Sylleptic branching in winter-headed apple (<Emphasis Type="Italic">Malus × domestica)</Emphasis> trees: accession-dependent responses and their relationships with other tree architectural characteristics

Well-feathered apple trees are essential for commercial orchards to optimize yields. However, most cultivars do not form these sylleptic branches readily in commercial nurseries due to high apical dominance. Several treatments exist to promote their formation in the nurseries, one of which is heading. However, not all cultivars are expected to react similarly to these treatments. We studied the branching response of 155 genotypes following heading and its relation to other architectural traits as a function of the cultivar’s genetic background. Trees were grown for two consecutive years after grafting in a nursery, and the main axes were headed in the winter following growth in year 1. After heading, a single shoot was retained when growth resumed in the second year. Plant architectural traits such as growth of the main shoot, internode length, sylleptic branching, etc. were measured before and after heading and were statistically compared using a mixed model. This model showed the effect of heading for all architectural traits studied. In addition significant genotype and genotype × treatment interactions were found. In general, genotypes that showed a more vigorous growth during the first year also reacted more vigorously to heading. Accounting for the genetic substructure of this collection, no clear distinction in tree response could be found except in a small group of individuals that belonged to an F1 mapping population. This study shows that heading is not favorable for all genotypes to promote sufficient sylleptic branching and that other methods are needed to promote branching in these accessions.     

Size and architectural traits as ontogenetic determinants of fitness in a phenotypically plastic annual weed (Amaranthus albus)

Abstract Plasticity of size and architectural traits, and their importance to reproductive fitness, were estimated in relation to nutrient availability in the annual Amaranthus albus . Seeds from seven field-collected genotypes were used to rear a first generation under uniform conditions. Seed families (inbred lines) from four first-generation plants per genotype were used to rear a second generation in a glasshouse for 10 weeks. Nine plants per family were regularly fertilized, while nine others were unfertilized. Size was estimated at 5, 8, and 10 weeks; architectural traits were recorded at 8 weeks (no. branches) and 10 weeks (no. branches and branch length). Fitness was assessed by the number of seeds per plant. Because traits were intercorrelated, size-scaled architectural traits were generated and allometric analyses performed. Genetic variation was analyzed for the second generation among inbred lines of the original genotypes, and among families within each genotype. For fertilized and unfertilized groups, early size (volume occupied at 5 weeks) and branch length per mass were significant determinants of fitness. The number of branches per size explained a smaller proportion of the variance in fitness. Genotype by treatment interaction was apparent for some traits, indicating genetic variation for plasticity, but plasticity of size did not change over ontogeny. Significant effects of genotype on size and architectural traits, and fitness, were detected mostly in the unfertilized group. Thus, selection is most likely to differentiate among genotypes in nutrient-poor environments. Lengthening of multiple branches increases seed output throughout the season, and genotypes with longer branches per unit mass have a selective advantage. Because early size is correlated with seed output, ontogenetic plasticity in response to improved soil resources allows opportunistic increases in fitness.     

ADAPTATION TO FINE-GRAINED ENVIRONMENTAL VARIATION: AN ANALYSIS OF WITHIN-INDIVIDUAL LEAF VARIATION IN AN ANNUAL PLANT

Recent studies of evolution in heterogeneous environments have concentrated on the role of coarse-grained environmental variation. Here I explore the potential for a modular organism to adapt to fine-grained environmental variation through within-individual variation among modules. I describe the pattern of variation among leaves of single individuals and report results of initial analyses of genetic variation for within-individual variability in leaf traits and of genetic correlations that could influence the rate of further evolution of within-individual variation of these traits. Plants from 24 paternal half-sib families were raised in growth chambers, and five traits were measured for two leaves produced by each plant. Four of the five traits differed significantly between sampling times. Genetic analyses revealed significant additive genetic variation for within-individual variation in several traits. Estimates of family mean correlations between traits expressed at different times suggest few relationships that would be expected to impede response to selection for changes in the pattern of within-individual variation in leaf traits. These results support the possibility that within-individual variation could evolve as an adaptive response to fine-grained environmental variation and suggest a need for further investigation to improve understanding of evolution in heterogeneous environments.     

Phenotypic plasticity of introduced versus native purple loosestrife: univariate and multivariate reaction norm approaches

The plastic responses to environmental change by Lythrum salicaria (purple loosestrife) were compared between native plants derived from seeds collected in Europe and those introduced into North America. Plants from nine populations each were grown under two levels of water and nutrient conditions. At the end of the growing season, samples were evaluated for eight traits related to their life history, plant size/architecture, and reproduction. Genetic (G), environmental (E), and G × E interactions were assessed by restricted maximum likelihood (REML) analysis of covariance (ANCOVA) and multivariate analysis of covariance (MANCOVA). Both univariate and multivariate reaction norm analyses were used to test for differences in the magnitude and direction of phenotypic plasticity between introduced and native plants. Under high-nutrient conditions, introduced plants were taller and had more branches and greater aboveground biomass. They also exhibited significantly greater amounts of phenotypic plasticity for aboveground biomass than did the natives in response to changing nutrient levels in standing water. This difference in univariate plasticity contributed to the general contrast in multivariate plasticity between introduced and native plants. These results support the idea that introduced plants may successfully invade a habitat and grow better than native plants in response to increased resources.     

Life history variation in Campanula americana (Campanulaceae): population differentiation

Genetic variation in life history traits has important consequences for life-history evolution. Here we report the results of a greenhouse experiment investigating the broad sense genetic basis of variation in life history traits within and among five populations of Campanula americana distributed along a latitudinal gradient. The populations exhibit differentiation for a number of morphological traits (seed weight, number of branches, final plant size, number of capsules) and the phenological traits, days to emergence, days to bolting, the onset of flowering, and the duration of flowering. Families within populations differed only in days to emergence and seed weight. These results suggest that the life history differences among populations are genetically based. In addition, two life history types—winter annuals and biennials—have previously been reported from natural populations of Campanula americana. This experiment identified a third type—summer annuals from the Florida population.     

Distribution of mineral nutrient from nodal roots of Trifolium repens: Genotypic variation in intra-plant allocation of 32P and 45Ca

To assess genotypic variability in nutrient supply of shoot branches, the distribution of ³²P and ⁴⁵Ca exported from a source nodal root (24-h uptake period) was measured within a genotype of a large-leaved (Kopu) and a small-leaved (Tahora) cultivar of Trifolium repens. Source-sink relationships of plants were modified by root severance, defoliation, and shade treatments. In control plants of both genotypes distribution of ³²P and ⁴⁵Ca closely followed the pathways that could be predicted from the known phyllotactic constraints on the vascular system. As such there was little allocation of radioisotopes (3.1% and 2.5% of exported ³²P and ⁴⁵Ca, respectively) from the source root to branches on the apposite side of the parent axis (far-side branches). However, genotypic differences in nutrient allocation were apparent, when treatments were imposed to alter intra-plant source-sink relationships. In the large-leaved genotype, the imposed treatments had minor effects on the allocation to far-side branches: whereas, in the small-leaved genotype, root severance and defoliation treatments increased lateral transport to far-side branches to 30% (³²P) and 10% (⁴⁵Ca) of exported radioisotopes. Genotypes with low (8–9) and high (12–13) numbers of vascular bundles were selected from within the large-leaved cultivar. Distribution of ³²P was then measured after plants had been pre-treated by removal of all far-side roots two days prior to labelling. Genotypes with low vascular bundle number allocated 20% and those with high vascular bundle number 3.2% of exported ³²P to far-side branches. It was concluded (1) that genotypic variation exists within T. repens for potential to alter intra-plant allocation of mineral nutrients, in response to treatments that modify source-sink relationships within plants; and (2) that this variation is correlated with differences among genotypes in the organisation of the vasculature of their stolons.     

Influence of plant genotype and environment on oviposition preference and offspring survival in a gallmaking herbivore

Summary Plant resistance to insect herbivores may derive from traits influencing herbivore preference, traits influencing the suitability of the plant as a host, or both. However, the plant traits influencing host-plant selection by ovipositing insect herbivores may not completely overlap those traits that affect larval survival, and distinct traits may exhibit different levels of genetic vs. environmental control. Therefore, resource supply to the host plant could affect oviposition preference and larval performance differently in different plant genotypes. To test this hypothesis, the effects of resistance level, plant genotype, and resource supply to the host plant on oviposition preference and larval performance of a gallmaking herbivore, and on various plant traits that could influence these, were examined. Replicates of four genotypes of Solidago altissima, grown under low, medium, or high levels of nutrient supply in full sun or with medium levels of nutrients in shade, were exposed to mass-released Eurosta solidaginis. The number of plants ovipunctured was significantly affected by plant genotype and the interaction between genotype and nutrient supply to the host plant: one susceptible and one resistant genotype were more preferred, and preference tended to increase with nutrient supply in the more-preferred genotypes. The growth rate of ovipunctured plants during the oviposition period was significantly greater than that of unpunctured plants. Bud diameter (which was strongly correlated with plant growth rate), leaf area, and leaf water content were significant determinants of the percentage of plants ovipunctured, explaining 74% of the variance. The number of surviving larvae was significantly affected by plant genotype, but no effect of nutrient or light supply to the host plant was detected. The ratio of bud diameter to bud length was positively related to the percentage of ovipunctured plants that formed galls, suggesting that the accurate placement of eggs near the apical meristem by ovipositing females may be easier in short, thick buds. No significant correlation was observed between oviposition preference and larval survival at the population level. These results suggest that the plant traits affecting oviposition preference may exhibit different magnitudes of phenotypic plasticity than those affecting larval survival, and that the degree of phenotypic plasticity in plant traits affecting oviposition preference may differ among genotypes within a species.     

Reproductive performance of striped mealybug Ferrisia virgata Cockerell (Hemiptera: Pseudococcidae) on water-stressed cotton plants subjected to nitrogen fertilization

Sap-sucking sessile insects depend on their selected host plant for their development; hence, they are influenced by the nutritional quality of the plant, especially the available nitrogen (N) and water content in the plants. The levels of N in the plant sap can vary as function of the N fertilization applied to enhance crop yield, while deficit of water takes place during drought periods. The performance of the striped mealybug on cotton plants subjected to N fertilization and water stress (=deficit of water) was evaluated. Potted cotton plants grown in a greenhouse were subjected to N fertilization and two irrigation regimes considering regular irrigation and water stress. Cotton plants were infested with 150 newly hatched nymphs. The survival was measured as the percentage of mealybugs alive 25 days after infestation. The biological traits of duration of development + the pre-reproductive period, and the number and sex ratio of the offspring were determined. The survival of nymphs was similar across all treatments and averaged 38 %. Likewise, the developmental times were similar across treatments averaging 47 days, with 84 % of female offspring. However, offspring production was nearly twofold higher for water-stressed plants with successive N fertilizations. Offspring production was increased by 37 % as a function of water stress, and by 18 % as a function of N fertilization. Therefore, we conclude that the striped mealybug performance is enhanced on cotton plants under N fertilization and water stress. Based on the results, proper fertilization and irrigation management relieving plant from stress can be helpful in avoiding generalized infestations of striped mealybug on cotton.     

How do functional traits syndromes covary with growth and reproductive performance in a water‐stressed population of Fagus sylvatica?

A central issue in plant evolutionary ecology is to understand how several coordinated suites of traits (i.e. traits syndrome) may be jointly selected within a single species. This study aims to describe patterns of variation and co‐variation of functional traits in a water‐stressed tree population and test their relationships with performance traits. Within a Mediterranean population of Fagus sylvatica experiencing recurrent summer droughts, we investigated the phenotypic variation of leaf unfolding phenology, leaf area (LA), leaf mass per area (LMA), leaf water content (LWC), water use efficiency (WUE) estimated by carbon isotopic discrimination (d13C), twig Huber‐value (HV: the stem cross‐section divided by the leaf area distal to the stem), wood density (WDens), and leaf nitrogen content (N_mass). First, a principal component analysis revealed that two main axes structured the phenotypic variability: the first axis opposed leaf unfolding earliness and LWC to LMA and WUE; the second axis opposed LA to HV. These two axes can be interpreted as the opposition of two strategies (water economy versus water uptake) at two distinct scales (leaf for the first axis and branches for the second axis). Second, we found that LMA, LA, leaf unfolding and LWC responded differently to competition intensity, while WUE, WDens and HV did not correlate with competition. Third, we found that all studied functional traits were related to growth and/or reproductive performance traits and that these relationships were frequently non‐linear, showing strong interactions between traits. By highlighting phenotypic clustering of functional traits involved in response to water stress and by evidencing antagonistic selection favouring intermediate trait values as well as trait combinations, our study brought new insights on how natural selection operates on plant functional traits in a stressful environment.     

Comparison of life history traits between invasive and native populations of purple loosestrife (Lythrum salicaria) using nonlinear mixed effects model

We compared growth patterns of invasive and native populations of purple loosestrife (Lythrum salicaria) while varying water and nutrient levels. We examined three life-history traits (height, number of branches, and the size of largest leaf) during the growth period adopting a nonlinear mixed effects model. Invasive populations were found to be slower in shoot elongation but grew to be taller than native populations. Invasive populations produced more branches than natives only in the high water, high nutrient treatment. Invasive populations had a similar increase in the size of the largest leaf compared to natives, but ultimately produced a greater size of largest leaf than natives. Invasive populations were found to display a greater vegetative expansion, but this was not strongly affected by our treatments.     

Comparison of life history traits between invasive and native populations of purple loosestrife (Lythrum salicaria) using nonlinear mixed effects model

We compared growth patterns of invasive and native populations of purple loosestrife (Lythrum salicaria) while varying water and nutrient levels. We examined three life-history traits (height, number of branches, and the size of largest leaf) during the growth period adopting a nonlinear mixed effects model. Invasive populations were found to be slower in shoot elongation but grew to be taller than native populations. Invasive populations produced more branches than natives only in the high water, high nutrient treatment. Invasive populations had a similar increase in the size of the largest leaf compared to natives, but ultimately produced a greater size of largest leaf than natives. Invasive populations were found to display a greater vegetative expansion, but this was not strongly affected by our treatments.     

Inheritance of UV-B tolerance in seven ecotypes of Arabidopsis thaliana L. Heynh. and their F1 hybrids

We used a partial diallel mating design to examine morphologic response to supplementary ultraviolet-B (UV-B) radiation of seven ecotypes of Arabidopsis thaliana L. Heynh. from several geographic locations in Europe. We were particularly interested in the inheritance of UV-B tolerance by the F1 generation. Morphologic traits included plant height, rosette diameter, number of shoots (lateral branches from the rosette) and branches (lateral branches above the rosette), and reproductive and vegetative dry mass. To effect a large difference in UV treatments, plants under treatment received 11 kJ/m2/day of biologically effective UV-B radiation while control plants received no UV-B radiation. Genotype effects were observed for all traits (P < .0001), but a significant treatment effect and genotype x treatment interactions were detected only for plant height (P = .0001), rosette diameter (P = .0229), and vegetative (P = .0260) and reproductive dry mass (P = .0900). General combining ability was significant for plant height (P < .0001) and vegetative mass (P = .0563), whereas specific combining ability was significant for rosette diameter (P = .0220) and vegetative mass (P = .0506). These results suggest that both pure lines and hybrids of Arabidopsis can be developed for greater tolerance of UV-B radiation. Similar findings for crop species might lead to the development of UV tolerant varieties.     

Genetic control of growth,biomass allocation,and survival under drought stress in Pinus radiata D. Don seedlings

Drought is one of the critical factors limiting plant growth, and knowledge about genetic adaptation to drought is necessary to develop strategies for successful reforestation on drought-prone sites. In this study, genetic variation was investigated in 98 full- and half-sib radiata pine (Pinus radiata D. Don) families, representing Chilean coastal and interior populations, subjected to two water regimes: well-watered and drought-stressed. Assessed traits, in 5-month-old seedlings, included height (H), diameter (D), height-to-diameter ratio (HDR), dry biomass of needles (NDW), stem (SDW), roots (RDW), and total (TDW), root-to-shoot ratio (RSR), and survival (SUR). After 115 days of treatment, growth, biomass, and survival were nearly two times higher under the well-watered regime than under the stressed one. Families differed significantly in most traits, with individual tree heritabilities ranging from 0.14 for SUR to 0.63 for D in the well-watered treatment. Families from the interior showed the highest heritability for D, SDW, RDW, and TDW when grown in the water-stress treatment. The genetic correlations between treatments were moderately strong, which suggests the presence of a genotype by watering regime interaction. Most traits were strongly correlated (genetic correlations often exceeded 0.40). Compared to the first generation families from coastal sites, the third generation families from the interior sites showed an increase in SUR and RSR. Thus, potential exists to screen families at the seedling stage for drought hardiness and to identify parents from the interior sites with potential to produce a more drought-resistant breed with satisfactory growth rates and yields in dry environments.     

Genotypic Variation in Leaf Water Potential, Stomatal Conductance and Abscisic Acid Concentration in Spring Wheat Subjected to Artificial Drought Stress

A technique for studying variation in the accumulation of abscisicacid (ABA) in response to drought stress is described. Two experiments,each testing 26 spring wheat genotypes, were carried out usingpot grown plants in controlled environment cabinets with nutrientsolution culture, though the results of only one experimentare described in detail. Plants were subjected to water stressby withholding water as the fifth or sixth leaf on the mainstem was emerging. Two stressed plants of each genotype wereharvested 5 and 7 days after the treatment commenced and measurementsof leaf water potential, stomatal conductance and ABA concentrationwere taken. There was considerable genotypic variation in the rate at whichwater potential decreased, partly explained by variation inplant size. Inia 66 (a genotype common to both experiments)had consistently much lower water potentials than the othergenotypes. Stomatal conductances of all genotypes decreasedrapidly and after 5 and 7 days they were negatively correlatedwith the changes in water potential. ABA concentrations varied considerably between genotypes afterboth 5 and 7 days without water, the variation being associatedwith genotypic differences in water potential on these occasions.The overall relationship between ABA concentration and waterpotential was highly significant. Significant differences betweenthe slopes of the regressions for individual genotypes werefound. The cultivar Sirius accumulated the most ABA at any waterpotential and Pelissier, Wascana and Hybrid 46 accumulated theleast. The significance for drought resistance of variation in ABAaccumulation is discussed. Triticum aestivum L. ABA, wheat, absasic acid, leaf water potential, stomatal conductance     

Assessing the importance of genotype x environment interaction for root traits in rice using a mapping population. I: a soil-filled box screen

Altering root system architecture is considered a method of improving crop water and soil nutrient capture. The analysis of quantitative trait loci (QTLs) for root traits has revealed inconsistency in the same population evaluated in different environments. It must be clarified if this is due to genotype × environment interaction or considerations of statistics if the value of QTLs for marker-assisted breeding is to be estimated. A modified split-plot design was used where a main plot corresponded to a separate experiment. The main plot factor had four treatments (environments), which were completely randomized among eight trials, so that each treatment was replicated twice. The sub-plot factor consisted of 168 recombinant inbreed lines of the Bala × Azucena rice mapping population, randomly allocated to the seven soil-filled boxes. The aim of the trial was to quantify QTL × environment interaction. The treatments were chosen to alter partitioning to roots; consisting of a control treatment (high-soil nitrogen, high light and high-water content) and further treatments where light, soil nitrogen or soil water was reduced singly. After 4 weeks growth, maximum root length (MRL), maximum root thickness, root mass below 50 cm, total plant dry mass (%), root mass and shoot length were measured. The treatments affected plant growth as predicted; low nitrogen and drought increased relative root partitioning, low-light decreased it. The parental varieties Bala and Azucena differed significantly for all traits. Broad-sense heritability of most traits was high (57–86%). Variation due to treatment was the most important influence on the variance, while genotype was next. Genotype × environment interaction was detected for all traits except MRL, although the proportion of variation due to this interaction was generally small. It is concluded that genotype × environment interaction is present but less important than genotypic variation. A companion paper presents QTL × environment analysis of data.     

Indirect effects of FRIGIDA: floral trait (co)variances are altered by seasonally variable abiotic factors associated with flowering time

Reproductive timing is a critical life‐history event that could influence the (co)variation of traits developing later in ontogeny by regulating exposure to seasonally variable factors. In a field experiment with Arabidopsis thaliana, we explore whether allelic variation at a flowering‐time gene of major effect (FRIGIDA) affects (co)variation of floral traits by regulating exposure to photoperiod, temperature, and moisture levels. We detect a positive latitudinal cline in floral organ size among plants with putatively functional FRI alleles. Statistically controlling for bolting day removes the cline, suggesting that seasonal abiotic variation affects floral morphology. Both photoperiod and precipitation at bolting correlate positively with the length of petals, stamens, and pistils. Additionally, floral (co)variances differ significantly across FRI backgrounds, such that the sign of some floral‐trait correlations reverses. Subsequent experimental manipulations of photoperiod and water availability demonstrate direct effects of these abiotic factors on floral traits. In sum, these results highlight how the timing of life‐history events can affect the expression of traits developing later in ontogeny, and provide some of the first empirical evidence for the effects of major genes on evolutionary potential.     

Phenotypic plasticity in Philonotis fontana (Bryopsida: Bartramiaceae)

Abstract

Gametophytes from six populations of the moss Philonotis fontana (Hedw.) Brid. were grown under two light and two water regimes in order to assess the effects of these environmental factors on gametophytic architecture and leaf and leaf-cell dimensions. Both light and water affectedgrowth, but the light treatments had a greater effect, and on more characters, than did the water treatments. Significant population effects under common garden conditions point to genetic variation for several traits, and population × environmental treatment interactions demonstratedgenetic variation for patterns of phenotypic plasticity, i.e. plants differed in their 'norms of reaction'. Variation among populations in leaf dimensions tended to have a strong genetic component (20–30% of the total variation), whereas cell dimensions showed relatively little geneticvariation (<10% of the total).     

Physiological and morphological traits associated with adaptation of lucerne (Medicago sativa) to severely drought‐stressed and to irrigated environments

Adaptation to severe drought and to irrigated cropping can both contribute to increased water use efficiency of lucerne, but knowledge on the relevant adaptive traits is limited. Five cultivars featuring contrasting adaptive responses for 3‐year forage yield across 10 agricultural environments of the western Mediterranean basin were currently studied, to identify physiological and morphological traits associated with specific and wide‐adaptation responses. The landraces Mamuntanas, Demnat 203 and Erfoud 1, and the varieties SARDI 10 and Prosementi, were grown in replicated metal containers (55 cm long × 12 cm wide × 75 cm deep; 21 plants per container) under irrigation (weekly restoring soil field capacity) and under moderate and severe drought stress (implying decreased irrigation for 30 days followed by withheld irrigation for 33 and 58 days, respectively). Cultivar post‐stress survival reflected the known cultivar adaptation to drought‐prone agricultural environments. Demnat 203, specifically adapted to irrigated, frequently mown environments, displayed higher amounts of starch, soluble proteins and total nitrogen in the crown and the root under irrigation. This was due to outstanding organ size and, for starch, higher concentrations. Mamuntanas, specifically adapted to drought‐prone environments, exhibited high water‐soluble carbohydrate concentration in storage organs under severe stress, along with a water‐conservation strategy implying less water used in initial drought‐stress phases due to limited early root development that resulted in more water available under severe stress. Drought‐tolerant germplasm also displayed lower wilting under early stress, more plants with green tissues under severe stress, and more stems per plant in stress or favourable conditions. Multivariate patterns of cultivar variation for physiological and morphological traits were strictly associated with cultivar variation for adaptation pattern. Our results highlighted the difficulty to combine some traits of environment‐specific adaptive value into a unique widely adapted variety, supporting the selection of varieties specifically adapted to irrigated or severely drought‐prone environments.     

The phenology of seed‐propagated globe artichoke

The ability of globe artichoke to produce inflorescences (capitula) during the autumn when the market price is highest is lost when plants are propagated from seed, as are most F₁ hybrid cultivars. To gain an understanding of the phenology of seed‐propagated globe artichoke, both vernalised and non‐vernalised seedlings grown from open pollinated progeny of ‘Spinoso sardo’ plants were transplanted into the field at two monthly intervals covering a whole year. Final leaf number and the date of unfolding of each leaf were used to calculate the phyllochrons. The average final leaf number increased from 24 to 88 in response to increasing daylength above an approximately 11 h threshold during the first 30 days after emergence, and this variate explained about 90% of the variation in the thermal time taken to reach the bolting stage. The average phyllochron ranged from 56 to 96°Cd among the six emergence dates and was the major underlying physiological cause of the loss of early flowering shown by seed‐propagated plants. Genotypic variation for phyllochron within an emergence date was strongly associated with variation for the length of the emergence to bolting stage period. The limited effect of vernalisation on development indicated that the late flowering tendency of seed‐propagated plants cannot be attributed to an unfulfilled cold requirement.     

Adaptive value of phenological traits in stressful environments: predictions based on seed production and laboratory natural selection

Phenological traits often show variation within and among natural populations of annual plants. Nevertheless, the adaptive value of post-anthesis traits is seldom tested. In this study, we estimated the adaptive values of pre- and post-anthesis traits in two stressful environments (water stress and interspecific competition), using the selfing annual species Arabidopsis thaliana. By estimating seed production and by performing laboratory natural selection (LNS), we assessed the strength and nature (directional, disruptive and stabilizing) of selection acting on phenological traits in A. thaliana under the two tested stress conditions, each with four intensities. Both the type of stress and its intensity affected the strength and nature of selection, as did genetic constraints among phenological traits. Under water stress, both experimental approaches demonstrated directional selection for a shorter life cycle, although bolting time imposes a genetic constraint on the length of the interval between bolting and anthesis. Under interspecific competition, results from the two experimental approaches showed discrepancies. Estimation of seed production predicted directional selection toward early pre-anthesis traits and long post-anthesis periods. In contrast, the LNS approach suggested neutrality for all phenological traits. This study opens questions on adaptation in complex natural environment where many selective pressures act simultaneously.