Generations Of Selfing Research Articles

Genetics of self-compatibility in a self-incompatible wild diploid potato species Solanum chacoense. 1. Detection of an S locus inhibitor (Sli) gene

A self-compatible (SC) variant of a wild diploid potato species, Solanum chacoense, which is normally self-incompatible (SI), was investigated for the nature and genetics of self-compatibility. It was crossed with a SI cultivated diploid potato species, S. phureja. The F1 progeny segregated SC vs. SI. Diallel crosses were made among 15 F1's. Self-compatibility was tested in a selfed family of a parental SC variant and in sib-mated and selfed families of F1 progeny. All the data suggest that there is a single dominant gene (Sli) with sporophytic action inhibiting S gene expression in the pollen. Plants having a ‘Sli’ gene, produce pollen which is compatible to its own parent and plants with similar S genes. The ‘Sli’ gene has been maintained in a heterozygous condition through eight selfing generations (S8) implying that dominant homozygotes might be associated with lethality.

THE EFFECTS OF FIVE GENERATIONS OF ENFORCED SELFING ON POTENTIAL MALE AND FEMALE FUNCTION IN MIMULUS GUTTATUS.

In prior work we detected no significant inbreeding depression for pollen and ovule production in the highly selfing Mimulus micranthus, but both characters showed high inbreeding depression in the mixed-mating M. guttatus. The goal of this study was to determine if the genetic load for these traits in M. guttatus could be purged in a program of enforced selfing. These characters should have been under much stronger selection in our artificial breeding program than previously reported characters such as biomass and total flower production because, for example, plants unable to produce viable pollen could not contribute to future generations. Purging of genetic load was investigated at the level of both the population and the individual maternal line within two populations of M. guttatus. Mean ovule number, pollen number, and pollen viability declined significantly as plants became more inbred. The mean performance of outcross progeny generated from crosses between pairs of maternal inbred lines always exceeded that of self progeny and was fairly constant for each trait through all five generations. The consistent performance of outcross progeny and the universally negative relationships between performance and degree of inbreeding are interpreted as evidence for the weakness of selection relative to the quick fixation of deleterious alleles due to drift during the inbreeding process. The selective removal (purging) of deleterious alleles from our population would have been revealed by an increase in performance of outcross progeny or an attenuation of the effects of increasing homozygosity. The relationships between the mean of each of these traits and the expected inbreeding coefficient were linear, but one population displayed a significant negative curvilinear relationship between the log of male fertility (a function of pollen number and viability) and the inbreeding coefficient. The generally linear form of the responses to inbreeding were taken as evidence consistent with an additive model of gene action, but the negative curvilinear relationship between male fertility and the inbreeding coefficient suggested reinforcing epistasis. Within both populations there was significant genetic variation among maternal lineages for the response to inbreeding in all traits. Although all inbred lineages declined at least somewhat in performance, several maternal lines maintained levels of performance just below outcross means even after four or five generations of selfing. We suggest that selection among maternal lines will have a greater effect than selecting within lines in lowering the genetic load of populations.

Architecture of habitat: design for life

The construction industry and the industries which supply it have a vital role to play in the evolution of a culture of clean technology. Buildings have a crucial impact on the physical and economic health and well–being of the individuals, communities and organizations which they are intended to support. The global impact of the built environment is increasingly evident. It is necessary for everyone involved to recognize the role of buildings in the quality of our lives and the extent of our responsibilities in creating a sustainable habitat. Buildings and their components are basic needs which should be socially responsible products able to contribute to our physical, psychological, cultural and economic well–being; yet they frequently contribute to ill health and alienation, undermine community and create significant financial liability. Modern planning, construction activity, building management and demolition processes are innately unclean and environmentally exploitative. We need to identify the consequences of our actions and to process these to show how we might create a healthy built environment within the ecological limits to which we must all defer. The existing culture of control of the environment must give way to a culture of appreciation and participation. This paper will investigate ecological principles to identify mitigation strategies and the cultural shift which is required to create the intergenerational buildings upon which our future development depends. A critical appraisal of the new generation of self–declared, environmentally benign buildings could assist in determining appropriate directions for evolution of the built environment.

Breeding wheat and rye for resistance to Fusarium diseases

Abstract Fusarium culmorum and F. graminearum Groups 1 and 2 cause seedling blight, crown rot, foot rot and head blight in wheat and rye that may affect grain yield and quality for baking and feeding. This review starts with an analysis of Fusarium populations with regard to their genetic variation for aggressiveness, mycotoxin production, and isolate‐by‐host genotype interaction. To assess resistance in the different host growth stages, quantitative inoculation and disease assessment techniques are necessary. Based on estimated population parameters, breeding strategies are reviewed to improve Fusarium resistance in wheat and rye. Epidemiological and toxicological aspects of Fusarium resistance that are important for resistance breeding are discussed. F. culmorum and F. graminearum display large genetic variation for aggressiveness in isolate collections and in naturally occurring populations. The production of mycotoxins, especially deoxynivalenol and its derivatives, is a common trait in these populations. Significant isolate‐by‐host genotype interactions were not found across environments in wheat and rye.Artificial infections in the field are indispensable for improving Fusarium crown rot, foot rot and head blight resistance in wheat and rye. For a reliable disease assessment of large populations, disease severity ratings were found to be the most convenient. The differentiation of host resistance is greatly influenced by an array of nongenetic factors (macro‐environment, microclimate, host growth stage, host organ) that show significant interactions with host genotype. Selection for environmentally stable resistance has to be performed in several environments under a maximum array of different infection levels. Selection in early growth stages or on one plant organ does not in most cases allow prediction of resistance in adult‐plant stages or another plant organ.Significant genetic variation for resistance exists for all Fusarium‐incited diseases in breeding populations of wheat and rye. The patho‐systems studied displayed a prevalence of additive gene action with no consistent specific combining ability effects and thus rapid progress can be expected from recurrent selection. In wheat, intensive testing of parental genotypes allows good prediction of the mean head blight resistance after crossing. Subsequent selection during selfing generations enables the use of transgression towards resistance. In hybrid breeding of winter rye, the close correlation between foot rot resistance of inbred lines and their GCA effects implies that selection based on the lines per se should be highly effective. This is not valid for F. culmorum head blight of winter rye caused by a greater susceptibility of the inbred lines compared to their crosses.For both foot rot and head blight resistance, a high correlation between the resistance to F. graminearum and F. culmorum was found in wheat and rye. Mycotoxin accumulation occurs to a great extent in naturally and artificially infected plant stands. The correlation between resistance traits and mycotoxin contents are medium and highly dependent on the environment. Further experiments are needed to clarify whether greater resistance will lead to a correlated reduction of the mycotoxin content of the grains under natural infection.

Predicting the range of inbreeding depression of inbred lines in cross-pollinated populations

The objectives of this paper were to derive the genetic variance of inbreeding depression (<img SRC="Image482.gif" WIDTH="48" HEIGHT="33"> ) and to predict the range of inbreeding depression (RID) in cross-pollinated populations. The variance of inbreeding depression is a function of the genetic variances related to dominance effects (<img SRC="Image483.gif" WIDTH="31" HEIGHT="33">, D2, and <img SRC="Image484.gif" WIDTH="21" HEIGHT="25">), and of the inbreeding coefficients of the two generations in which inbreeding depression is measured (Ft and Fg). The results showed that the higher the level of dominance of a trait, the higher the variance of inbreeding depression. The magnitudes of <img SRC="Image485.gif" WIDTH="48" HEIGHT="33">were expected to be lower in improved (mean gene frequencies = <img SRC="Image486.gif" WIDTH="16" HEIGHT="25">> 0.6) and in unimproved (<img SRC="Image487.gif" WIDTH="16" HEIGHT="25"> < 0.4) populations, than in composite populations (<img SRC="Image487.gif" WIDTH="16" HEIGHT="25"> <FONT FACE="Symbol">»</font> 0.5). Data from a maize population used to illustrate the study showed that the range of inbreeding depression in the S<FONT FACE="Symbol">¥</font> generation of selfing was from 48.7% to 85.3% for grain yield, and from 13.9% to 24.5% for plant height. A mating design outlined to estimate the genetic variance of inbreeding depression, the range of inbreeding depression, and of the range of inbred lines is presented.

FIVE GENERATIONS OF ENFORCED SELFING AND OUTCROSSING IN MIMULUS GUTTATUS: INBREEDING DEPRESSION VARIATION AT THE POPULATION AND FAMILY LEVEL.

The focus of this study was to examine the consequences of five sequential generations of enforced selfing and outcrossing in two annual populations of the mixed-mating Mimulus guttatus. Our primary goal was to determine whether purging of deleterious recessive alleles occurs uniformly between populations and among families, and thus gain insights into the mode of gene action (dominance, overdominance, and/or epistasis) governing the expression of inbreeding depression at both the population and family levels across the life cycle.

Transfer of powdery mildew resistance from Aegilops variabilis into bread wheat

Winter hexaploid wheat (Triticum aestivum L.) was crossed with Aegilops variabilis to transfer resistance to powdery mildew into wheat. Following two backcrosses to wheat and from 5 to 9 generations of selfing, several disomic addition and substitution lines of hexaploid wheat resistant to the mildew pathogen were isolated. A pair of short satellited chromosomes was always observed in the resistant lines. Further evidence utilizing as markers for homoeologous group 1 HMW glutenin subunits and DNA hybridization with probe pGBX 3076 showed that an alien substitution involved this homoeologous group.

Self-compatibility and heterosis in white clover (Trifolium repens L.)

Inbred lines of white clover (Trifolium repens L.) have been produced utilising the rare self-fertility (Sf) allele. Twenty-two lines of four distinct groups have been maintained through five generations of selfing by single seed descent. Fourteen lines were used in crosses to produce F1s. Both parents and hybrids were analysed for a range of morphological characters. Positive heterosis for dry matter production was observed in half the hybrids. No other trait showed significant heterosis. The degree of heterosis appears to be related to the extent of variation in morphological characters between the parental lines, some combinations of lines yielding heterotic hybrids in all cases, others in none. The majority of the F1 hybrids are superior in terms of dry matter production to eight control varieties.

Somatic excision of the Ac transposable element in transgenic Arabidopsis thaliana after 5-azacytidine treatment.

We have introduced the maize Ac transposable element in Arabidopsis thaliana and found that after three selfing generations, the element is immobile and extensively methylated. Moreover, the nopaline synthase (nos) gene present on the same transferred T-DNA, was active early after transformation and regeneration, but inactive in most of the S1 progeny. We used 5-azacytidine (5AzaC) to determine whether a reduction in the methylation would affect both Ac transposition and expression of the nos gene. After treatment with 5AzaC doses from 0.3 mM to 1.0 mM, approximately 25% of the plants produced detectable amounts of nopaline, indicating that the nos gene was reactivated. Using the polymerase chain reaction (PCR) to detect the empty donor site left by Ac transposition, we demonstrated that 5AzaC also activates Ac excision in the transgenic plants. Approximately 13% of the 5AzaC treated plants (doses from 0.1 mM to 1.0 mM) were shown to have empty donor sites due to Ac excision. None of the plants cultivated in the absence of 5AzaC showed evidence for Ac transposition or reactivation of the nos gene. Further analysis using Southern blot indicate that some demethylation occurred in the genome of individual plants. These results may represent demethylation in few cells during development which may be sufficient to reactivate in these cells the expression of the nos and Ac transposase transgenes, the latter promoting Ac transposition in somatic cells.

Postharvest Longevity of Antirrhinum majus L. Cut Flowers as Influenced by Backcrosses to a Short-lived Recurrent Parent and Harvest Time

An inbred backcrossing approach was taken to transfer long postharvest keeping time of cut flowers from a white inbred line of Antirrhinum majus L. into a yellow short-lived inbred line. Three backcrosses to the short-lived recurrent parent were done followed by three generations of selfing by single-seed descent. Plants from 56 accessions of BC1S3 through BC3S3 were grown twice (June and August 1995) in a greenhouse and flower stems harvested for postharvest longevity evaluation. Postharvest evaluation was done in deionized water under continuous fluorescent light. Longevity was determined as the number of days from cutting to discard when 50% of the open florets on a flower stem wilted or turned brown. One yellow accession was retrieved that was not significantly different in postharvest longevity from the white long-lived parent. Environment substantially influenced postharvest longevity over harvest dates. Possible causes for variation of postharvest keeping time will be presented.

Testcross Selection Prior to Further Inbreeding in Maize: Mean Performance and Realized Genetic Variance

Testcross evaluation of maize (Zea mays L.) families is usually done after, but not prior to, several generations of selfing. The objectives of this study were to (i) evaluate the usefulness of one cycle of testcross selection and recombination of F3 families prior to further selfing and (ii) develop a method for estimating realized genetic variance. In each of two biparental maize populations (POP1 and POP2), five Cycle F3 families that had the highest yields when testcrossed to B73 were recombined to form Cycle 1. Testcrosses of Cycle 1, Cycle 0, and the five selected Cycle 0 F3 families were evaluated at five locations in 1993. Selection differentials (S) for yield were 7 to 8% of the corresponding Cycle 0 means. Observed response to selection (R) expressed as a proportion of the Cycle 0 mean was 7% in POP1 and 5% in POP2. In each population, the five highest‐yielding Cycle 1 testcrosses outyielded the five highest‐yielding Cycle 0 testcrosses by 8 to 9%. Testcross selection would have added 2 yr to the time required for inbred development, but average gains per year for yield were 0.9% larger with than without selection and recombination of the best five F3 families in Cycle 0. Realized genetic variance was estimated as Rσ̂2G = SR/i2, where i was the standardized selection differential with truncation selection. There was no evidence that genetic variance decreased after one cycle of testcross selection. In experiments that compare several cycles of selection, realized genetic variance can be estimated with bulks of all families and bulks of the selected families instead of estimating genetic variance with large numbers of individual families in each cycle.

Production and Characterization of Tobacco Addition Lines Carrying Nicotiana debneyi Chromosomes with a Gene for Resistance to Black Root Rot

Black root rot, caused by Chalara elegans Nag. Raj and Kendrick (syn: Thielaviopsis basicola [Berk. and Broome] Ferr.), is a common soil‐borne fungal disease in cultivated tobacco (Nicotiana tabacum L., 2n = SSTT=48). Only polygenic partial resistance to this disease is available in the original tobacco genomes; however, Nicotiana debneyi Domin, a tetraploid relative of tobacco (2n = XXYY = 48) has complete resistance to a wide spectrum of black root rot biotypes. A fertile somatic hybrid between N. tabacum ‘Delgold’ and N. debneyi was previously produced and was used to transfer the N. debneyi black root rot resistance into tobacco. Tobacco addition lines carrying the N. debneyi chromosomes with the gene for black root rot resistance were produced after two generations of backcrossing to the recurrent tobacco parent followed by two generations of selfing. Random amplified polymorphic DNA (RAPD) analyses of the disomic (2n = 50) addition lines and 14 monosomic (2n = 49) addition lines derived there from provided strong evidence that the two N. debneyi chromosomes in the 2n = 50 addition lines were identical. However, the tobacco genetic background apparently prevented homologous pairing of these chromosomes or caused their desynapsis. Lagging chromosomes at anaphase I and micronuclei at telophase I were observed. Transmission rates of the N. debneyi chromosomes through the egg and pollen of the addition lines were 8.1 and 10.1%, respectively. The N. debneyi chromosomes in the addition lines occasionally paired with tobacco chromosomes, and therefore, translocation lines with black root rot resistance (2n = 24 II) may be obtained in the self‐pollinated progeny by crossing‐over. Seventeen RAPD markers were found to be associated with the N. debneyi chromosomes in the addition lines and these should be useful in monitoring further transfer of N. debneyi chromosome fragments into the tobacco genomes.

Allozyme variation in populations, full-sib families and selfed lines in Betula pendula Roth

Changes in genetic variability in populations (stand origins), full-sib (FS) families and three generations of selfed lines of Betula pendula were observed based on 15 allozyme loci. Growth vigour, measured as stem volume, and its relationship with heterozygosity was studied to determine the effect of inbreeding. Pooled FS families showed a higher percentage of polymorphic loci (P) and allelic numbers per locus (A) than those of natural populations, but no difference in heterozygosity. There was no difference in allozyme variability between fast-and slow-growing family groups, and heterozygosity was not correlated with stem volume among FS families. Allozyme variability was significantly decreased in advancing generations of selfing, and the further the selfing generation, the lower the heterozygosity and the slower the growth. Observed heterozygosity after advancing generations of inbreeding was increasingly higher than expected, indicating overdominance effects or, alternatively, selection against deleterious homozygotes.

Growth performance of hybrid families by crossing selfed lines of Betula pendula Roth

Hybrid breeding is an effective approach in many agricultural crops. In allogamous tree species severe inbreeding depression and long reproductive cycles generally prohibit its use. However, three generations of selfing in silver birch (Betula pendula Roth) were obtained by forcing trees to flowering under greenhouse conditions. Hybrids were produced by crossing first-, second and third-generation selfed lines. The effects of different levels of parental inbreeding on the growth performance of hybrid families were observed in a 9-year-old field progeny test. Also, provenance crosses were carried out between selfed lines from different parts of Finland and several other European countries. Observations of growth performance of the provenance hybrids were made in the same trial. The results indicated that the mean stem volumes were significantly different between classes of parental in breeding coefficients (FP) (P<0.0001), and were positively correlated with FP (r=0.9106, P<0.05). Within-family variation of the hybrid families decreased with an increase of FP. The performance of the provenance crosses between parents at a relatively close distance did not depart significantly from the standard controls. However, when the cross distance was extended far to the south, hybrids grew faster, indicating either higher heterozygosity or an extended growth period.

Inbreeding depression under a competitive regime in Mimulus guttatus: consequences for potential male and female function

The effects of one generation of selfing and outcrossing on six life history characters were examined in the greenhouse for two populations of the mixed-mating species Mimulus guttatus. Inbreeding depression was not detected in the mass of seed produced by maternal plants, but selfing significantly reduced germination success by 13–20 per cent relative to outcross seeds. Seedlings produced by self-pollination were 26–31 per cent smaller than outcross progeny. Late life history stages were examined under varied competitive regimes in which each plant was grown with a neighbour of either an inbred or outbred individual. Progeny resulting from self-pollinations showed a 14–30 per cent reduction in ovule number per locule, and their pollen production per flower was reduced by 28–33 per cent. Adult above-ground biomass showed the greatest inbreeding depression, ranging from 24–50 per cent depending on the competitive conditions. Thus progeny resulting from selfing are smaller as adults and contribute significantly fewer potential gametes into the gene pool as pollen grains and ovules. The multiplicative effects of these characters is calculated. For all traits except ovule number, outcross progeny from parents of the same population did not differ significantly from outcross progeny produced by parents that came from populations separated by 10 km, suggesting relatively little differentiation between populations. The relative performance of self and outcross progeny in later life history stages was independent of the relative performance observed in earlier stages.

The Yd2 gene and enhanced resistance to barley yellow dwarf virus (BYDV) in winter barley

AbstractA breeding programme was developed to obtain barley yellow dwarf virus (BYDV)‐resistant winter genotypes using the Yd2 gene. The aim was to incorporate the Yd2 allele into the new high‐yielding genotypes to release cultivars that allow barley cultivation in areas where BYDV is endemic.The resistant lines were developed using pedigree selection. An ICARDA resistant line (83RCBB130) carrying the Yd2 gene was crossed with three susceptible, high‐yielding winter varieties and their F1 lines were either selfed or backcrossed to the matching susceptible parent. The best lines selected from subsequent selfing generations were evaluated in replicated trials in the presence or absence of BYDV, starting from F6 and BC1F5 to F8 and BC1F7 generations. Four genotypes with superior agronomic traits and BYDV resistance were selected.

Inbreeding depression in Lychnis flos‐cuculi (Caryophyllaceae): effects of different levels of inbreeding

AbstractIn a controlled crossing experiment on Lychnis flos‐cuculi plants in the greenhouse, outbred and selfed maternal plants were each treated with pollen from unrelated plants, siblings and selves. The seeds thus obtained had expected inbreeding coefficients of 0, 0.25 and 0.5 for the outbred maternal plants, and 0, 0.5 and 0.75 for the selfed maternal plants. Seed abortion rate, seed weight and germination rate were estimated. Seedlings were transplanted to an outdoor garden, and monitored for survival, probability of flowering, number of capsules and area of capsules next spring. Inbred seeds germinated slower and in lower proportions than those less inbred, and seedlings had lower survival, flowering, fruit set and area of capsules if inbred.Combined fitness values were estimated from the survival and fecundity components, and severe inbreeding depression was detected for these estimates (0.51 and 0.56 for one generation of selfing). The fitness function decreased linearly with the increase in inbreeding coefficient, which is as expected if the inbreeding depression is additive among loci.

Genetic variation and control of plant regeneration in leek (Allium ampeloprasum L.)

AbstractZygotic embryos of leek (Allium ampeloprasum L.) were isolated from mature seeds of different cultivars, selfings and full‐sib families. The embryos were cultured on callus induction and shoot regeneration medium and employed to study several parameters: percentage of embryos forming calluses, percentage of embryos forming compact calluses, callus weight, percentage of regenerating calluses, numbers of shoot primordia and numbers of regenerated shoots. Differences between cultivars and selfings were found for most parameters studied. For all cultivars all parameters, except callus weight, decreased after one generation of selfing. Compact callus types enhanced primordia formation and shoot regeneration. Genetic characteristics of callus development and plant regeneration were studied in a 4 × 4 diallel cross. Analysis of variance revealed significant differences between full‐sib families. The diallel analysis showed that additive gene effects were significant for all parameters. The predominance of additive gene effects indicated high narrow‐sense heritability. Breeding for an increased number of regenerated shoots was successful.

Pollen Heteromorphism inNicotiana tabacum (Solanaceae)

Pollen heteromorphism is defined as the production by a single plant of different fertile pollen types in all its anthers, and thus all flowers, throughout its life cycle. Eight cultivars of Nicotiana tabacum, as well as its ancestors (N. tabacum is an amphiploid hybrid 4 × from a cross between N. sylvestris and N. tomentosiformis) and recent hybrids were analyzed. Most cultivars and the hybrids are heteromorphic (producing 3‐ and 4‐aperturate pollen grains), whereas both parent species are homomorphic (3‐aperturate). Heteromorphism is a common consequence of polyploidization and these results agree with this interpretation. There is a significant variation in the proportions of the two pollen types among cultivars (genetic component), but also (with a much lower component of variance) within each cultivar, between plants (genets), flowers of a plant, and even anthers of a flower. This is interpreted as a release of the selective pressure: the cultivars of N. tabacum were obtained after several generations of selfing and are themselves selfers. Selfing, by removing pollen mixtures on a stigma, removes pollen competition, which is the drive for heteromorphism, and allows for a large variation of the proportions of the different pollen types.

Registration of Pearl Millet Parental Lines ICMA 88004 and ICMB 88004

The pearl millet (Pennisetum glaucum) line ICMB 88004 (PI583799) is a maintainer line of male sterile ICMA 88004 (PI583798), which is the seed parent of the single-cross grain hybrid ICMH 356. ICMA 88004 derives its A1 cytoplasm from 81A (ICMA 1); ICMB 88004 was developed by 10 generations of selfing in a half-sib progeny (Togo-11) of the same early maturing, large-seeded landrace from northern Togo that was the source of the commercial open-pollinated cv. ICTP 8203. In yield trials conducted in 11 year × location environments, ICMA 88044 gave a mean seed yield of 1.91 t/ha, required 49 days to 50% flowering and had a mean plant height of 1.4 m, which were similar to the highest-yielding commercial male-sterile line ICMA 841. ICMA 88004 is highly resistant to downy mildew (Sclerospora graminicola). ICMB 88004 is a prolific pollen producer, and is similar to ICMA 88004 in the above characters, except that it flowers 1-2 days later. Both lines express yellowish seedling foliage colour under daily maximum temperatures of <40°C. Recessive inheritance of this trait permits early detection and removal of offtype plants from seed production plots. These lines were released in 1993.