Seed production and pre-dispersal reproductive losses in the narrow endemic <Emphasis Type="Italic">Euphorbia pedroi</Emphasis> (Euphorbiaceae)

Euphorbia pedroi is a narrow endemic species with three known populations located in coastal areas of western Portugal. This study focused on the reproductive biology of this species from flowering to dispersal, aiming to identify the factors causing decrease in seed production potential and to assess the spatio-temporal patterns of seed production at the individual and population levels. The abortion of reproductive structures, particularly seeds, represented a major fraction of losses in the potential seed production of E. pedroi. Moth larvae destroyed a variable proportion of cyathia in a large number of plants from the two populations regardless of their degree of isolation. Furthermore, generalist and specialist pre-dispersal seed predators were responsible for temporally variable seed losses unrelated with variables indicative of plant size and fecundity, and showing no consistency at the individual level. Specialist seed-wasps inflicted the highest losses to E. pedroi and their impact was intimately associated with the magnitude of yearly variation in seed production. This finding highlights the role of the inter-annual variation in seed production as a key feature in this plant-seed predator system. The effect of the two groups of seed predators on the reproductive output of E. pedroi was additive and those insects do not seem to exert an important selective pressure on the traits studied. The proportion of intact seeds produced by E. pedroi differed between locations, but not between individuals within each population, highlighting the major contribution of larger plants to the seed pool.     

Plant fecundity and pre-dispersal reproductive losses in a common and a rare Euphorbia species (Euphorbiaceae)

Comparative studies on the reproductive biology of closely related plant species have provided valuable information to understand the causes and consequences of common-rare differences with possible applications for the management of threatened populations. The magnitude and spatiotemporal variability of seed production and pre-dispersal reproductive losses were studied for 3 years in the rare endemic Euphorbia welwitschii and in its widespread congener E. characias. The factors responsible for a decrease in potential seed production in these species were the lack of a functional ovary in the cyathium, ovary and fruit abortion, seed predation by insects and seed abortion. In E. characias, the moth Acroclita subsequana was also responsible for minor reproductive losses. The proportion of male cyathia varied significantly between seasons, populations and species, being consistently higher in E. characias than in E. welwitschii. Reproductive losses that resulted in ovary, fruit and seed abortion affected mostly the endemic species and were heavier in the populations located near the sea due to local adverse climatic conditions. Seed predators inflicted higher reproductive losses to the endemic species than to its widespread congener and their impact was particularly heavy at Risco. The two Euphorbia species differed markedly in cyathia production, with E. welwitschii producing systematically a lower number of cyathia than its widespread congener and this, together with higher levels of ovary, fruit and seed abortion, seemed to be the main reasons for the low reproductive output of this rare species.     

Variation in floral morphology and individual fecundity in Erythronium dens-canis (Liliaceae)

This study investigated the extent to which the reproductive success of plants of Erythronium dens-canis (Liliaceae), a spring herb of mountain habitats, is dependent on floral morphology. To this end, a series of studies was performed in an area in northwest Spain. The results show that E. dens-canis plants in this area a) are self-compatible, b) need pollinator visits (largely Bombus terrestris and Andrena spp.) to produce seed, and c) show high fruit set under natural conditions. Only 20% of among-plant variance in floral morphology variables was explained by variation in plant size. Floral morphology variables (outer tepal length, stamen length, style length and ovule number) tend to vary in parallel, indicating the existence of an "integrated floral phenotype". Two floral morphology variables (initial number of ovules and outer tepal length) had statistically significant or near-significant effects on seed production. A more detailed experimental analysis indicated that small-flowered plants produce fewer seeds than large-flowered plants, and that this is attributable to less efficient pollination of small flowers. The results of this study thus suggest that among-plant variation in floral morphology in E. dens-canis has implications for reproductive success.     

Effects of Local Plant Density and Incomplete Dichogamy on the Reproductive Success of the Rare Neotropical Palm Geonoma epetiolata

Density dependent processes are known to influence reproduction and establishment of plant populations. In this study, we evaluated the effects of local density and sexual expression on the reproductive success of the rare palm species Geonoma epetiolata in Costa Rica. We classified individuals in two density categories based on distances to the two nearest neighbors and recorded the occurrence of sexual overlap on each individual. Overlap between pistillate and staminate flowers in monoecious plants allows geitonogamous pollination, potentially reducing dependence on mates for reproduction. We measured plant size and light availability, and evaluated the influence of these variables on pollination success, fruit production, fruit abortion and seed mass. Pollination success significantly increased with density but there was no effect of sexual overlap. In contrast, there was no effect of density on the probability of initiated fruit, and a negative effect on fruit set. Fruit abortion was lowest in isolated plants with no sexual overlap. Plant size and light did not contribute to variation in reproductive success. In conclusion, the pollination advantage of plants in dense neighborhoods does not compensate reproductive losses incurred by fruit abortion, possibly due to mating among genetically related individuals. Geonoma epetiolata is threatened by habitat loss and poaching of seeds for the horticultural market. High fruit abortion rates associated with density in G. epetiolata suggest that seed collections from the remnant wild populations of this palm species may cause bottlenecks that further threaten population viability.     

Lifetime fecundity and floral variation in Tuberaria guttata (Cistaceae), a Mediterranean annual

In Tuberaria guttata, petal length, ovule number, and seeds per capsule raised steeply with increasing plant size (respectively, in the ranges 6-11 mm, 40-100, and 20-80), while the number of stamens varied relatively little (14-20). All flowers set fruit, and the rates of embryo abortion were independent of plant size and low on average. Individual fecundities had a markedly right-skewed frequency distribution (in the ranges 1-20 capsules and 20-1500 seeds per plant), which issued not only from plant size and flower production being positively correlated, but also from per-flower ovule numbers being directly proportional to plant size. Correlated variation of plant and ovary sizes amplified among-plant inequalities regarding fecundity; allowed larger plants to set ca. 50% more seed than expected on the basis of flower number only; and caused the slope of the size-fecundity relationship to be considerably steeper (at the population level) than if ovule number was a fixed trait. Corolla, ovary and androecium plasticity in Tuberaria are discussed in terms of environmental effects and developmental constraints.     

Characterizing the interaction between the bogus yucca moth and yuccas: do bogus yucca moths impact yucca reproductive success?

Yucca moths are most well known for their obligate pollination mutualism with yuccas, where pollinator moths provide yuccas with pollen and, in exchange, the moth larvae feed on a subset of the developing yucca seeds. The pollinators, however, comprise only two of the three genera of yucca moths. Members of the third genus, Prodoxus, are the bogus yucca moths and are sister to the pollinator moths. Adult Prodoxus lack the specialized mouthparts used for pollination and the larvae feed on plant tissues other than seeds. Prodoxus larvae feed within the same plants as pollinator larvae and have the potential to influence yucca reproductive success directly by drawing resources away from flowers and fruit, or indirectly by modifying the costs of the mutualism with pollinators. We examined the interaction between the scape-feeding bogus yucca moth, Prodoxus decipiens, and one of its yucca hosts, Yucca filamentosa, by comparing female reproductive success of plants with and without moth larvae. We determined reproductive success by measuring a set of common reproductive traits such as flowering characteristics, seed set, and seed germination. In addition, we also quantified the percent total nitrogen in the seeds to determine whether the presence of larvae could potentially reduce seed quality. Flowering characteristics, seed set, and seed germination were not significantly different between plants with and without bogus yucca moth larvae. In contrast, the percent total nitrogen content of seeds was significantly lower in plants with P. decipiens larvae, and nitrogen content was negatively correlated with the number of larvae feeding within the inflorescence scape. Surveys of percent total nitrogen at three time periods during the flowering and fruiting of Y. filamentosa also showed that larval feeding decreased the amount of nitrogen in fruit tissue. Taken together, the results suggest that although P. decipiens influences nitrogen distribution in Y. filamentosa, this physiological effect does not appear to impact the female components of reproductive success.     

Morphological development of normal and phyllody expressing Rosa hybrida cv. Motrea flowers

A large number of soybean (Glycine max L. Merr.)flowers and young pods abscise rather than develop into mature pods. Flower andpod drop or abortion accounts for the majority of total reproductive abscissionand influences potential soybean yield. The objectives of this study were todetermine the patterns of flower, pod and seed development under treatmentswiththe growth regulators, 2-(2,4-dichlorophenoxy) propanoic acid (2,4-DP) and6-benzylaminopurine (BAP), applied at the early reproductive stages, and toexamine the association of reproductive abscission with growth characteristicsand agronomic traits, including seed yield and seed weight. Small seeded [cvPungsan (11.1±0.4 g100-seed^–1)] and large seeded [cv Manlee(21.0±0.5 g 100-seed^–1)]genotypes were separately planted in the greenhouse and field, and treated witheither 2,4-DP or BAP. 2,4-DP (a synthetic auxin) and BAP (a syntheticcytokinin)were each applied at three concentrations (i.e. high, intermediate or low):0.12mM, 0.08 mM, 0.04 mM, and 1.5mM, 1 mM, 0.5 mM respectively. High andlow concentrations were employed for greenhouse experiments to examine thenumber of flowers per plant in pots. With the exception of low BAP (0.5mM) treatment in Pungsan, all treatments increased total podnumberwith various numbers of seeds per pod. Low 2,4-DP (0.04 mM) inbothgenotypes or BAP (0.5 mM) in Manlee significantly reduced flowerabortion and delayed abscission of pods in both genotypes, resulting inincreased pod setting rates. Under field conditions using intermediateconcentrations, 1 mM BAP significantly increased 100-seed weightto22.3 g at R1 in Manlee and 11.9 g at R3 in Pungsan.BAP (1 mM) at R3 in Pungsan significantly improved seed yield(40.1g plant^–1). Maturity was not significantlyaffected by either application in Manlee, but was significantly affected by BAPin Pungsan. In Pungsan, 2,4-DP increased pod number, plant height and nodenumber, but decreased 100-seed weight in Pungsan treated at R1, causing nosignificant change of seed yield. This study suggested that exogenousregulatorssignificantly influenced reproductive and growth characteristics, andconsequently seed yield, but increase of pod number was not always beneficialfor seed yield.     

Sink strength manipulation in branches of a Mediterranean woody plant suggests sink-driven allocation of biomass in fruits but not of nutrients in seeds

The relative autonomy of branches within an individual plant may favor different resource allocation responses after reproductive losses. The assessment of these reproductive strategies at the branch level before their integration at the plant level would provide more insight into how plants deal with reproductive losses. Here, we present a field experiment to assess changes in the allocation strategies at the branch level after sink strength manipulation in a Mediterranean woody plant (Cistus ladanifer). We applied three levels of removal of developing fruits (75, 25 and 0 %) on branches of the same plants, and measured their effects on resource allocation (biomass, nitrogen and phosphorus) and seed production after controlling for the effects of branch diameter and leaf weight per branch. Our results suggest that after experimental fruit thinning, C. ladanifer branches presented a sink-driven allocation of biomass to fruits but this was not the case for the allocation of nutrients to seeds, which could be driven by competition with leaf biomass. Reductions in biomass per fruit resulted in a reduction in seed output since the average weight per seed remained constant. From these results, it could be suggested that an heterogeneous distribution of fruit losses among the branches within a crown would produce a higher impact on reproductive output than a more equitable distribution.     

Effects of forest age and disturbance on population persistence in the understory herb,Arisaema triphyllum (Araceae)

Long-lived understory herbs experience a highly dynamic forest over space and time, yet can persist for more than a century. To understand how these populations persist, we examined effects of forest age and disturbance on potential sexual reproduction and clonal growth in the sexually labile perennial, Arisaema triphyllum. Potential sexual reproduction (female:male ratio) was significantly greater in the Young and Old-Gap forest states compared with Old, closed-canopy sites, where it was virtually absent. In contrast, clonal growth (estimated by cormlet production) did not differ significantly among the three forest states. Of seven environmental variables measured, only light (positively) and plant density (negatively) contributed significantly to the variation in potential sexual reproduction, while no measured variables contributed significantly to the variation in number of cormlets. The larger sexual reproductive effort (flower+stalk biomass/total biomass) for males in the undisturbed, 100 yr old forest may explain the absence of females in these sites, while the invariant vegetative reproductive effort (cormlet biomass/total biomass) may explain the similarity in average number of cormlets per individual per season across forest states. These results suggest that potential sexual reproduction is resource-limited, while clonal growth may be resource-independent. By maintaining ramet production during unfavorable periods, A. triphyllum populations disperse temporally, waiting for conditions under which sexual reproduction may resume.     

Variation in Predispersal Losses in Reproductive Potential in Rowan (<Emphasis Type="Italic">Sorbus aucuparia</Emphasis> L. Rosaceae) in the NW Iberian Peninsula

We identified the principal factors causing losses in reproductive potential (i.e. quantity of potentially dispersable seeds) over the predispersal period of the reproductive cycle of Sorbus aucuparia L. (Rosaceae) in various populations in the NW Iberian Peninsula. Over the period 1999–2002 we examined the magnitude and variability of losses observed in each stage from bud production to seed production (i.e. bud to flower, flower to initiated fruit, initiated to full-size fruit, and full-size to mature fruit). We also investigated spatial and temporal variation in these losses. Reproductive potential showed very significant losses over the predispersal period in all 4 years: in no case did the number of mature fruits available for dispersal exceed 20% of the initial number of flower buds. In all 4 years of study, we detected statistically significant variation among populations in total losses. The principal cause of loss of reproductive potential over the predispersal period in our Sorbus aucuparia populations was non-initiation of fruit. The plant’s interactions with predispersal predators of buds and seeds show high spatial and temporal variability. Also, the proportions of loss due to the different components did not show within-individual consistency over time. It thus seems unlikely that the different factors contributing to predispersal losses in rowan are currently generating significant selective pressures in our study populations.     

Agronomic evaluation of tissue-culture-derived soybean plants

Summary Genetic alterations of regenerated plants based on the tissue culture process (somaclonal variation) have become common for many plant species including soybean [Glycine max (L.) Merr.]. The objective of this study was to test for the presence of tissue-culture-derived genetic variation in eight agronomic traits in homozygous progeny regenerated by organogenesis using the commercially important cultivar Asgrow A3127. A total of 86 lines derived by repeated self-pollination of nine regenerated plants was grown in two locations for 2 years. When compared to the unregenerated parent, statistically significant variation (P<0.05) was found for maturity, lodging, height, seed protein and oil, but not for seed quality, seed weight, or seed yield. All of the variation noted was beneficial and did not involve decreased yield. Since the differences were not large, the results indicate that the tissue culture process is not necessarily detrimental to plant performance, which is an important consideration since tissue culture techniques are used in many genetic engineering methods.     

Early-acting inbreeding depression and reproductive success in the highbush blueberry,Vaccinium corymbosum L.

Summary Tetraploid Vaccinium corymbosum genotypes exhibit wide variability in seed set following self- and cross-pollinations. In this paper, a post-zygotic mechanism (seed abortion) under polygenic control is proposed as the basis for fertility differences in this species. A pollen chase experiment indicated that self-pollen tubes fertilize ovules, but are also outcompeted by foreign male gametes in pollen mixtures. Matings among cultivars derived from a pedigree showed a linear decrease in seed number per fruit, and increase in seed abortion, with increasing relatedness among parents. Selfed (S₁) progeny from self-fertile parents were largely self-sterile. At zygotic levels of inbreeding of F>0.3 there was little or no fertility, suggesting that an inbreeding threshold regulates reproductive success in V. corymbosum matings. Individuals below the threshold are facultative selfers, while those above it are obligate outcrossers. Inbreeding also caused a decrease in pollen viability, and reduced female fertility more rapidly than male fertility. These phenomena are discussed in terms of two models of genetic load: (1) mutational load — homozygosity for recessive embryolethal or sub-lethal mutations and (2) segregational load — loss of allelic interactions essential for embryonic vigor. Self-infertility in highbush blueberries is placed in the context of late-acting self-incompatibility versus early-acting inbreeding depression in angiosperms.     

Differential costs of reproduction in females and hermaphrodites in a gynodioecious plant

Background and Aims

Plants exhibit a variety of reproductive systems where unisexual (females or males) morphs coexist with hermaphrodites. The maintenance of dimorphic and polymorphic reproductive systems may be problematic. For example, to coexist with hermaphrodites the females of gynodioecious species have to compensate for the lack of male function. In our study species, Geranium sylvaticum, a perennial gynodioecious herb, the relative seed fitness advantage of females varies significantly between years within populations as well as among populations. Differences in reproductive investment between females and hermaphrodites may lead to differences in future survival, growth and reproductive success, i.e. to differential costs of reproduction. Since females of this species produce more seeds, higher costs of reproduction in females than in hermaphrodites were expected. Due to the higher costs of reproduction, the yearly variation in reproductive output of females might be more pronounced than that of hermaphrodites.

Methods

Using supplemental hand-pollination of females and hermaphrodites of G. sylvaticum we examined if increased reproductive output leads to differential costs of reproduction in terms of survival, probability of flowering, and seed production in the following year.

Key Results

Experimentally increased reproductive output had differential effects on the reproduction of females and hermaphrodites. In hermaphrodites, the probability of flowering decreased significantly in the following year, whereas in females the costs were expressed in terms of decreased future seed production.

Conclusions

When combining the probability of flowering and seed production per plant to estimate the multiplicative change in fitness, female plants showed a 56 % and hermaphrodites showed a 39 % decrease in fitness due to experimentally increased reproduction. Therefore, in total, female plants seem to be more sensitive to the cost of reproduction in terms of seed fitness than hermaphrodites.     

Pollinator community structure and sources of spatial variation in plant–pollinator interactions in <Emphasis Type="Italic">Clarkia xantiana</Emphasis> ssp. <Emphasis Type="Italic">xantiana</Emphasis>

The structure of diverse floral visitor assemblages and the nature of spatial variation in plant–pollinator interactions have important consequences for floral evolution and reproductive interactions among pollinator-sharing plant species. In this study, I use surveys of floral visitor communities across the geographic range of Clarkia xantiana ssp. xantiana (hereafter C. x. xantiana) (Onagraceae) to examine the structure of visitor communities, the specificity of the pollination system, and the role of variation in the abiotic vs. biotic environment in contributing to spatial variation in pollinator abundance and community composition. Although the assemblage of bee visitors to C. x. xantiana is very diverse (49 species), few were regular visitors and likely to act as pollinators. Seventy-four percent of visitor species accounted for only 11% of total visitor abundance and 69% were collected in three or fewer plant populations (of ten). Of the few reliable visitors, Clarkia pollen specialist bees were the most frequent visitors, carried more Clarkia pollen compared to generalist foragers, and were less likely to harbor foreign pollen. Overall, the core group of pollinators was obscured by high numbers of incidental visitors that are unlikely to contribute to pollination. In a geographic context, the composition of specialist pollinator assemblages varied considerably along the abiotic gradient spanning the subspecies range. However, the overall abundance of specialist pollinators in plant populations was not influenced by the broad-scale abiotic gradient but strongly affected by local plant community associations. C. x. xantiana populations sympatric with pollinator-sharing congeners were visited twice as often by specialists compared to populations occurring alone. These positive indirect interactions among plant species may promote population persistence and species coexistence by enhancing individual reproductive success.Electronic Supplementary Material Supplementary material is available for this article at     

Genetic diversity and floral dimorphism in Limonium dendroides (Plumbaginaceae), a woody Canarian species on the way of extinction

We combined reproductive and allozyme data to assess the levels and structuring of genetic variation and propose conservation guidelines in Limonium dendroides, a critically endangered Canarian endemic Plumbaginaceae featuring the floral and pollen pap/cob dimorphisms associated with the heteromorphic diallelic self-incompatibility system described for this family. Although seed germination has been reported in greenhouse conditions, the detection of individuals of only one morph in all wild subpopulations surveyed explains the extremely limited seed production and recruitment in nature. The geographical proximity and genetic closeness between some subpopulations, together with absence of inbreeding depression symptoms, and a higher allozyme variation in the cultured or reintroduced offspring than in their parental wild subpopulations indicate the viability of occasional compatible matings, thereby suggesting that even low levels of gene flow could mitigate the deleterious effects of fragmentation on subpopulation survival. However, our overall results indicate that L. dendroides is in a critical conservation situation where the utter scarcity of compatible mates within the subpopulations, radically low subpopulation sizes, poor inter-subpopulation gene flow, impoverished genetic variation, herbivore grazing, and the extreme habitat topography have overridden the reproductive capabilities of the species. According to our results, once morph types in all wild and cultured specimens can be determined, inducing fertile crosses through mixed reinforcements is advisable only in the most extremely isolated and small subpopulations (Argaga and Guarimiar) using individuals from the nearest ones (Azadoe and Palmarejo), whilst non-mixed reinforcements seem viable in the remaining subpopulations. Only when the subpopulations attain higher seed production and recruitment rates will it be adequate to collect seeds for their storage at a germplasm bank facility.     

Ecological correlates of seed mass variation in Phoradendron juniperinum,a xylem-tapping mistletoe

Summary We investigated several ecological correlates of seed mass variation in the hemiparasitic, xylemtapping mistletoe, Phoradendron juniperinum. Mean seed mass varied two-fold among plants between the ages of 4 and 14 years old and was positively correlated with parental plant age. Both the standard deviation and the coefficient of variation in mean seed mass decreased with increasing plant age demonstrating that, on average, younger plants produced seed with more variable mass. Nitrogen concentrations (mg nitrogen per gram of seed) of both the seed and fruit (pericarp) were not correlated with mass or the age of the parent plant from which the seed was taken. However, the nitrogen content per seed (mg nitrogen per seed) was positively correlated with the mean seed dry mass and the age of the seed parent, suggesting that the carbon to nitrogen ratio of individual seeds remained relatively constant as seed mass increased and plants grew older. Seed germination ranged between 20% and 86% and was positively correlated with mass and parental plant age. Heavier seeds (seeds from older plants) also had the highest root radicle growth rates. Furthermore, the final root radicle length after 76 d of growth was positively correlated with seed dry mass. When grown on a medium containing an extract prepared from the host plant foliage, all seeds showed lower germination, grew more slowly and had shorter overall root radicles, but had significantly greater development of the haustorial disks (the holdfast which forms the host-parasite junction in Phoradendron) than seeds grown on a control medium. Our results suggest that, on average, seeds of greater mass produced by older plants have a greater total resource pool per propagule (fruit + seed). This resource pool may be important in conferring a greater potential for dispersal (fruit), survival, colonization, and establishment.     

Salt sensitivity in chickpea (Cicer arietinum L.): ions in reproductive tissues and yield components in contrasting genotypes

The reproductive phase in chickpea (Cicer arietinum L.) is affected by salinity, but little is known about the underlying cause. We investigated whether high concentrations of Na⁺ and Cl^– in the reproductive structures influence reproductive processes. Chickpea genotypes contrasting in tolerance were subjected to 0, 35 or 50 mm NaCl applied to soil in pots. Flower production and abortion, pod number, percentage of empty pods, seed number and size were evaluated. The concentrations of Na⁺, K⁺ and Cl^– were measured in various plant tissues and, using X‐ray microanalysis, in specific cells of developing reproductive structures. Genotypic variation in reproductive success measured as seed yield in saline conditions was associated with better maintenance of flower production and higher numbers of filled pods (and thus seed number), whereas seed size decreased in all genotypes. Despite the variation in reproductive success, the accumulation of Na⁺ and Cl^– in the early reproductive tissues of developing pods did not differ between a tolerant (Genesis836) and a sensitive (Rupali) genotype. Similarly, salinity tolerance was not associated with the accumulation of salt ions in leaves at the time of reproduction or in seeds at maturity.     

Masting behaviour in a Mediterranean pine tree alters seed predator selection on reproductive output

• Context‐dependency in species interactions is widespread and can produce concomitant patterns of context‐dependent selection. Masting (synchronous production of large seed crops at irregular intervals by a plant population) has been shown to reduce seed predation through satiation (reduction in rates of seed predation with increasing seed cone output) and thus represents an important source of context‐dependency in plant‐animal interactions. However, the evolutionary consequences of such dynamics are not well understood.
• Here we describe masting behaviour in a Mediterranean model pine species (Pinus pinaster) and present a test of the effects of masting on selection by seed predators on reproductive output. We predicted that masting, by enhancing seed predator satiation, could in turn strengthen positive selection by seed predators for larger cone output. For this we collected six‐year data (spanning one mast year and five non‐mast years) on seed cone production and seed cone predation rates in a forest genetic trial composed by 116 P. pinaster genotypes.
• Following our prediction, we found stronger seed predator satiation during the masting year, which in turn led to stronger seed predator selection for increased cone production relative to non‐masting years.
• These findings provide evidence that masting can alter the evolutionary outcome of plant‐seed predator interactions. More broadly, our findings highlight that changes in consumer responses to resource abundance represent a widespread mechanism for predicting and understanding context dependency in plant‐consumer evolutionary dynamics.

     

Interval mapping of quantitative trait loci for reproductive,morphological, and seed traits of soybean (Glycine max L.)

Quantitative trait loci (QTL) were mapped in segregating progeny from a cross between two soybean (Glycine max (L.) Merr.) cultivars: Minsoy (PI 27.890) and Noir 1 (PI 290.136). The 15 traits analyzed included reproductive, morphological, and seed traits, seed yield and carbon isotope discrimination ratios (¹³C/¹²C). Genetic variation was detected for all of the traits, and transgressive segregation was a common phenomenon. One hundred and thirty-two linked genetic markers and 24 additional unlinked markers were used to locate QTL by interval mapping and one-way analysis of variance, respectively. Quantitative trait loci controlling 11 of the 15 traits studied were localized to intervals in 6 linkage groups. Quantitative trait loci for developmental and morphological traits (R1, R5, R8, plant height, canopy height, leaf area, etc.) tended to be clustered in three intervals, two of which were also associated with seed yield. Quantitative trait loci for seed oil were separated from all the other QTL. Major QTL for maturity and plant height were linked to RFLP markers R79 (31% variation) and G173 (53% variation). Quantitative trait loci associated with unlinked markers included possible loci for seed protein and weight. Linkage between QTL is discussed in relation to the heritability and genetic correlation of the traits.     

Effects of seed release timing on plant life-history and seed production in a population of a desert annual,shape Blepharis sindica (Acanthaceae)

Growth, phenology, survivorship, and seed production were observed in a population of a desert annual, Blepharis sindica, with reference to the variation in the timing of seedling emergence. The population consisted of several cohorts induced by rain-cued seed release within a growing season. The fate of 100 individuals of six cohorts was monitored throughout the growing season. Earlier-established cohorts had significantly larger plant sizes and higher reproductive outputs than later cohorts. The time and duration of each phenological stage varied among the cohorts, and they were also influenced by plant size. Mortalities at the seedling stage, vegetative stage, and reproductive stage increased with the delay of seed release. Seed release was concentrated in the early growing season. Fecundity was highest in the earliest cohort and decreased monotonically in later cohorts. The results suggested that even in temporally varying environments, the superiority of early emergent plants was evident. The seed release patterns in temporally fluctuating desert environments are discussed as a compromise between 'diversified bet-hedging' and an optimal timing for maximizing the reproductive success in a growing season.