Above-ground competition does not alter biomass allocated to roots in Abutilon theophrasti

We tested whether plants allocate proportionately less biomass to roots in response to above-ground competition as predicted by optimal partitioning theory. Two population densities of Abutilon theophrasti were achieved by planting one individual per pot and varying spacing among pots so that plants in the two densities experienced the same soil volume but different degrees of canopy overlap. Density did not affect root:shoot ratio, the partitioning of biomass between fine roots and storage roots, fine root length, or root specific length. Plants growing in high density exhibited typical above-ground responses to neighbours, having higher ratios of stem to leaf biomass and greater leaf specific area than those growing in low density. Total root biomass and shoot biomass were highly correlated. However, storage root biomass was more strongly correlated with shoot biomass than was fine-root biomass. Fine-root length was correlated with above-ground biomass only for the small subcanopy plants in crowded populations. Because leaf surface area increased with biomass, the ratio between absorptive root surface area and transpirational leaf surface area declined with plant size, a relationship that could make larger plants more susceptible to drought. We conclude that A. theophrasti does not reallocate biomass from roots to shoots in response to above-ground competition even though much root biomass is apparently involved in storage and not in resource acquisition.     

Population-level responses to nutrient heterogeneity and density by Abutilon theophrasti (Malvaceae): an experimental neighborhood approach

An experimental approach was used to examine the effects of spatial nutrient heterogeneity and planting density on the sizes of plants within populations of Abutilon theophrasti. Planting locations were generated using random numbers and replicated among populations growing on two different scales of heterogeneity and homogeneous soils. The same quantity of nutrients (dehydrated cow manure) was added to each population, regardless of the spatial nutrient distribution. The higher density was achieved by adding additional planting locations to those present at the lower density. Plant biomass was compared among ten planting locations present in all populations. Plants in seven locations were smaller at the higher density, but the spatial distribution of nutrients affected plant size in only two locations. At the population level, the higher density reduced mean plant biomass and increased both total biomass and the coefficient of variation in biomass, a measure of size inequality. Only when populations on both scales of heterogeneity were together compared with those on homogeneous soils were population-level measurements found to be significantly affected by soil treatment; heterogeneity resulted in decreased total biomass and an increase in the coefficient of variation, apparently due to an increase in the number of small plants in the population. These results, together with the finding that fine root biomass increased in nutrient-enriched patches, suggest that on heterogeneous soils most plants were able to access nutrient patches.     

Altitudinal life history variation in the dung flies Scathophaga stercoraria and Sepsis cynipsea

 Field phenologies of high- (ca. 1500 m) and low- (ca. 500 m) altitude populations of the two most common European species of dung flies, Scathophaga stercoraria and Sepsis cynipsea, differ quite markedly due to differences in climate. To differentiate genetic adaptation due to natural selection and phenotypic plasticity, I compared standard life history characters of pairs of high- and low-altitude populations from three disjunctive sites in Switzerland in a laboratory experiment. The F1 rearing environment did not affect any of the variables of the F2 generation with which all experiments were conducted; hence, there were no carry-over or maternal effects. In Sc. stercoraria, high-altitude individuals were smaller but laid larger eggs; the latter may be advantageous in the more extreme (i.e. more variable and less predictable) high-altitude climate. Higher rearing temperature strongly decreased development time, body size and the size difference between males and females (males are larger), produced female-biased sex ratios and led to suboptimal adult emergence rates. Several of these variables also varied among the three sites, producing some interactions complicating the patterns. In Se. cynipsea, high-altitude females were marginally smaller, less long-lived and laid fewer clutches. Higher rearing temperature strongly decreased development time and body size but tended to increase the size difference between males and females (males are smaller); it also increased clutch size but decreased physiological longevity. Again, interpretation is complicated by variation across sites and some significant interactions. Overall, genetic adaptation to high-altitude conditions appears weak, probably prevented by substantial gene flow, and may be swamped by the effects of other geographic variables among populations. In contrast, phenotypic plasticity is extensive. This may be due to selection of flexible, multi-purpose genotypes. The results suggest that differences in season length between high- and low-altitude locations alone do not explain well the patterns of variation in phenology and body size. Received: 21 March 1996 / Accepted: 1 September 1996     

Morphological canalization,integration, and plasticity in response to population density in Abutilon theophrasti: Influences of soil conditions and growth stages

Phenotypic integration and developmental canalization have been hypothesized to constrain the degree of phenotypic plasticity, but little evidence exists, probably due to the lack of studies on the relationships among the three processes, especially for plants under different environments. We conducted a field experiment by subjecting plants of Abutilon theophrasti to three densities, under infertile and fertile soil conditions, and analyzing correlations among canalization, integration, and plasticity in a variety of measured morphological traits after 50 and 70 days, to investigate the relationships among the three variables in response to density and how these responses vary with soil conditions and growth stages. Results showed trait canalization decreased and phenotypic integration and the degree of plasticity (absolute plasticity) in traits increased with density. Phenotypic integration often positively correlated with absolute plasticity, whereas correlations between trait canalization and plasticity were insignificant in most cases, with a few positive ones between canalization and absolute plasticity at low and medium densities. As plants grew, these correlations intensified in infertile soil and attenuated in fertile soil. Our findings suggested the complexity of the relationship between canalization and plasticity: Decreased canalization is more likely to facilitate active plastic responses under more favorable conditions, whereas increased level of integration should mainly be an outcome of plastic responses. Soil conditions and growth stage may affect responses of these correlations to density via modifying plant size, competition strength, and plastic responses in traits. We also predicted that decreased canalization can be advantageous or disadvantageous, and the lack of response to stress may demonstrate a stronger ability of adaptation than passive response, thus should be adaptive plasticity as active response.     

Evaluation of genetic variation in the daylily (Hemerocallis spp.) using AFLP markers

The daylily (Hemerocallis spp.) is one of the most economically important ornamental plant species in commerce. Interestingly, it is also one of the most heavily bred crops during the past 60 years. Since the American Hemerocallis Society began acting as the official registry of daylily cultivars in 1947, more than 40 000 registrations have been processed. In order to determine the effects of intensive breeding on cultivar development, and to study relationships among different species, genetic variation in the daylily was estimated using AFLP markers. Nineteen primary genotypes (species and early cultivars) and 100 modern cultivars from different time periods were evaluated using 152 unambiguous bands (average 79% polymorphism rate) derived from three AFLP primer combinations. Overall, pairwise similarity estimates between entries ranged between 0.618 and 0.926 (average=0.800). When comparing cultivar groups from different time periods (1940–1998), genetic similarity was initially increased, compared to the primary diploid genotypes, remained constant from 1940 to 1980, and then steadily increased as breeding efforts intensified and hybridizers began focusing on a limited tetraploid germplasm pool derived by colchicine conversion. Among modern (1991–1998) daylily cultivars, genetic similarity has increased by approximately 10% compared to the primary genotypes. These data were also used to evaluate recent taxonomic classifications among daylily species which, with a few minor exceptions, were generally supported by the AFLP data. Received: 15 March 2000 / Accepted: 13 June 2000     

Characteristics of genetic variation in the progenies of protoplast-derived plants of rice, Oryza sativa cv Nipponbare

Genetic variation in protoplast-derived rice (Oryza sativa L.) plants was characterized using first and second generation selfed progenies. A total of 133 regenerated plants were obtained from ten protoplasts of the japonica rice cultivar Nipponbare. Sixty two regenerated plants which set enough seeds for the subsequent field tests at the next generation and were derived from five protoplasts were selected, and their selfed seeds were used as the first selfed-seed progeny generation). Fifteen plants were selected from each of the 15 lines, and their selfed seeds were used for tests at the generation. Thirty seven lines (60%) segregated plants with detrimental mutant characters of yellow-green phenotype, dwarf stature, dense and short panicle, or low seed fertility. According to the segregation patterns in the lines having mutated plants among those originated from the same protoplasts, the stages of mutation induction were estimated. Additionally, five quantitative traits were changed in almost all and lines. Varied quantitative traits of heading date, number of spikelets per panicle, and seed fertility, were in a heterozygous state. However, culm and panicle lengths showed high uniformity, whereas reduced culm and panicle lengths were caused by mutational changes in polygenes and/or multiple genes. Received: 20 March 1996 / Accepted: 21 June 1996     

Reproductive fitness,population size and genetic variation in Muscari tenuiflorum (Hyacinthaceae): The role of temporal variation

In plant populations a positive correlation between population size, genetic variation and fitness components is often found, due to increased pollen limitation or reduced genetic variation and inbreeding depression in smaller populations. However, components of fitness also depend on environmental factors which can vary strongly between years. The dry grassland species Muscari tenuiflorum experiences long term habitat isolation and small population sizes. We analyzed seed production of M. tenuiflorum in four years and its dependence on population size and genetic variation. Genetic diversity within populations was high (AFLP: H_e = 0.245; allozymes: H_e = 0.348). An analysis of molecular variance revealed considerable population differentiation (AFLP: 26%; allozyme: 17%). An overall pattern of isolation by distance was found, which, however was not present at distances below 20 km, indicating stronger effects of genetic drift. Genetic diversity was positively correlated to population size. Self pollination reduced seed set by 24%, indicating inbreeding depression. Reproductive fitness was not correlated to genetic diversity and a positive correlation with population size was present in two of four study years. The absence of a general pattern stresses the importance for multi-year studies. Overall, the results show that despite long term habitat isolation M. tenuiflorum maintains seed production in many years independent of population size. The long term persistence of populations is thus expected to depend less on intrinsic genetic or demographic properties affecting seed production but on successful plant establishment and persistence, which latter are based on conservation and protection of suitable habitats.     

Prediction of genetic gain and gene diversity in seed orchard crops under alternative management strategies

Genetic gain and the gene diversity of seed crops from clonal seed orchards were formulated considering genetic selection, fertility variation and pollen contamination, and compared for five different management strategies. Genetic response was studied as a function of orchard management tactics. Management variables included the proportion of clones left after genetic thinning and/or selective seed harvesting. Formulae were derived to calculate gene diversity (expressed as group coancestry or status number) based on the sex ratio in an orchard population. The influence of having different sets of clones serving as seed parents, or pollen parents, or as both, was analysed. In addition, the impact on genetic gain and the gene diversity of seed crops was studied quantitatively as a function of the quantity and quality of gene flow from outside the orchard. The negative impact of fertility variation among orchard genotypes on the gene diversity of the seed crop was quantified. Numerical examples were given to illustrate the impact of orchard management alternatives on genetic gain and gene diversity. The formulae and results of this study can be used for identifying favourable alternatives for the management of seed orchards. Received: 16 December 2000 / Accepted: 13 March 2001     

Reproductive system and pattern of genetic variation in two Limnanthes species

Summary Several populations of two species of the genus Limnanthes, (L. alba, an outbreeder and L. floccosa, an inbreeder) were examined with respect to variability of fifteen quantitative characters, allozyme variation at 11 loci, and response to different pollination conditions and moisture stress. Nearly equal amounts of phenotypic variability were found in the two species. L. alba had higher within-family variability than L. floccosa, but this result was highly heterogeneous among characters. A study of between- and within-population variance estimates did not reject the null hypothesis that L. alba and L. floccosa are similar with regard to the partitioning and amount of variability for quantitative characters. However, allozyme variation at 11 loci in a large number of populations showed L. alba to be highly polymorphic in contrast to the virtual monomorphism within L. floccosa populations. The average number of alleles per locus in L. alba and L. floccosa was 1.97 and 1.02, respectively, and on an average, L. alba and L. floccosa populations had 63% and 3% loci with polymorphism, respectively. Three groups of allozyme allelic combinations emerged which correlated well with the taxonomic delineation of allogamous L. alba, three semi-autogamous L. floccosa forms and two autogamous L. floccosa forms.All taxa showed a significant reduction in the seed output per plant due to moisture stress. L. alba suffered a further loss of fecundity under the paucity of pollinators, L. floccosa ssp. floccosa showed no significant effect from this factor, whereas L. floccosa ssp. grandiflora exhibited a curvilinear response which peaked at partial pollination and decreased to a lower level at full pollination.The geographic distribution of the two species with regard to the temperature and rainfall distribution did not suggest L. floccosa to be living in drier marginal areas. Patterns of variation in flowering time showed L. alba to be less variable than L. floccosa. Overall, there seemed to be little direct support for the thesis that inbreeding species originated from outcrossing taxa in marginal environments as a direct adaptation to a shortened growing season of xeric environments and to the lack of pollinators. Alternative hypotheses suggest that autogamy in L. floccosa might have evolved as a reproductive isolating barrier acting through either cleistogamy or divergence in flowering times.     

Plasticity of grasshopper vitellogenin production in response to diet is primarily a result of changes in fat body mass

Life history plasticity is the developmental production of different phenotypes by similar genotypes in response to different environments. Plasticity is common in early post-embryonic or adult development. Later in the developmental stage, the transition from developmentally plastic to canalized (i.e., inflexible) phases is often associated with the attainment of a threshold level of storage. Thresholds are often described simply as total body mass or cumulative consumption of food. The physiological characteristics of thresholds, such as the contributions of the growth of particular organs or the production rate of proteins, are largely unstudied. To address the physiology underlying a threshold-induced developmental transition, total vitellogenin production in response to diet quality in the lubber grasshopper was studied. For individuals that differed in age or dietary protein, somatic mass, ovarian mass, fat body mass, mass-specific vitellogenin production, vitellogenin titer, and storage protein titer were measured. Age and diet strongly affected these parameters, with ovarian mass and fat body mass contributing most to the differences. During mid vitellogenesis, females were highly plastic in response to changing food quality. Only during late vitellogenesis were females unresponsive to changes in food quality. Fat body mass was a more important component of plasticity than was mass-specific vitellogenin production. Because these two variables together make up total vitellogenin production, the greater contribution of fat body mass than mass-specific vitellogenin production suggests that growth factors may be more important than tissue stimulators in producing developmental changes in total vitellogenin production. To our knowledge, this is the first study to demonstrate that mass gain of an organ is more important to developmental plasticity than is the output of that same organ.     

Levels of genetic diversity at different stages of the domestication cycle of interior spruce in British Columbia

Concerns over the reductionist nature of the domestication of forest-tree species focus on the possibility of potential genetic erosion during this process. To address these concerns, genetic diversity assessments in a breeding zone the Province of British Columbia “interior” spruce (Picea glauca×engelmanni) program was conducted using allozyme markers. Genetic-variation comparisons were made between natural and production (seed orchard) populations as well as seed and seedling crops produced from the same breeding zone’s seed orchard. The natural population sample consisted of a total of 360 trees representing three stands within each of three watersheds present in the Shuswap-Adams low-elevation zone of interior British Columbia. Small amounts of genetic differentiation were observed among the nine natural populations (4%) and this was attributable to extensive gene flow Consequently, the sum of these nine populations was considered as a baseline for the genetic variation present in the breeding zone. The comparisons between the seed orchard and the breeding zone produced a similar percentage of polymorphic loci while the expected hetrozygosity (0.207 vs 0.210) and the average number of alleles per locus (2.7 vs 2.4) were slightly lower in the seed orchard. A total of seven natural populations’ rare alleles were not present in the orchard population, while one allele was unique to the orchard. The %P increased to 70.6% in the seedlot, but dropped to the natural populations level (64.7%) in the plantation. The observed increase in %P was a result of pollen contamination in the orchard. It is suspected that the reduction in the plantation was caused by an unintentional selection in the nursery. Simulated roguing in the orchard did not drastically reduce even if up to 50% of the orchard’s clones were rogued. However, roguing was associated with a reduction in the average number of alleles per locus (i.e., sampling effect). Received: 2 January 1996 / Accepted: 24 May 1996     

Hierarchical and factorial mating designs for quantitative genetic analysis in tetrasomic potato

Plant breeders need to quantify additive and non-additive components of genetic variance in order to determine appropriate selection methods to improve quantitative characteristics. Hierarchical and factorial mating designs (also known as North Carolina mating designs I and II, respectively) allow one to determine these variance components. The relative advantages of these two designs in the quantitative genetics of tuber yield in tetrasomic potato were investigated. Likewise, the number of female parents to include in design I was also investigated. Data were collected from two independent experiments at two contrasting Peruvian locations: La Molina in the dry coast and San Ramon in the humid mid-altitude. In the first experiment, although design I gave a negative digenic variance (σ² _D), this design provided almost the same estimate of narrow-sense heritability (h²) for tuber yield as that obtained in design II (0.291 and 0.260, respectively). Therefore, design I appears to be appropriate for quantitative genetics research in tetrasomic potato, a crop in which some clones are male sterile. The easy handling of crosses (distinct random females included in the crossing scheme) is another advantage of design I relative to design II. In the second experiment, 12 males were crossed with either two or four females following a design-I mating scheme. The additive genetic variance (σ² _A) was zero (or negative) when two females per male were included but was positive with four females. These results suggest that two females per male may not be enough for design I in tetrasomic potato. Four females per male are preferable to determine σ² _A in design I for this tetrasomic crop. Received: 19 March 2001 / Accepted: 3 July 2001     

Prediction of sample size to maintain genetic variation in doubled-haploid populations following marker selection

Marker selection (MS) and doubled-haploid (DH) technologies have the potential to reduce the time taken to breed new cereal cultivars. However, a limiting factor is the potential increased genetic drift. The aim of this study was to design and test a genetic model for predicting the sample sizes needed to maintain genetic variation among DH plants following marker selection. The model estimates the amount of the genome that is fixed during the production of DH populations of a given size using a given number of markers. To test the model, doubled-haploids were produced from wheat plants selected for three PCR-based markers. When the genetic variation of the DH population (108 plants), produced from 15 selected F₂ plants homozygous at three loci, was compared to the genetic variation of an unselected F₃ population (200 plants), five of the six measured quantitative traits were identical and normally distributed. This model should prove to be a valid breeding tool, allowing a breeder to apply MS to a breeding programme and estimate the minimum DH population sizes required for minimal loss of genetic variation through genetic drift. Received: 16 October 2000 / Accepted: 20 March 2001     

Automated sizing of fluorescent-labeled simple sequence repeat (SSR) markers to assay genetic variation in soybean

 Simple Sequence Repeat (SSR) allele sizing provides a useful tool for genotype identification, pedigree analysis, and for estimating genetic distance between organisms. Soybean [Glycine max (L.) Merr.] cultivars are identified for Plant Variety Protection (PVP) purposes by standard pigmentation and morphological traits. However, many commercial soybeans arise from a limited number of elite lines and are often indistinguishable based on these traits. A system based on SSR markers would provide unique DNA profiles of cultivars. Fluorescent labeling of alleles combined with automated sizing with internal size standards in each gel lane was used as an alternative to standard [³²P] labeling to assess genetic variability in soybean. Allelic frequencies at 20 SSR loci were determined in 35 soybean genotypes that account for greater than 95% of the alleles in North American soybean cultivars based upon pedigree analysis. An average of 10.1 alleles per locus (range: 5–17), with a mean gene diversity of 0.80 (range: 0.50 to 0.87) were observed at the 20 SSR loci. The 20 loci successfully distinguished modern soybean cultivars that are identical for morphological and pigmentation traits, as well as 7 soybean genotypes reported to be indistinguishable using 17 RFLP probes. Pedigrees of 7 cultivars were studied to estimate stability of SSRs in soybean across generations. Of the 7 pedigrees 6 had one locus in the progeny with an allele(s) that was not present in either parent. These new alleles are most likely the result of mutation. The mutation rate of SSR alleles in soybean was similar to that reported in humans. To avoid difficulty associated with mutation, DNA fingerprint data should be determined from the bulk of 30-50 plants of a cultivar. Received: 24 March 1997 / Accepted: 4 April 1997     

匍匐茎草本蛇莓克隆构型对土壤养分的可塑性反应

克隆植物构型的可塑性可使它在养分斑块性分布的环境中,相应地调整对土壤养分的获取对策,因而可能具有重要的生态学意义。在一项田间实验中,匍匐茎草本蛇莓(Duchesnea indica Focke）经历了不同土壤养分水平（高、中、低和对照）处理,以研究土壤养分对蛇莓克隆构型的影响。结果表明：随着土壤养分水平的增加,间隔子的长度和分枝角度均逐渐降低,而分枝强度和分株密度增加。在不同养分水平生镜中,蛇莓克隆构型相关特征的可塑性变化可用动态Logistic模型进行模拟和预测,拟合效果较好。结合植物对环境异质性的利用对策,对所揭示的蛇莓克隆构型可塑性进行了讨论。     

Characterisation of resistance to turnip mosaic virus in oilseed rape (Brassica napus) and genetic mapping of TuRB01

Turnip mosaic virus (TuMV) is the major virus infecting Brassica crops. A dominant gene, TuRB01, that confers extreme resistance to some isolates of TuMV on Brassica napus (oilseed rape), has been mapped genetically. The mapping employed a set of doubled-haploid lines extracted from a population used previously to develop a reference RFLP map of the B. napus genome. The positioning of TuRB01 on linkage group N6 of the B. napus A–genome indicated that the gene probably originated from Brassica rapa. Resistance phenotypes were confirmed by indirect plate-trapped antigen ELISA using a monoclonal antibody raised against TuMV. The specificity of TuRB01 was determined using a wide range of TuMV isolates, including representatives of the European and American/Taiwanese pathotyping systems. Some isolates of TuMV that did not normally infect B. napus plants possessing TuRB01 produced mutant viruses able to overcome the action of the resistance gene. TuRB01 is the first gene for host resistance to TuMV to be mapped in a Brassica crop. A second locus, TuRB02, that appeared to control the degree of susceptibility to the TuMV isolate CHN 1 in a quantitative manner, was identified on the C-genome linkage group N14. The mapping of other complementary genes and the selective combining of such genes, using marker-assisted breeding, will make durable resistance to TuMV a realisable breeding objective. Received: 14 December 1998 / Accepted: 10 April 1999     

Genetic variation in pea (Pisum) dehydrins: sequence elements responsible for length differences between dehydrin alleles and between dehydrin loci in Pisum sativum L.

 The electrophoretic patterns of dehydrins extracted from mature seeds of a range of pea (Pisum) species revealed extensive variation in dehydrin polypeptide mobility. Variation was also observed among lines of P. sativum. Crosses between lines with different dehydrin electrophoretic patterns produced F₁ seeds with additive patterns, and segregation in the F₂ generation was consistent with a 1 : 2 : 1 ratio, indicating allelic variation at each of two dehydrin loci (Dhn2, Dhn3). Genetic linkage was observed between Dhn2 and Dhn3, and the segregation ratios indicated preferential transmission of one allele at the Dhn3 locus. Dehydrin cDNA clones were characterised that encoded the allelic variants at Dhn2 and Dhn3. Their deduced amino-acid sequences were very similar to each other as well as to the product of the Dhn1 locus reported previously. Comparisons were made between the sequences of allelic variants at a single locus, and between the products of different loci. Differences in the electrophoretic mobilities between allelic variants at Dhn2 and Dhn3 were associated with differences in polypeptide length resulting principally from tandem duplications of 21 (Dhn2) or 24 (Dhn3) amino-acid residues. These duplications accounted for much of the difference in length between dehydrins encoded by the different loci. The conserved core of one of the duplicated regions varied in copy number, and small insertions/deletions of amino acids near this core also contributed to length variation both between allelic forms and between loci. Dehydrins possess characteristic highly conserved amino-acid sequence motifs, yet vary considerably in length. Mechanisms involving sequence duplication appear to be responsible for generating the length differences observed between allelic variants as well as between the products of different loci. Received: 12 June 1997 / Accepted: 29 October 1997     

Genetic variation in stomatal and biochemical limitations to photosynthesis in the annual plant, Polygonum arenastrum

 Terrestrial plant photosynthesis may be limited both by stomatal behavior and leaf biochemical capacity. While inferences have been made about the importance of stomatal and biochemical limitations to photosynthesis in a variety of species in a range of environments, genetic variation in these limitations has never been documented in wild plant populations. Genetic variation provides the raw material for adaptive evolution in rates of carbon assimilation. We examined genetic variation in gas exchange physiology and in stomatal and biochemical traits in 16 genetic lines of the annual plant, Polygonum arenastrum. The photosynthesis against leaf internal CO₂ (A−ci) response curve was measured on three greenhouse-grown individuals per line. We measured the photosynthetic rate (A) and stomatal conductance (g), and calculated the internal CO₂ concentration (ci) at ambient CO₂ levels. In addition, the following stomatal and biochemical characteristics were obtained from the A−ci curve on each individual: the degree of stomatal limitation to photosynthesis (L_s), the maximum ribulose 1,5-biphosphate carboxylase-oxygenase (Rubisco) activity (Vc_max) and electron transport capacity (J_max). All physiological traits were genetically variable, with broad sense heritabilities ranging from 0.66 for L_s to 0.94 for J_max. Strong positive genetic correlations were found between Vc_max and J_max, and between g and biochemical capacity. Path analyses revealed strong causal influences of stomatal conductance and leaf biochemistry on A and ci. Path analysis also indicated that L_s confounds both stomatal and biochemical effects, and is an appropriate measure of stomatal influences on photosynthesis, only when biochemical variation is accounted for. In total, our results indicate that differences among lines in photosynthesis and ci result from simultaneous changes in biochemical and stomatal characteristics and are consistent with theoretical predictions that there should be co-limitation of photosynthesis by ribulose-1,5-biphosphate (RuBP) utilization and regeneration, and by stomatal conductance and leaf biochemistry. Gas exchange characteristics of genetic lines in the present study were generally consistent with measurements of the same lines in a previous field study. Our new results indicate that the mechanisms underlying variation in gas exchange include variation in both stomatal conductance and biochemical capacity. In addition, A, g, and ci in the present study tended also to be positively correlated with carbon isotope discrimination (Δ), and negatively correlated with time to flowering, life span, and leaf size based on earlier work. The pattern of correlation between physiology and life span among genetic lines of P. arenastrum parallels interspecific patterns of character correlations. We suggest that the range of trait constellations among lines in P. arenastrum represents a continuum between stress avoidance (rapid development, high gas exchange metabolism) and stress tolerance (slow development, low gas exchange metabolism), and that genetic variation in these character combinations may be maintained by environmental variation in stress levels in the species’ ruderal habitat. Received: 28 March 1996 / Accepted: 13 August 1996     

Microsatellite variability in grapevine cultivars from different European regions and evaluation of assignment testing to assess the geographic origin of cultivars

Nine microsatellite markers (VVMD5, VVMD7, VVS2, ssrVrZAG21, ssrVrZAG47, ssrVrZAG62, ssrVrZAG64, ssrVrZAG79 and ssrVrZAG83) were chosen for the analysis of marker information content, the genetic structure of grapevine cultivar gene pools, and differentiation among grapevines sampled from seven European vine-growing regions (Greece, Croatia, North Italy, Austria and Germany, France, Spain and Portugal). The markers were found to be highly informative in all cultivar groups and therefore constitute a useful set for the genetic characterization of European grapevines. Similar and high levels of genetic variability were detected in all investigated grapevine gene pools. Genetic differentiation among cultivars from different regions was significant, even in the case of adjacent groups such as the Spanish and Portuguese cultivars. No genetic differentiation could be detected between vines with blue and white grapes, indicating that they have undergone the processes of cultivar development jointly. The observed genetic differentiation among vine-growing regions suggested that cultivars could possibly be assigned to their regions of origin according to their genotypes. This might allow one to determine the geographical origin of cultivars with an unknown background. The assignment procedure proved to work for cultivars from the higher differentiated regions, as for example from Austria and Portugal. Received: 10 April 1999 / Accepted: 25 May 1999     

Environmental and genetic variation in T-cell-mediated immune response of fledgling American kestrels

We investigated genetic and environmental components of variance in avian T-cell-mediated immune response (CMI) through a cross-fostering experiment conducted on wild American kestrels (Falco sparverius). CMI was evaluated in vivo by an experimental challenge with phytohaemagglutinin, a T-cell mitogen, injected intradermally in fledglings. Additionally, we assessed two measures of nutritional condition (body mass and circulating plasma proteins) which could influence the variance components of CMI. A two-way nested ANOVA indicated that CMI of fledgling kestrels was explained more by the nest where the bird was reared (33% of the explained variance) than by the nest of origin (12%). Body mass was explained equally by familial and environmental components, while plasma proteins were only related to the rearing environment. CMI of fledglings was not related to their circulating plasma proteins, but was positively correlated with their body mass. Fledgling body mass seemed to be influenced by pre-hatching or post-hatching maternal effects prior to manipulation since resemblance in body mass of sibships at the age of manipulation was high (h ²≤0.58), and body mass at this age predicted body mass at fledging. Therefore, pre-manipulation parental effects on body mass, such as investment in egg size, could have inflated the familial effects on body mass of fledglings and then on its correlated CMI. When controlling for body mass, most of the variation in CMI of fledglings was explained by the nest where the bird was reared (36.6%), while the variance explained by the nest of origin (4%) was not significant. This means that environmental influences are major determinants of offspring CMI. The low proportion of variance explained by the familial component may have been due to the high correlation of CMI to fitness. Received: 19 October 1999 / Accepted: 23 December 1999