Pre‐zygotic parental environment modulates seed longevity

The potential for the pre‐zygotic plant growth environment to play a role in determining seed longevity was investigated for a species that inhabits arid to semi‐arid Australia. Seed longevity is particularly important for wild populations in fluctuating environments because the longer a seed‐lot is able to survive in the soil seed bank the more likely it is to buffer the population from unpredictable environments. Thus Wahlenbergia tumidifructa plants received wet or dry soil moisture within a warm or cool glasshouse until flowering. Seeds subsequently produced by flowers that opened on the day that plants were moved to a common environment were collected at maturity and longevity assessed by controlled ageing at 60% relative humidity and 45°C. Mean seed longevity was similar for seeds produced by plants that grew in warm‐wet, warm‐dry and cool‐dry conditions (P₅₀ of about 20 days), but extended for plants in cool‐wet conditions (P₅₀ = 41.7 days). Cool temperatures resulted in seeds with a wider distribution of lifespans (σ = 20 days) than warm conditions (σ = 12 days); the large σ caused the extended P₅₀ for cool‐wet plants, but not cool‐dry as a result of a concomitant reduction in initial seed germination (K_i). After moving to the common environment, all plants generated new vegetative material, which went on to produce seeds with similar longevity (P₅₀ approx. 20 days) irrespective of original environment. Visible phenotypic responses of the parent to environmental conditions correlated with longevity and quality parameters of the progeny seeds, suggesting that a parental effect modified seed longevity. Our study provides novel empirical data showing that environmental conditions expected under climate change scenarios may potentially cause seed longevity to decline for a species that inhabits arid to semi‐arid Australia. These negative impacts on population buffering may weaken the storage effect mechanism of species coexistence in fluctuating environments.     

Patterns of introduction and adaptation during the invasion of Aegilops triuncialis (Poaceae) into Californian serpentine soils

Multiple introductions can play a prominent role in explaining the success of biological invasions. One often cited mechanism is that multiple introductions of invasive species prevent genetic bottlenecks by parallel introductions of several distinct genotypes that, in turn, provide heritable variation necessary for local adaptation. Here, we show that the invasion of Aegilops triuncialis into California, USA, involved multiple introductions that may have facilitated invasion into serpentine habitats. Using microsatellite markers, we compared the polymorphism and genetic structure of populations of Ae. triuncialis invading serpentine soils in California to that of accessions from its native range. In a glasshouse study, we also compared phenotypic variation in phenological and fitness traits between invasive and native populations grown on loam soil and under serpentine edaphic conditions. Molecular analysis of invasive populations revealed that Californian populations cluster into three independent introductions (i.e. invasive lineages). Our glasshouse common garden experiment found that all Californian populations exhibited higher fitness under serpentine conditions. However, the three invasive lineages appear to represent independent pathways of adaptation to serpentine soil. Our results suggest that the rapid invasion of serpentine habitats in California may have been facilitated by the existence of colonizing Eurasian genotypes pre‐adapted to serpentine soils.     

Effects of Biological Soil Crusts on Seed Bank, Germination and Establishment of Two Annual Plant Species in the Tengger Desert (N China)

The presence of biological soil crusts can affect the germination and survival of vascular plants, but the reasons are not well investigated. We have conducted a field investigation and greenhouse experiments to test the effect of crusts on two desert annual plants, which occur on the stabilized dunes of the Tengger Desert in N China. The results showed that biological soil crusts negatively influenced the seed bank of Eragrostis poaeoides and Bassia dasyphylla. The important effect of biological soil crusts on seed germination and establishment were performed indirectly through reducing the amount of germinating seeds. Field investigation and experimental results with regard to the seed bank indicated that higher seedling density was found in disturbed crust soil and bare soil surface than in intact crust soils. Greenhouse experiments showed that the effects of biological soil crusts on germination and establishment of the two plants are not obvious in moist condition, while disturbed crusts are more favorable to seed germination in dry treatment. Significant differences in biomass were found between disturbed crust soil and bare soil. Survival and growth of the two annual plants were enhanced in both algal and moss crusts during the season of rainfall or in moist environment, but crusts did not affect seedling survival in the dry period. The small seeded E. poaeoides has higher germination than larger-seeded B. dasyphylla in crust soils, but B. dasyphylla has a relatively higher survival rate than E. poaeoides in crust soils.     

Adaptive transgenerational plasticity in the perennial Plantago lanceolata

Phenotypes of plants, and thus their ecology and evolution, can be affected by the environmental conditions experienced by their parents, a phenomenon called parental effects or transgenerational plasticity. However, whether such effects are just passive responses or represent a special type of adaptive plasticity remains controversial because of a lack of solid tests of their adaptive significance. Here, we investigated transgenerational effects of different nutrient environments on the productivity, carbon storage and flowering phenology of the perennial plant Plantago lanceolata, and whether these effects are influenced by seasonal variation in the maternal environment. We found that maternal environments significantly affected the offspring phenotype, and that plants consistently produced more biomass and had greater root carbohydrate storage if grown under the same environmental conditions as experienced by their mothers. The observed transgenerational effects were independent of the season in which seeds had matured. We therefore conclude that transgenerational effects on biomass and carbon storage in P. lanceolata are adaptive regardless of the season of seed maturation.     

THE EVOLUTIONARY GENETICS OF AN ADAPTIVE MATERNAL EFFECT: EGG SIZE PLASTICITY IN A SEED BEETLE

In many organisms, a female's environment provides a reliable indicator of the environmental conditions that her progeny will encounter. In such cases, maternal effects may evolve as mechanisms for transgenerational phenotypic plasticity whereby, in response to a predictive environmental cue, a mother can change the type of eggs that she makes or can program a developmental switch in her offspring, which produces offspring prepared for the environmental conditions predicted by the cue. One potentially common mechanism by which females manipulate the phenotype of their progeny is egg size plasticity, in which females vary egg size in response to environmental cues. We describe an experiment in which we quantify genetic variation in egg size and egg size plasticity in a seed beetle, Stator limbatus, and measure the genetic constraints on the evolution of egg size plasticity, quantified as the genetic correlation between the size of eggs laid across host plants. We found that genetic variation is present within populations for the size of eggs laid on seeds of two host plants (Acacia greggii and Cercidium floridum; h² ranged between 0.217 and 0.908), and that the heritability of egg size differed between populations and hosts (higher on A. greggii than on C. floridum). We also found that the evolution of egg size plasticity (the maternal effect) is in part constrained by a high genetic correlation across host plants (r_G > 0.6). However, the cross-environment genetic correlation is less than 1.0, which indicates that the size of eggs laid on these two hosts can diverge in response to natural selection and that egg size plasticity is thus capable of evolving in response to natural selection.     

Effect of Burkholderia (Pseudomonas) cepacia and soil type on the control of crown rot in wheat

A rifampicin-resistant isolate of Burkholderia (Pseudomonas) cepacia (A3R) reduced crown rot (Fusarium graminearum Group 1) symptoms significantly (P 0.05) in wheat in glasshouse and field experiments and increased grain yield significantly (P 0.05) in one of two field experiments. In glasshouse experiments, applying the bacteria as a soil drench (2.5 × 109 cfu/g soil) was more effective than coating the bacteria on wheat seed (3.4 × 107cfu/seed). In field experiments, the bacteria were applied as a soil drench at the rate of 1.8 x 10¹⁰ cfu/m row. In both the glasshouse and the field, disease severity in the bacteria-inoculated treatments was significantly less in a silt loam than in a sandy loam. The silt loam had a large proportion of fine clay and silt particles (51.7%), which may have favoured the biocontrol activity and survival of the introduced B. cepacia. In a glasshouse experiment, control by B. cepacia was significantly greater in the silt loam than in the sandy loam, which in turn was greater than in a loamy sand. The loamy sand appeared to favour crown rot development but not the activity or survival of the bacterial antagonist. The latter was reflected by the relative populations of the rifampicin-resistant bacteria re-isolated from the various soils during a 5-week period after application of the bacteria (silt loam > sandy loam > loamy sand). This study further confirms that soil type can influence the populations and the level of biocontrol activity of some bacterial antagonists.     

Reproductive challenges of a rare grass,Calamagrostis porteri subsp. insperata (Swallen) C. Greene: implications for habitat restoration

Background: Habitat management for reproductively challenged rare species is a problem when there is insufficient knowledge of their autecology. This study investigated reproductive failure in the rare grass Calamagrostis porteri ssp. insperata (Swallen) C. Greene (Reed bentgrass). Does the management recommendation of high light stimulate clonal growth, flowering, and seed production? Location: Shawnee National Forest, IL, USA, and in a greenhouse and an experimental garden at Southern Illinois University, Carbondale, IL, USA. Methods: Clones obtained from the three known Illinois populations were grown in a glasshouse under experimental light and soil moisture treatments. After 3 years, plants from the high light treatment were planted outside in an experimental garden where the light treatments were maintained for two more years. In the field, vegetative and flowering tiller density, canopy cover, and associated biotic and abiotic variables including abundance of co‐occurring plant species were monitored for 5 years. The overhead tree canopy was cleared over a portion of one population. Results: In the glasshouse, plants increased in size under high light and moist soil, and there were size differences among populations. Sixty‐six per cent (20 of 30) of the genets flowered when planted outdoors under full sunlight but did not produce seed. In the field, flowering only occurred in Calamagrostis growing in the cleared area, but no seed were produced. The plants in the flowering population were smaller than plants in the other two populations. The herbaceous community associated with Calamagrostis in the open diverged from the communities remaining under the shade. Conclusions: This study highlights the difficulty of managing reproductively challenged rare species. Calamagrostis populations can be managed to enhance clonal growth, but establishment of new populations would require translocation of vegetative material as it is highly unlikely that seed can be obtained.     

Distribution of bulbil- and seed-producing plants of Poa alpina (Poaceae) and their growth and reproduction in common gardens suggest adaptation to different elevations

• Premise of the study: The European Alps harbor a spatially heterogeneous environment. Plants can be adapted genetically to this heterogeneity but may also respond to it by phenotypic plasticity. We expected the important fodder grass Poa alpina to be adapted to elevation either genetically or plastically. • Methods: We investigated in three elevational common gardens whether growth and reproductive allocation of plants reproducing either by seeds or bulbils suggest adaptation to their elevation of origin and to what extent they can respond plastically to different elevations. Additionally, we analyzed genetic diversity using microsatellites and tested whether seeds are of sexual origin. • Key results: In the field, bulbil-producing plants occurred more often at higher elevations, whereas seed-producing plants occurred more often at lower elevations, but bulbil-producing plants were generally less vigorous in the common gardens. The response of plants to elevational transplantation was highly plastic, and vigor was always best at the highest location. The small genetic differences were not clinally related to elevation of origin, underlining the importance of phenotypic plasticity. Reproductive allocation was, however, independent of elevational treatments. Seed-producing plants had higher genetic diversity than the bulbil-producing plants even though we found that seed-producing plants were facultative apomicts mostly reproducing asexually. • Conclusions: Bulbil-producing P. alpina, showing a fitness cost at lower elevations compared with seed-producing plants, seem better adapted to higher elevations. By means of its two reproductive modes and the capacity to adjust plastically, P. alpina is able to occupy a broad ecological niche across a large elevational range.     

THE EVOLUTION OF RESISTANCE TO HERBIVORY IN IPOMOEA PURPUREA. II. NATURAL SELECTION BY INSECTS AND COSTS OF RESISTANCE

An important component of the process of coevolution between plants and their insect herbivores is the imposition of selection on plants by insects. Although such selection has been inferred from indirect evidence, little direct evidence for it exists. One goal of this study was to seek direct evidence by determining, for a single plant-herbivore system, whether insect herbivores impose selection on their host plants. A second goal was to determine whether costs are associated with genotypes that confer resistance to herbivores, as has been commonly postulated. The annual morning glory, Ipomoea purpurea, exhibits genetic variation in resistance to four different types of insects. For three of these types, most of the genetic variation is additive. Removal of insect herbivores increased the number of seeds produced by I. purpurea by 20% and eliminated additive genetic variation for seed number (fitness). This result implies that herbivores impose selection on some trait(s) of their host plants. Coupled with selection for decreased damage by corn earworms, as revealed by a negative additive genetic covariance between damage and fitness, this result suggests that insect herbivores impose selection on resistance to corn earworms in I. purpurea. Two types of cost of resistance to herbivores were sought in I. purpurea: 1) internal trade-offs in allocation of resources and 2) ecological trade-offs between resistances to different insects. No costs of either type were detected. This result suggests that cost-benefit arguments that attempt to predict the evolution of levels of resistance to herbivores are not applicable to I. purpurea.     

Effects of saline‐waterlogging and dryness/moist alternations on seed germination of halophyte and xerophyte

In arid zones, precipitation distribution is extremely uneven, with saline‐waterlogging and dry–moist cycles appearing frequently, which negatively impact on seed germination and seedling establishment. The responses of two halophytes, Suaeda physophora and Haloxylon ammodendron, and a xerophyte, Haloxylon persicum, to saline‐waterlogging and dry–moist cycles were studied. The results showed that aeration increased seed germination for all species when seeds were submerged in NaCl, especially for xerophyte. Compared with S. physophora and H. ammodendron, seed germination, recovery germination, and total germination of H. persicum were much lower when seeds were submerged in 700 mm NaCl, especially for the recovery germination and total germination of nongerminated seeds when the seeds were desiccated and then transferred to distilled water. However, when the seeds were submerged in 700 mm NaCl with aeration, the seed germination, recovery germination, and total germination of nongerminated seeds transferred to distilled water increased dramatically for H. persicum. No adverse effect of desiccation was found on those values of nongerminated seeds pretreated in NaCl with or without aeration for the two halophytes. In conclusion, seeds of the two halophytes were more tolerant to waterlogging and dry–moist cycles than seeds of the xerophyte during emergence under saline conditions; these traits may be important for halophytes to survive extreme saline environments during the seed germination stage.     

An AGAMOUS intron‐driven cytotoxin leads to flowerless tobacco and produces no detrimental effects on vegetative growth of either tobacco or poplar

Flowerless trait is highly desirable for poplar because it can prevent pollen‐ and seed‐mediated transgene flow. We have isolated the second intron of PTAG2, an AGAMOUS (AG) orthologue from Populus trichocarpa. By fusing this intron sequence to a minimal 35S promoter sequence, we created two artificial promoters, fPTAG2I (forward orientation of the PTAG2 intron sequence) and rPTAG2I (reverse orientation of the PTAG2 intron sequence). In tobacco, expression of the β‐glucuronidase gene (uidA) demonstrates that the fPTAG2I promoter is non‐floral‐specific, while the rPTAG2I promoter is active in floral buds but with no detectable vegetative activity. Under glasshouse conditions, transgenic tobacco plants expressing the Diphtheria toxin A (DT‐A) gene driven by the rPTAG2I promoter produced three floral ablation phenotypes: flowerless, neuter (stamenless and carpel‐less) and carpel‐less. Further, the vegetative growth of these transgenic lines was similar to that of the wild‐type plants. In field trials during 2014 and 2015, the flowerless transgenic tobacco stably maintained its flowerless phenotype, and also produced more shoot and root biomass when compared to wild‐type plants. In poplar, the rPTAG2I::GUS gene exhibited no detectable activity in vegetative organs. Under field conditions over two growing seasons (2014 to the end of 2015), vegetative growth of the rPTAG2I::DT‐A transgenic poplar plants was similar to that of the wild‐type plants. Our results demonstrate that the rPTAG2I artificial promoter has no detectable activities in vegetative tissues and organs, and the rPTAG2I::DT‐A gene may be useful for producing flowerless poplar that retains normal vegetative growth.     

Comparative responses of Achillea millefolium ecotypes to competition and soil type

Summary Achillea millefolium populations from adjacent sites with zonal and serpentime soil were used to test predictions about the relation between growth and the competitive ability of plants in productive and unproductive environments. Under greenhouse conditions, individually-grown plants from both sources grew larger in serpentine soil than in zonal soil; serpentine plants accumulated 72% more biomass than zonal plants. In zonal soil, zonal plants were 71% larger than serpentine plants, although these differences were not statistically significant, and plants from both sources accumulated much less biomass and were shorter than plants growing in serpentine soil. In a high density, fertilized replacement series, zonal plants were taller and heavier but exhibited no more competitive ability than serpentine plants. The predictions that rapid height growth and biomass accumulation contribute significantly to competitive ability are not supported by our results. Although ecotypic differentiation has occurred between these A. millefolium populations, apparently in response to different soil types, the expression of these heritable differences can be masked by other environmental effects. There has been no apparent trade-off in these ecotypes between their response to the physical environment and their competitive ability.     

Importance of seed Zn content for wheat growth on Zn-deficient soil

Seed nutrient reserves may be important for an early establishment of crops on low-fertility soils. This glasshouse pot study evaluated effects of seed Zn content on vegetative growth of two wheat (Triticum aestivum L.) genotypes differing in Zn efficiency. Low-Zn (around 250 ng Zn per seed) and high-Zn seed (around 700 ng Zn per seed on average) of Excalibur (Zn efficient) and Gatcher (Zn inefficient) wheats were sown in a Zn-deficient siliceous sand fertilised with 0, 0.05, 0.2, 0.8 or 3.2 mg Zn kg^-1 soil. After 3 weeks, plants derived from the high-Zn seed had better root and shoot growth; the cv. Excalibur accumulated more shoot dry matter than the cv. Gatcher. After 6 weeks, greater root and shoot growth of plants grown from the high-Zn seed compared to those from the low-Zn seed was obvious only at nil Zn fertilisation. A fertilisation rate of 0.2 mg Zn kg^-1 soil was required for achieving 90% of the maximum yield for plants grown from the high-Zn seed compared to 0.8 mg Zn kg^-1 soil for plants derived from the low Zn seed. The critical Zn level in youngest expanded leaves for 90% maximum yield was 16 mg Zn kg^-1 dry matter for both genotypes. Zn-efficient Excalibur had greater net Zn uptake rates compared to Zn-inefficient Gatcher after 3 weeks but they were not different at the 6-week harvest. Zinc-deficient plants had greater net uptake rates of Cu, Mn, B, P, and K but a reduced uptake rate of Fe. It is concluded that higher seed Zn content acted similar to a starter-fertiliser effect by improving vegetative growth and dissipating differences in Zn efficiency of wheat genotypes.     

Serpentine and non-serpentine Silene dioica plants do not differ in nickel tolerance

Serpentine soils are hostile to plant life. They are dry, contain high concentrations of nickel and have an unfavorable calcium/magnesium ratio. The dioecious plant Silene dioica (L.) Clairv. (Caryophyllaceae) is the most common herb on serpentine soils in the Swedish mountains. It also commonly grows on non-serpentine soils in the subalpine and coastal area. I have compared the germination frequency, plant establishment and growth of serpentine and subalpine non-serpentine populations in serpentine soil under greenhouse conditions. Further more I have studied the specific effect of nickel on root and shoot growth of serpentine and non-serpentine plants from the subalpine and coastal area in solutions with different concentrations of nickel. Plants from serpentine and non-serpentine populations grew well and in a similar fashion in serpentine soil. Moreover, S. dioica plants, irrespective of original habitat, tolerated enhanced concentrations of nickel when grown in solutions. An analysis of metal content in serpentine plants from natural populations shows that S. dioica has a higher nickel concentration in the roots than in the shoots. The growth studies show that S. dioica is constitutively adapted to serpentine, and that all populations have the genetic and ecological tolerance to grow on serpentine.     

Further studies on seed transmission of broad bean stain virus and Echtes Ackerbohnenmosaik -Virus in field beans (Vicia faba)

Broad bean stain virus (BBSV) and Echtes Ackerbohnenmosaik-Virus (EAMV) were detected in the seed coat and embryo sac fluid of immature seeds from infected field beans (Viciafaba minor) by inoculation to Phaseolus vulgaris; BBSV was also detected in immature embryos. The proportion of seeds infected with either virus decreased during maturation. The viruses were transmitted to seedlings as often through fully ripened seeds from which the seed coats had been removed as through intact seeds. Both viruses were detected in pollen from infected plants, but in glasshouse tests only BBSV was transmitted through pollen to seeds. Delaying fertilization in plants infected with BBSV or EAMV seemed not to affect seed transmission of either virus. In glasshouse tests BBSV was transmitted more often through seeds from plants that were inoculated before flowering than during flowering, and was not transmitted through seeds from plants inoculated after flowering; EAMV was transmitted only through seeds from plants inoculated before flowering. In tests on seed from naturally infected plants BBSV was transmitted more often through seeds from plants that developed symptoms before flowering than during flowering. Both viruses were seed-borne in all cultivars tested and there was no marked difference in the frequency of transmission of either virus among the spring-sown cultivars most common in Britain. Both viruses persisted in seed for more than 4 yr.     

Fungicide seed treatments increase growth of perennial ryegrass

Field, laboratory and glasshouse experiments were carried out to measure effects of seed treatments with captan or thiram on growth of perennial ryegrass (Lolium perenne L.). Field-sown captan- or thiram-treated seed gave twice as many seedlings as untreated seed. Spaced plants growing from fungicide-treated seed produced almost 6 times more dry matter 16 weeks after sowing than those from untreated seed. This effect, though diminishing with time, was still apparent more than a year after sowing. Fungicides in sterile agar growth medium were phytotoxic to seedlings at concentrations of 10μg/ml and greater. Seedlings grown from treated seeds sown from 5 to 15 mm away from developing colonies of the virulent seedling pathogenFusarium oxysporum Schlecht. were more than 4 times larger than those grown from untreated seeds. Captan-treated seed sown into pots containing field soil produced more and larger seedlings than untreated seed. Methyl bromide fumigation of the same soil also increased both number and size of seedlings. Fungicidal, rather than direct chemical effects, at early stages of seedling growth, account for increased growth of plants from fungicide-treated seed.     

Transgenerational plasticity in Silene vulgaris in response to three types of stress

• The environment experienced by plants can influence the phenotype of their offspring. Such transgenerational plasticity can be adaptive when it results in higher fitness of the offspring under conditions correlated with those experienced by the mother plant. However, it has rarely been tested if such anticipatory parental effects may be induced with different environments.
• We grew clonal replicates of Silene vulgaris under control conditions and three types of stress (nutrient deficiency, copper addition and drought), which are known from natural populations of the species. We then subjected offspring from differently treated mother plants to each of the different stress treatments to analyse the influence of maternal and offspring environment on performance and several functional traits.
• Current stress treatments strongly influenced biomass and functional traits of the plants, mostly in line with responses predicted by the theory of functional equilibrium. Plant performance was also influenced by maternal stress treatments, and some effects independent of initial size differences remained until harvest. In particular, stressed mothers produced offspring of higher fitness than control plants. However, there was no evidence for treatment‐specific adaptive transgenerational plasticity, as offspring from a mother plant that had grown in a specific environment did not grow better in that environment than other plants.
• Our results indicate that the maternal environment may affect offspring traits and performance, but also that this transgenerational plasticity is not necessarily adaptive.

     

Evidence for rapid evolution in a grassland biodiversity experiment

In long‐term grassland experiments, positive biodiversity effects on plant productivity commonly increase with time. Subsequent glasshouse experiments showed that these strengthened positive biodiversity effects persist not only in the local environment but also when plants are transferred into a common environment. Thus, we hypothesized that community diversity had acted as a selective agent, resulting in the emergence of plant monoculture and mixture types with differing genetic composition. To test our hypothesis, we grew offspring from plants that were grown for eleven years in monoculture or mixture environments in a biodiversity experiment (Jena Experiment) under controlled glasshouse conditions in monocultures or two‐species mixtures. We used epiGBS, a genotyping‐by‐sequencing approach combined with bisulphite conversion, to provide integrative genetic and epigenetic (i.e., DNA methylation) data. We observed significant divergence in genetic and DNA methylation data according to selection history in three out of five perennial grassland species, namely Galium mollugo, Prunella vulgaris and Veronica chamaedrys, with DNA methylation differences mostly reflecting the genetic differences. In addition, current diversity levels in the glasshouse had weak effects on epigenetic variation. However, given the limited genome coverage of the reference‐free bisulphite method epiGBS, it remains unclear how much of the differences in DNA methylation was independent of underlying genetic differences. Our results thus suggest that selection of genetic variants, and possibly epigenetic variants, caused the rapid emergence of monoculture and mixture types within plant species in the Jena Experiment.     

EFFECTS OF MATERNAL AND PATERNAL ENVIRONMENT AND GENOTYPE ON OFFSPRING PHENOTYPE IN SOLIDAGO ALTISSIMA L.

To predict the possible evolutionary response of a plant species to a new environment, it is necessary to separate genetic from environmental sources of phenotypic variation. In a case study of the invader Solidago altissima, the influences of several kinds of parental effects and of direct inheritance and environment on offspring phenotype were separated. Fifteen genotypes were crossed in three 5 × 5 diallels excluding selfs. Clonal replicates of the parental genotypes were grown in two environments such that each diallel could be made with maternal/paternal plants from sand/sand, sand/soil, soil/sand, and soil/soil. In a first experiment (1989) offspring were raised in the experimental garden and in a second experiment (1990) in the glasshouse. Parent plants growing in sand invested less biomass in inflorescences but produced larger seeds than parent plants growing in soil. In the garden experiment, phenotypic variation among offspring was greatly influenced by environmental heterogeneity. Direct genetic variation (within diallels) was found only for leaf characters and total leaf mass. Germination probability and early seedling mass were significantly affected by phenotypic differences among maternal plants because of genotype ( genetic maternal effects ) and soil environment ( general environmental maternal effects ). Seeds from maternal plants in sand germinated better and produced bigger seedlings than seeds from maternal plants in soil. They also grew taller with time, probably because competition accentuated the initial differences. Height growth and stem mass at harvest (an integrated account of individual growth history) of offspring varied significantly among crosses within parental combinations ( specific environmental maternal effects ). In the glasshouse experiment, the influence of environmental heterogeneity and competition could be kept low. Except for early characters, the influence of direct genetic variation was large but again leaf characters (= basic module morphology) seemed to be under stricter genetic control than did size characters. Genetic maternal effects, general environmental maternal effects, and specific environmental maternal effects dominated in early characters. The maternal effects were exerted both via seed mass and directly on characters of young offspring. Persistent effects of the general paternal environment ( general environmental paternal effects ) were found for leaf length and stem and leaf mass at harvest. They were opposite in direction to the general environmental maternal effects, that is the same genotypes produced “better mothers” in sand but “better fathers” in soil. The general environmental paternal effects must have been due to differences in pollen quality, resulting from pollen selection within the male parent or leading to pre- or postzygotic selection within the female parent. The ranking of crosses according to mean offspring phenotypes was different in the two experiments, suggesting strong interaction of the observed effects with the environment. The correlation structure among characters changed less between experiments than did the pattern of variation of single characters, but under the competitive conditions in the garden plant height seemed to be more directly related to fitness than in the glasshouse. Reduced competition could also explain why maternal effects were less persistent in the glasshouse than in the garden experiment. Evolution via selection of maternal effects would be possible in the study population because these effects are in part due to genetic differences among parents.     

Development and practice of a glasshouse screening technique for resistance of wheat to the aphid Sitobion avenae

Differences in resistance to S. avenae were confirmed amongst eight spring wheat stocks in glasshouse tests. Taking these stocks as standards, a glasshouse screening technique was developed in which 15 plants of each entry were arranged randomly in one block and aphids were scattered over the whole at the stem-extension phase. When the infestation of individual plants was scored about 2 wk later, resistant and susceptible stocks were well differentiated. Provided that scoring was completed before or at ear emergence, separation of resistant entries was more efficient with older plants. Ranking of the standard stocks was little influenced by other variations of technique or environment. Twenty-six out of 91 previously untested spring wheat breeding lines appeared to be moderately resistant to S. avenae, suggesting that progress in the selection of resistant cultivars will depend more on the further development of suitable techniques than on the availability of heritable resistance.