overall higher rates of survivorship. How this relationship holds or what other physiological tradeoffs evolved in plants adapted to high-altitude environments, such as the tropical and subtropical highland Polylepis tree, remain unclear. In this study, we evaluated the relationship between seed mass and seedling performance by testing the reserve effect, the metabolic effect, and the seedling-size effect hypotheses in Polylepis tomentella Weddell (Rosaceae). Since the relationship between fitness and seed size can often depend on maternal plant size, we additionally investigated the association between germination success, seedling performance (survival, relative growth rate (RGR) and height), and size of bearing-seed trees under controlled greenhouse conditions. Our results showed that heavier seeds are more likely to germinate, but we did not find evidence that could support the reserve effect, metabolic effect or seedling-size effect. As seedlings from larger and medium seeds exhibited comparatively similar RGR, survival percentages and final size, maternal plant size was positively associated with improved seed quality and seedling performance. These results demonstrate that seed mass and maternal size during early seedling establishment are critical for Polylepis persistence, demography and conservation.

Effects of ten years organic and conventional farming on early seedling traits of evolving winter wheat composite cross populations

Early vigour traits of wheat composite cross populations (CCPs) based on high yielding (Y) or high quality (Q) or Y*Q varietal intercross evolving under organic or conventional conditions in parallel populations were studied hydroponically. To eliminate storage and year effects, frozen F6, F10, F11 and F15 seeds were multiplied in one field, resulting in the respective Fx.1 generations. This eliminated generation and growing system effects on seed size for the F6.1 F10.1 and F15.1. Due to a severe winter kill affecting the F11, the generation effect persisted, leading to larger seeds and markedly different seedling traits in the F11.1 compared to the F10.1 and F15.1. Seedling traits were similar among parallel populations. Shoot length and weight increased in both systems until the F11.1 across farming systems and remained constant thereafter. Over time, seminal root length and root weight of organic CCPs increased and total- and specific- root length decreased significantly compared to the conventional CCPs. Rooting patterns under organic conditions suggests better ability to reach deeper soil nutrients. In both systems, Q and YQ CCPs were more vigorous than Y CCPs, confirming genetic differences among populations. Overall, heterogeneous populations appear very plastic and selection pressure was stronger in organic systems.

A multi-level test of the seed number/size trade-off in two Scandinavian communities

Seed size is a fundamental life-history trait for plants. A seed number/size trade-off is assumed because the resources invested in reproduction are limited; however, such a trade-off is not always observed. This could be a consequence of the method used for testing it, where the null hypothesis is dictated by common statistical practice, rather than being based on any underlying theory. Alternatively, there might be some population- and species-dependent variables that affect resource availability and, in turn, influence the presence and intensity of this trade-off. Using data on 42 herbs from two communities (lowland and alpine) from Southern Norway, we tested the validity of the classical linear model vs. two previously proposed models, based on resource competition, when assessing the existence of this trade-off at different levels. We also evaluated whether some species- (fruit aggregation, ovules/flower) and population-dependent (pollen limitation) variables could affect this trade-off. Classical linear modelling outperformed the other proposed functional models. Significant seed number/size relationships were negative in single-fruited species, whereas they were positive in species with infructescences of one-seeded fruits. Concordantly, fruit organization was the most influencing variable for the intra-specific trade-off in the lowland community. In the alpine community, species suffering higher pollen limitation showed more strongly negative slopes between seed size and seed number at the fruit/infructescence level. Across species, seed size and number were negatively related, although the relationship was significant in only one of the communities. No evidence of trade-off was found at the plant level. Linear models provide a flexible framework that allows coping with the variability in the seed number/size relationship. The emergence of the intra-specific relationship between seed number and size depends on species- and population-dependent variables, related to resource allocation and the pollination environment.

Acorn size and tolerance to seed predators: the multiple roles of acorns as food for seed predators, fruit for dispersal and fuel for growth

Fitness of parents and offspring is affected by offspring size. In oaks (Quercus spp.), acorns vary considerably in size across, and within, species. Seed size influences dispersal and establishment of oaks, but it is not known whether size imparts tolerance to seed predators. Here, we examine the relative extent to which cotyledon size serves as both a means for sustaining partial consumption and energy reserves for developing seedlings during early stages of establishment. Acorns of 6 oak species were damaged to simulate acorn predation by vertebrate and invertebrate seed predators. Seedling germination/emergence and growth rates were used to assess seedling performance. We predicted that if cotyledons are important for dispersal, acorns should show tolerance to partial seed consumption. Alternatively, if the cotyledon functions primarily as an energy reserve, damage should significantly influence seedling performance. Acorns of each species germinated and produced seedlings even after removing >50% of the cotyledon. Seed mass explained only some of the variation in performance. Within species, larger acorns performed better than smaller acorns when damaged. Undamaged acorns performed as well or better than damaged acorns. There was no pattern among individual species with increasing amounts of damage. In some species, simulated invertebrate damage resulted in the poorest performance, suggesting alternative strategies of oaks to sustain damage. Large cotyledons in acorns may be important for attracting seed dispersers and sustaining partial damage, while also providing energy to young seedlings. Success of oak establishment may follow from the resilience of acorns to sustain damage at an early stage.

Flower power: Floral and resource manipulations reveal how and why reproductive trade-offs occur for lowbush blueberry (Vaccinium angustifolium)

Plant reproductive trade-offs are thought to be caused by resource limitations or other constraints, but more empirical support for these hypotheses would be welcome. Additionally, quantitative characterization of these trade-offs, as well as consideration of whether they are linear, could yield additional insights. We expanded our flower removal research on lowbush blueberry (Vaccinium angustifolium) to explore the nature of and causes of its reproductive trade-offs. We used fertilization, defoliation, positionally biased flower removal, and multiple flower removal levels to discern why reproductive trade-offs occur in this taxon and to plot these trade-offs along two continuous axes. We found evidence through defoliation that vegetative mass per stem may trade off with reproductive effort in lowbush blueberry because the two traits compete for limited carbon. Also, several traits including ripe fruit production per reproductive node and fruit titratable acidity may be "sink-limited"-they decline with increasing reproductive effort because average reproductive structure quality declines. We found no evidence that reproductive trade-offs were caused by nitrogen limitation. Use of reproductive nodes remaining per stem as a measure of reproductive effort indicated steeper trade-offs than use of the proportion of nodes remaining. For five of six traits, we found evidence that the trade-off could be concave down or up instead of strictly linear. Synthesis. To date, studies have aimed primarily at identifying plant reproductive trade-offs. However, understanding how and why these trade-offs occur represent the exciting and necessary next steps for this line of inquiry.

The presence of a below-ground neighbour alters within-plant seed size distribution in Phaseolus vulgaris

BACKGROUND AND AIMS

Considerable variation in seed size commonly exists within plants, and is believed to be favoured under natural selection. This study aims to examine the extent to which seed size distribution depends on the presence of competing neighbour plants.

METHODS

Phaseolus vulgaris plants rooting with or without a conspecific neighbour were grown in soil with high or low nutrient availability. Seeds were harvested at the end of the growth cycle, the total nitrogen and phosphorus invested in seed production were measured and within-plant seed size distribution was quantified using a set of statistical descriptors.

KEY RESULTS

Exposure to neighbours' roots induced significant changes in seed size distribution. Plants produced proportionally more large seeds and fewer small ones, as reflected by significant increases in minimal seed size, mean seed size, skewness and Lorenz asymmetry coefficient. These effects were different from, and in several cases opposite to, the responses when the soil nutrient level was reduced, and were significant after correction for the amount of resources invested in seed production.

CONCLUSIONS

Below-ground neighbour presence affects within-plant seed size distribution in P. vulgaris. This effect appears to be non-resource-mediated, i.e. to be independent of neighbour-induced effects on resource availability. It implies that, based on current environmental cues, plants can make an anticipatory adjustment of their investment strategy in offspring as an adaptation to the local environment in the future.

Massa das sementes de Tecoma stans L. Juss. ex Kunth (Bignoniaceae): efeitos na emergência e desenvolvimento de suas plântulas no sol e na sombra

Este estudo teve como objetivo avaliar o efeito da massa das sementes de Tecoma stans L. Juss. ex Kunth na emergência, no crescimento e no desenvolvimento inicial de suas plântulas sob diferentes condições de luminosidade. As sementes foram separadas em quatro classes de massa e semeadas em quatro réplicas de 24 sementes para cada classe, no sol e na sombra. No ambiente de sol ocorreu a maior porcentagem de emergência. Dentre as classes de massa, sementes maiores apresentaram maior porcentagem de emergência em ambos os ambientes, porém a maior velocidade foi observada na sombra. Após um mês do início do experimento as plântulas da sombra apresentaram 100% de mortalidade. O crescimento e desenvolvimento das plântulas no sol foram acompanhados mensalmente por um período de cinco meses. Neste período, foi possível observar os efeitos da massa das sementes de Tecoma stans no ganho de massa seca das plântulas nos três primeiros meses; a partir deste, a massa das sementes não teve efeito no ganho de matéria seca pelas plântulas. A partição da biomassa das plântulas não diferiu entre as classes de massa testadas. As plântulas de menor massa apresentaram uma tendência a uma maior área foliar específica em relação às plântulas originárias de sementes mais pesadas, principalmente nos três primeiros meses, resultando em um ganho maior de matéria seca das plântulas de menor classe de massa. Já no quarto mês, a área foliar específica não apresentou qualquer tendência. O fato de sementes maiores originarem plântulas com melhor desenvolvimento inicial quando comparadas com as sementes menores pode ser considerada como estratégia reprodutiva da espécie, assim como produzir sementes de diversos tamanhos pode ser considerado como uma maneira da espécie dispersar-se e colonizar um maior número de microambientes.

Seeds of alpine plants are short lived: implications for long-term conservation

BACKGROUND AND AIMS

Alpine plants are considered one of the groups of species most sensitive to the direct and indirect threats to ecosystems caused by land use and climate change. Collecting and banking seeds of plant species is recognized as an effective tool for providing propagating material to re-establish wild plant populations and for habitat repair. However, seeds from cold wet environments have been shown to be relatively short lived in storage, and therefore successful long-term seed conservation for alpine plants may be difficult. Here, the life spans of 69 seed lots representing 63 related species from alpine and lowland locations from northern Italy are compared.

METHODS

Seeds were placed into experimental storage at 45 °C and 60 % relative humidity (RH) and regularly sampled for germination. The time taken in storage for viability to fall to 50 % (p(50)) was determined using probit analysis and used as a measure of relative seed longevity between seed lots.

KEY RESULTS

Across species, p(50) at 45 °C and 60 % RH varied from 4·7 to 95·5 d. Seed lots from alpine populations/species had significantly lower p(50) values compared with those from lowland populations/species; the lowland seed lots showed a slower rate of loss of germinability, higher initial seed viability, or both. Seeds were progressively longer lived with increased temperature and decreased rainfall at the collecting site.

CONCLUSIONS

Seeds of alpine plants are short lived in storage compared with those from lowland populations/related taxa. The lower resistance to ageing in seeds of alpine plants may arise from low selection pressure for seed resistance to ageing and/or damage incurred during seed development due to the cool wet conditions of the alpine climate. Long-term seed conservation of several alpine species using conventional seed banking methods will be problematic.

Long-term variation in seed mass and seed production in populations of Paris quadrifolia

Seed production of the perennial herb Paris quadrifolia L. (Liliaceae) was investigated in five populations in northern Poland. The long-term seed production per square metre differed significantly among populations and years. Moreover, throughout the 7-year study period, 30% of both whole ripe fruits and seeds alone were predated. Variation in seed mass per fruit in both space and time was significant. Throughout the 7-year study, nearly all the marked individuals produced fruits once every 2 years. The most frequent break between fruiting was 2 years and the longest was 5 years. Only the mean seed mass in fruits of the same individual varied significantly over subsequent years. In the five populations, the number of ovules, number of seeds in the fruit and seed mass varied significantly between populations. However seed/ovule ratio did not differ in fruits in the five populations. The seed mass/number trade-off in fruits was strongly partially correlated when the effect of total seed mass was considered. Breeding experiments suggest that P. quadrifolia has a substantial capacity for both inbreeding and outbreeding. There were no significant differences in the seed/ovule ratio, seed number or seed mass in fruits produced from bagged or control flowers. However, both seed/ovule ratio and number of seeds were significantly lower in fruits from emasculated flowers.

Effects of pollination timing on seed paternity and seed mass in Silene latifolia (Caryophyllaceae)

BACKGROUND AND AIMS

Competition among genetically different pollen donors within one recipient flower may play an important role in plant populations, increasing offspring genetic diversity and vigour. However, under field conditions stochastic pollen arrival times may result in disproportionate fertilization success of the first-arriving pollen, even to the detriment of the recipient plant's and offspring fitness. It is therefore critical to evaluate the relative importance of arrival times of pollen from different donors in determining siring success.

METHODS

Hand pollinations and genetic markers were used to investigate experimentally the effect of pollination timing on seed paternity, seed mass and stigmatic wilting in the the dioecious plant Silene latifolia. In this species, high prevalence of multiply-sired fruits in natural populations suggests that competition among different donors may often take place (at fertilization or during seed development); however, the role of variation due to pollen arrival times is not known.

KEY RESULTS

First-arriving pollen sired significantly more seeds than later-arriving pollen. This advantage was expressed already before the first pollen tubes could reach the ovary. Simultaneously with pollen tube growth, the stigmatic papillae wilted visibly. Individual seeds were heavier in fruits where one donor sired most seeds than in fruits where both donors had more even paternity shares.

CONCLUSIONS

In field populations of S. latifolia, fruits are often multiply-sired. Because later-arriving pollen had decreased chances of fertilizing the ovules, this implies that open-pollinated flowers often benefit from pollen carry-over or pollinator visits within short time intervals, which may contribute to increase offspring genetic diversity and fitness.