Induction of vivipary in Avena fatua

An investigation was conducted under controlled conditions to determine whether treatments designed to maximize the availability of water during seed development could induce viviparous germination in wild oats ( Avena fatua L.). Panicles of three genetic lines, which differed in their degree of dormancy, were kept in darkness at ca 100% RH and 20±1°C and were either supplied with water through the cut end of the rachis or left attached to the plant which was exposed to light. In the non-dormant line, germination of both primary and secondary caryopses on excised panicles increased with their stage of development when treated, i.e., 0, 5 and 10 days after anthesis. Germination of primary caryopses varied between 70 and 80% and was similar on both isolated and attached panicles treated at 10 and 5 days after anthesis, respectively. The percentage germination was considerably lower in all treatments of the two dormant lines and was inversely related to the genetically determined difference in their degree of dormancy. In these dormant lines germination was significantly lower on the intact plant than on the detached panicles. Water potential measurements suggested that this difference may be due partly to the transpiration-induced negative ψ_xyin the stem which may contribute to the inhibition of embryo growth and thus to the prevention of viparous germination.     

Metabolism of diclofop-methyl in cell cultures of Avena sativa and Avena fatua

The metabolism of the herbicide, diclofop-methyl (methyl-2-[4-(2', 4'-dichlorophenoxy) phenoxy]propanoate), in cell suspension cultures of Avena sativa L. (cv. Garry) and in callus of Avena fatua L. (transferred to liquid) was determined as a function of time (8 h to about 3 weeks) and was compared to previous metabolism data from intact plants. A. fatua metabolized ¹⁴C-labeled diclofop-methyl more rapidly than A. sativa, but the metabolites formed were similar if not identical. Within 2 days, approximately 50% of the total ¹⁴C recovered was in A. fatua cells whereas less than 15% was in A. sativa cells. In older cultures of A. fatua, the amounts of ¹⁴C in the cells and in the medium were about 45% each; 10 to 12% was in the non-extractable cell residue. The ¹⁴C recovered from A. sativa cells increased to a maximum of about 35% at 7 days and then slowly decreased to about 18% by 21 days, whereas the ¹⁴C in the medium of A. sativa decreased to about 60% at 7 days and then increased to over 75% by 21 days. The nonextractable ¹⁴C residue was 5% or less even after 21 days. Major metabolites in methanolic extracts of cells of both A. sativa and A. fatua were diclofop (2-[4-(2', 4'-dichlorophenoxy)phenoxy] propanoate), diclofop hydroxylated at an undetermined position on the 2,4-dichlorophenyl ring (ring OH-diclofop), and conjugates of diclofop and ring-OH diclofop.     

Path analysis of natural selection via survival and fecundity across contrasting environments in Avena barbata

We employed path analysis to analyse natural selection through two major fitness components in each of three contrasting environments. Using a randomized block design, 188 Recombinant Inbred Lines (RILs) derived from a cross between contrasting ecotypes of Avena barbata were planted in common gardens in the greenhouse, and in two field sites typical of each ecotype’s native habitat. Individuals were monitored for germination phenology, early growth, survival, final size, flowering phenology, reproductive allocation, fecundity and lifetime reproductive success. The variance/covariance matrix of the RIL (genotype) means was fit to a path model in which total fitness was made up of survival and fecundity (of survivors) components. In the greenhouse, all fitness variation was determined by fecundity variation (with no mortality), which was itself primarily determined by reproductive allocation mediated by date of first flowering. By contrast, in the field, early growth was the major determinant of survival, and final size was the major determinant of fecundity. Both components of fitness affected lifetime reproductive success equally in the field. Thus the major difference between greenhouse and field seems to be a shift from selection on allocation patterns in adults, to selection on resource acquisition, especially at earlier life stages. The pattern of selection was similar in the two field sites, despite the contrasting environments.     

Population biology of Avena XI. Variation in peripheral isolates of A. barbata

Data on genetic polymorphism, scored at two morphological loci, showed peripheral, isolated roadside colonies of slender oat (Avena barbata) to be significantly less polymorphic than the large central populations in continuous stands. The role of random drift (founder effect) was evident in the genetic structure of such roadside colonies which were, however, not monomorphic. Multilocus associations also suggested large Hill-Robertson effect in generating gametic disequilibria. Such isolates with varying amounts of elapsed time since the founder events could offer useful material for a study of evolutionary processes including the selection-drift balance.     

Herbicide resistance and gene flow in wild-oats (Avena fatua and Avena sterilis ssp. ludoviciana)

The process of resistance evolution to fenoxaprop-P-ethyl was investigated in the cereal weeds wild-oats (Avena fatua L. and Avena sterilis ssp. ludoviciana Malzew) at a number of locations in England, including one farm where distinct patches occur within fields. Genetic fingerprints produced using PCR-based techniques provided evidence for hybridisation between the species and that resistance had spread from one patch to others. The proportion of total variation due to differences between populations (G_st) was estimated at 33^2%, and herbicide-resistant patches contained on average less genetic diversity than herbicide-sensitive counterparts: both findings were consistent with a high degree of self-pollination. It was however concluded that cross-pollination occurs both within and possibly between species, and that this can result in the spread of herbicide resistance.     

A simulation model of Avena fatua L. (wild-oat) growth and development

An eco-physiological simulation model of the growth and development of Avena fatua was parameterised and tested. The model simulates growth ofA. fatua, in kg dry matter ha^-1 day^-1 from sowing to maturity as a function of irradiance, temperature and various species characteristics. Parameter values were derived from the literature and from field experiments, including both autumn and spring sowings of A. fatua over three years at two sites in southern England. With two exceptions, a single set of parameter values was sufficient to accurately simulate the emergence, growth and development of both autumn and spring cohorts over all years and sites. The two exceptions were the result of differences between autumn and spring cohorts of A. fatua in the rate of early leaf area growth and in the relationship between specific leaf area and developmental stage.     

Identifying loci under selection across contrasting environments in Avena barbata using quantitative trait locus mapping

We constructed recombinant inbred lines of a cross between naturally occurring ecotypes of Avena barbata (Pott ex Link), Poaceae, associated with contrasting moisture environments. These lines were assessed for fitness in common garden reciprocal transplant experiments in two contrasting field sites in each of two years, as well as a novel, benign greenhouse environment. An AFLP (amplified fragment length polymorphism) linkage map of 129 markers spanned 644 cM in 19 linkage groups, which is smaller, with more linkage groups, than expected. Therefore parts of the A. barbata genome remain unmapped, possibly because they lack variation between the ecotypes. Nevertheless, we identified QTL (quantitative trait loci) under selection in both native environments and in the greenhouse. Across years at the same site, the same loci remain under selection, for the same alleles. Across sites, an overlapping set of loci are under selection with either (i) the same alleles favoured at both sites or (ii) loci under selection at one site and neutral at the other. QTL under selection in the greenhouse were generally unlinked to those under selection in the field because selection acted on a different trait. We found little evidence that selection favours alternate alleles in alternate environments, which would be necessary if genotype by environment interaction were to maintain genetic variation in A. barbata. Additive effect QTL were best able to explain the genetic variation among recombinant inbred lines for the greenhouse environment where heritability was highest, and past selection had not eliminated variation.     

Within-family marker-assisted selection for aquaculture species

A within-family marker-assisted selection scheme was designed for typical aquaculture breeding schemes, where most traits are recorded on sibs of the candidates. Here, sibs of candidates were tested for the trait and genotyped to establish genetic marker effects on the trait. BLUP breeding values were calculated, including information of the markers (MAS) or not (NONMAS). These breeding values were identical for all family members in the NONMAS schemes, but differed between family members in the MAS schemes, making within-family selection possible. MAS had up to twice the total genetic gain of the corresponding NONMAS scheme. MAS was somewhat less effective when heritability increased from 0.06 to 0.12 or when the frequency of the positive allele was < 0.5. The relative efficiency of MAS was higher for schemes with more candidates, because of larger fullsib family sizes. MAS was also more efficient when male:female mating ratio changed from 1:1 to 1:5 or when the QTL explained more of the total genetic variation. Four instead of two markers linked to the QTL increased genetic gain somewhat. There was no significant difference in polygenic genetic gain between MAS and NONMAS for most schemes. The rates of inbreeding were lower for MAS than NON-MAS schemes, because fewer full-sibs were selected by MAS.     

Dormancy-associated embryonic mRNAs and proteins in imbibing Avena fatua caryopses

The mechanisms controlling seed dormancy maintenance and release are not understood. To characterize the molecular events accompanying dormancy release, two-dimensional gel electrophoresis was used to monitor changes in soluble proteins and in vitro translation products of embryonic mRNA populations during imbibition of dormant and nondormant (after-ripened) Avena fatua L. caryopses. No differences were observed between in vitro translation products of mRNA extracted from dry dormant and nondormant embryos. However, the expression patterns of several imbibition- and germination-associated mRNAs were temporally modulated during the first 24 h of imbibition. Two dormancy-associated mRNAs, represented by polypeptides D₁ and D₂, were differentially overexpressed in dormant embryos after 3 h of imbibition. mRNA levels for D₁ and D₂ were about 8- and 3-fold higher, respectively, in dormant embryos than in nondormant embryos after 3 h of imbibition. Overexpression of D₁ continued through 12 h of imbibition, while expression of both mRNAs fell to low and equivalent amounts in dormant and nondormant embryos after 24 h. Similar dormancy-associated changes in two soluble proteins were observed during imbibition. The results demonstrate that steady-state levels of specific mRNAs and proteins change during early imbibition of dormant and nondormant A. fatua embryos and indicate that these changes may be associated with differential gene expression responsible for the maintenance of dormancy.     

Metabolism of C-Maltose in Avena fatua Seeds During Germination

Non-dormant and dormant seeds of Avena fatua metabolize ¹⁴C-maltose in different ways: in non-dormant seeds, ¹⁴C-maltose administered to the endosperm is readily converted to sucrose in the scutellum and translocated to the embryo; in dormant seeds, little sucrose is synthesized from ¹⁴C-maltose, and maltose and glucose tend to accumulate in the endosperm. It is suggested that biosynthesis of sucrose is essential for effective transport of the endosperm reserve to the embryonic axis in germinating seeds.     

Developmental Differences Between Germinating After-ripened and Dormant Excised Avena fatua L. Embryos

Based on physiological and molecular differences associatedwith the germination of after-ripened and dormant caryopsesand excised embryos, it has been hypothesized that various methodsof after-ripening are the only treatments that facilitate thetransition of dormant wild oat embryos to a non-dormant state.To further investigate this hypothesis, analytical methods wereused to evaluate physical and temporal changes associated withgermination and subsequent growth of after-ripened and dormantexcised embryos (AR-embryos and D-embryos, respectively) inducedto germinate with fructose (Fru) and/or gibberellic acid (GA).While chemical treatments of Fru, GA, and Fru+GA have littleeffect on the germination and short-term growth of AR-embryos,they do induce germination of D-embryos. Growth following germinationof D-embryos varied according to treatment with the combinationof Fru+GA inducing the greatest growth over the duration ofthe experiment. Even considering differences in the time tocomplete germination, growth of D-embryos was not comparablewith that of AR-embryos. This provides physical evidence thatchemical treatments induce germination without fulfilling therequirements for normal after-ripening-enhanced germination/growth,and indicates that fructose and/or gibberellic acid do not removethe dormancy-block or rate limiting step in the same manneras after-ripening. Avena fatua ; after-ripening; dormancy; fructose; germination; gibberellic acid; wild oats     

Secondary dormancy in Avena fatua: Effect of temperature and after-ripening

To evaluate the effect of after-ripening on secondary dormancy induction in pure genetic lines of Avena fatua L., seed samples were periodically removed from standard conditions of storage and the caryopses then subjected to anoxia. Anoxia did not induce secondary dormancy in SH430, a line characterized by no primary dormancy at harvest maturity; secondary dormancy was induced in caryopses of other lines that had been after-ripened to over-come primary dormancy ranging in duration from a few days (CS40, CS166) to several months (AN51, AN127). Germination response to low GA₃ concentrations indicated that secondary dormancy in CS40 and CS166 was less intense than in AN51 and AN127. The longer the period of dry after-ripening prior to anoxia treatment, the lower the intensity of secondary dormancy induced. After a period of dry after-ripening, which was characteristic for each line, anoxia became an ineffective dormancy-inducing treatment. Caryopses selected for their response to dormancy induction by anoxia were subjected to temperatures from 5 to 35°C to investigate the effect of low (5 to 18°C) and high (20 to 35°C) temperatures on both thermo- and secondary dormancy induction. SH430 was not responsive to any treatment, while CS40, CS166 and AN51 were induced into a thermo-dormancy at temperatures above 20°C and CS166 and AN51 were induced into secondary dormancy by anoxia at temperatures from 5 to 35°C. The effect of anoxia on secondary dormancy induction in a range of pure genetic lines is discussed with reference to primary dormancy, after-ripening and temperature.     

The Germination of Avena fatua under Different Gaseous Environments

The atmosphere in which seeds germinate can profoundly affect the level of germination and dormancy. Seeds were germinated in atmospheres containing various concentrations of carbon dioxide and oxygen. At the same time the effect of light on these systems was examined. The germination of partially dormant populations of wild oat seed is inhibited by white light. This response to light is most apparent when the curyopsis is enclosed in the pales. Investigations into the effect of the ambient atmosphere on germination have indicated that, while oxygen is a necessary factor in the germination of tliis species, carbon dioxide also has an effect. A lack of carbon dioxide increases the degree of light inhibition of germination; 3 per cent carbon dioxide (by volume) allows germination in light; 20 per cent carbon dioxide inhibits germination in light and darkness at all tested oxygen concentrations.     

Action of Respiratory Inhibitors on Seed Germination and Oxygen Uptake in Avena fatua L.

The effects of sodium azide, potassium cyanide (cytochrome oxidaseinhibitors), and salicylhydroxamic acid (SHAM; an alternativerespiration inhibitor) on germination and respiration of Avenafatua L. seeds were studied. Azide and cyanide released seeddormancy at similar concentrations and treatment durations.Cyanide, however, stimulated germination of seeds with littleafter-ripening, whereas azide had no effect under similar conditionsunless the seeds were after-ripened for several months; theduration of after-ripening required for seeds to respond toazide varied with seed batch. There was also a greater lag priorto germination in the case of azide, compared to cyanide treatedseeds. SHAM inhibited the stimulation of germination and respirationby azide, but not by cyanide. Furthermore, respiration induced by azide or cyanide could notbe inhibited by the subsequent application of SHAM. These findingssuggest that the respiration stimulated by azide and cyanideis not alternative (SHAM-sensitive) and, therefore, this respiratorypathway cannot be involved in the stimulation of germinationby cytochrome oxidase inhibitors. While embryos excised fromcontrol, azide or cyanide pretreated seeds had the capacityto perform alternative respiration, the actual contributionof this pathway was negligible. A large proportion of respirationof embryos excised from azide or cyanide pretreated seeds wasresidual, i.e. insensitive to both SHAM and cyanide. Alternative respiration, azide, cyanide, dormancy, salicylhydroxamic acid, wild oats     

Genome structure and evolution in the allohexaploid weed Avena fatua L. (Poaceae).

Allohexaploid wild oat, Avena fatua L. (Poaceae; 2n = 6x = 42), is one of the world's worst weeds, yet unlike some of the other Avena hexaploids, its genomic structure has been relatively little researched. Consequently, in situ hybridisation was carried out on one accession of A. fatua using an 18S-25S ribosomal DNA (rDNA) sequence and genomic DNA from A. strigosa (AA-genome diploid) and A. clauda (CC-genome diploid) as probes. Comparing these results with those for other hexaploids studied previously: (i) confirmed that the genomic composition of A. fatua was similar to the other hexaploid Avena taxa (i.e., AACCDD), (ii) identified major sites of rDNA on three pairs of A/D-genome chromosomes, in common with other Avena hexaploids, and (iii) revealed eight chromosome pairs carrying intergenomic translocations between the A/D- and C-genomes in the accession studied. Based on karyotype structure, the identity of some of these recombinant chromosomes was proposed, and this showed that some of these could be divided into two types, (i) those common to all hexaploid Avena species analysed (3 translocations) and (ii) one translocation in this A. fatua accession not previously observed in reports on other hexaploid Avena species. If this translocation is found to be unique to A. fatua, then this information, combined with more traditional morphological data, will add support to the view that A. fatua is genetically distinct from other hexaploid Avena species and thus should retain its full specific status.     

Growth and development of Avena fatua (Wild-oat) in the field

The growth and development of field-grown Avena fatua plants were studied for autumn and spring sowings in two consecutive years. The duration of various growth stages from sowing until anthesis was quantified in terms of thermal time (accumulated degree days) or photothermal time (degree days modified by photoperiod). Base temperatures and photoperiods for developmental phases were estimated as those which minimised the coefficient of variation among sowing dates. Relationships were derived between leaf emergence, canopy height, plant leaf area, and photothermal time. Stem extension and flowering occurred earlier in autumn-sown plants than spring-sown plants. Autumn-sown plants produced more leaves on the main stem, and had greater leaf area and above-ground biomass at anthesis than spring-sown plants.     

一粒小麦-葡萄牙野燕麦远缘杂交后代衍生系GISH研究

以一粒小麦-葡萄牙野燕麦杂交后代一粒葡为实验材料,以地高辛标记的葡萄牙野燕麦基因组DNA为探针、一粒小麦基因组DNA为封阻对一粒葡及其衍生系根尖染色体进行基因组原位杂交(GISH)分析,探讨了影响一粒葡GISH效果的主要因素.建立并优化了一粒葡GISH分析的实验体系,即探针DNA与封阻DNA比例为1∶50时可有效分开双方染色体组.优化GISH分析显示,在一粒葡后代衍生系中均检测到燕麦染色质的存在,且不同选系间带有燕麦染色体的数目不同,进一步证明一粒葡是一粒小麦-葡萄牙野燕麦远缘杂交的后代.     

Zur Keimungsphysiologie des Wildhafers (Avena fatua L.)

The density of the phytophagous curculionid weevil complex belonging to one family and four subfamilies was determined in three different ecotypes including date‐palm, vegetable and natural (fallow) habitats in Western Saudi Arabia. Different densities were observed in the three habitats during 1996–1997. However, the date palm habitat showed high number of curculionid weevils. This may be attributed to the availability of food source, vegetational cover and shaded environment in the available niche. Chi square test showed that there were significant differences in density numbers between the three habitats. Three peaks were observed in the date‐palm habitat during December, March and May.