Avena Species Research Articles

Variation in the kernel (1 → 3) (1 → 4)-β- D-Glucan content of oat cultivars and wild Avena species and its relationship to other characteristics

Kernel (1 → 3) (1 → 4)-β-n-glucan, kernel protein and mean kernel size have been estimated in six cultivars of oats ( Avena sativa ) L, and eight wild Avena species grown at two levels of nitrogen fertility in a pot experiment. In the oat cultivars, kernel protein and kernel β-glucan were both increased at the higher nitrogen fertility level. Comparison with the results from field grown material which had still higher kernel protein contents indicated that this association between β-glucan and protein occurred over a wide range of kernel protein levels. However cultivar differences were more distinct at lower fertility levels. Six of the eight Avena species had a mean kernel size that was substantially lower than the cultivars. However the protein contents of the Avena species were in general higher and they showed a wider range of β-glucan contents. Although higher nitrogen fertility increased grain protein in the wild species, β-glucan was only significantly increased in one species. Kernel β-glucan content was independent of both kernel protein and mean kernel size in the wild species. Results show that phenotypic variations in kernel protein are associated with concomitant variations in β-glucan in oat cultivars and furthermore that wild Avena species may be useful additional sources of variation for this characteristic.

A repeated sequence probe for the C genome in Avena (Oats)

The genus Avena consists of at least 23 species composed of three ploidy levels. Cytogenetic analysis has characterised four distinct karyotypes. These are the A, B, C and D genomes. We have isolated a repeated sequence clone that can be used for the detection of the C genome in Avena by filter hybridization techniques. This clone, termed RS-1, is a genomic DNA clone containing at least one highly repeated sequence that is abundant in Avena species containing the C genome. This sequence or a related sequence is also present, but at much reduced levels, in species that do not contain the C genome. Because of its abundance and the characteristic Southern blot pattern, we have termed this clone a C genome specific clone. We have also done similar analysis of the Avena genus using a rDNA clone from wheat. The results of these experiments demonstrate that clearly definable C genome-specific markers can be identified with both probes. These molecular probes can be useful in studying the genomic relationships of Avena and can provide some clues as to the origin of the cultivated Avena species. These results can, therefore, provide breeders with directions for the efficient transfer of desirable traits of wild Avena species into commencal varieties.

Synaptonemal complex formation in Avena polyploids

Avena maroccana (2n = 4x = 28) and A. sativa (2n = 6x = 42) are allopolyploids. Reconstructions from electron micrographs of synaptonemal complexes in serial sections of pollen mother cells showed that associations at zygotene and subsequent stages of meiosis are confined to homologous chromosomes only, with the result that only bivalents are generated. Such “classical” behaviour contrasts sharply with that in allopolyploids of wheat, Lolium and Scilla. In these pairing at zygotene involves homoeologous as well as homologous chromosomes, generating not only bivalents but multivalents which are “resolved” to bivalents prior to first metaphase. An analysis is presented, also, of structural and genetic factors which influence the distribution of pairing within and between chromosomes at zygotene in the Avena species.

Analysis of avenin proteins and the expression of their mRNAs in developing oat seeds.

We have isolated and characterized cDNA clones encoding avenins, the prolamine storage proteins of oat seeds. Sequence analysis shows that avenins are a related group of polypeptides and that their mRNAs differ from each other by point mutations and small insertions and deletions. Avenin proteins have structural homology to the alpha/beta-gliadins and gamma-gliadins of wheat, the B-hordeins of barley, and the gamma-secalins of rye. Hybridization analysis of DNA from various diploid, tetraploid, and hexaploid oat species shows that the oat genome contains more globulin storage protein genes than avenin genes and that some restriction fragments containing these genes are conserved between species with common genomes. We estimate that there are 25 avenin genes and 50 globulin genes per haploid genome in Avena sativa and similar ratios of globulin to avenin genes in other Avena species. Avenin and globulin polypeptides begin to accumulate between 4 days and 6 days after anthesis. Messenger RNAs encoding avenin and globulin proteins become abundant 4 days after anthesis and reach peak concentrations at 8 days after anthesis. Avenin mRNAs are present in somewhat greater molar amounts than globulin mRNAs beginning at 4 days after anthesis. Because there is considerably more globulin than avenin in the mature oat seed, the expression of globulin and avenin genes may be regulated both transcriptionally and post-transcriptionally.

Studies of isozymes in oat species

Starch and polyacrylamide gel electrophoresis of seven isozyme systems was investigated as a means of identifying wild and cultivated species of Avena with different ploidy levels. By examining the characteristic isoenzymatic patterns, it was shown that there was considerable variability within the different species. However, it was nevertheless possible to unequivocally identify the species of wild oats and to distinguish between the different species belonging to the same genomic set, thus providing a definitive reference technique for the identification of Avena species in seed-testing laboratories. The relationships between Avena species were inferred from the electrophoresis data. The divergence of the A. maroccana - A. murphyi complex and its contribution to the AACC genomes are emphasized.

Genomic Affinity Relationships in the Genus Avena

AbstractMany interspecific hybrids between diploid, tetraploid and hexaploid Avena species were obtained without artificial embryo cultures. Most of the hybrids showed variable chromosome pairing with univalents, bivalents and multiple associations, even in PMC in the same hybrid, at first metaphase; making ii very difficult to understand the degree of genome affinity between parent species, and especially between different species. The basic or theoretical chromosome pairing consisting of bivalents and univalents is presented, in which the chromosome ratios (%) statistically agree with observations. In addition, the per cent frequency of chromosomes forming multivalents is calculated. On the bases of these numerical data, the genomic affinity relationships are discussed for present and previously reported interspecific hybrids or Avena.

Flavonoid variations in Avena species

Twenty-five Avena species were investigated for their flavonoids. The flavonoids identified were vitexin, isovitexin, vitexin 2″-rhamnoside, isovitexin 2″-arabinoside, isoswertisin 2″-rhamnoside, tricin 5-glucoside, tricin 7-glucoside and tricin 7-diglucoside. Chemosystematic relationships are discussed.

Immunocytological and chemical studies on the stromacentre-forming protein from Avena plastids

The stromacentre (SC), a particular structure in the plastids of Avena, was isolated from etioplasts of Avena sativa by density gradient centrifugation and then analyzed and compared with ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBPCase) from A. sativa, with pyrenoids of Chlorella vulgaris and with the "stromacentre" of Opuntia. Purified SC-elements consisted of protein subunits with a relative molecular weight of 63 kDa, different from the isolated RuBPCase of A. sativa as shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After peptide mapping, the proteolytic cleavage patterns of the 63-kDa protein were also found to be different from those of the RuBPCase. Antibodies against SC-elements, RuBPCase, and the large subunit of RuBPCase were produced. Ouchterlony double immunodiffusion tests did not give crossreactions between the SC-elements and RuBPCase or the large subunit of this enzyme. Immunogold labelling of ultrathin sections showed that antibodies against the SC-elements marked the stromacentre in Avena, but not the pyrenoids in Chlorella. Antibodies against the large subunit of RuBPCase, however, did not label the SC, but labelled the stroma of the plastids in Avena and the pyrenoids of Chlorella. In Opuntia, a comparable structure described as an SC was not labelled by any of the antisera. Immunoelectrophoretical investigations demonstrated a strong correlation between the presence of the 63-kDa protein and the occurrence of the SC in different Avena species with and without SC.

Screening for resistance against rhopalosiphum padi (L.). I. avena species and breeding lines

Thirty-two accessions of Avena species and breeding lines were evaluated for resistance, primarily antibiosis, to the aphid Rhopalosiphum padi (L.) in greenhouse and growth room tests. The highest levels of resistance were found in A. barbata and in the perennial species A. macrostachya. One breeding line, Obee, was also found to have interesting resistance characters. Resistance in A. macrostachya is discussed in relation to perenniality. A different screening method for rapid testing of large collections of varieties is evaluated.

Phosphorus-containing Compounds at Comparable Germination Stages of Caryopses of Avena Species

A number of the phosphorus transformations accompanying imbibition and initial germination in caryopses of wild oats (A vena fatua L.) differ in nature and kind from those accompanying seedling development. Even in non-dormant lines of wild oat germination is extended and seedling development uneven. The significance of early phosphorus transformations can be obscured. Procedures to synchronize germination stages were developed by (i) using seeds which had been exposed to room temperature for extended periods of dry storage, (ii) inducing germination of imbibed seeds by dehulling, piercing and/or gibberellin A3 treatments, or (iii) constructing artificial seed groupings of known germination percentage by appropriate selection of seeds from an unevenly germinating seed source. All three procedures were effective in identifying those processes associated with initial germination. The best synchronization was obtained with method (i). Germination, in contrast to imbibition, was signalled by a significant drop in inorganic phosphate levels, followed by a later rise as seed reserves of phytate were mobilized for seedling development. Differences in the rates of mobilization of acid-soluble phosphorus compounds were apparent between cultivated oats and genetically non-dormant wild oats.

ELECTROPHORETIC PATTERNS OF OAT PROLAMINES AND SPECIES RELATIONSHIPS IN AVENA

Starch gel electrophoretic studies on seed prolamines of 17 different di-, tetra-, and hexaploid Avena species were undertaken to determine species relationships and the evolutionary process of the polyploids. Significant intraspecific variation was observed. Electrophoregrams of each species were obtained by superposing all the bands found in the same species and in total, 17 bands were observed. Clear differences were found between species in their patterns, which allowed determination of the bands specific to three genomes (A, C and D). Like the diploids, the tetraploids can be divided into two groups on the basis of electrophoretic patterns: A. barbata and A. magna-A. murphyi. It is evident that A. magna-murphyi group is derived from both the A and C genome species of diploids while A. barbata is derived from the A genome species only. The similarity between A. magna and A. murphyi was also confirmed. The hexaploids were derived from A. magna-murphyi group and a D genome ancestor although the last one is not discovered yet.

Population Biology of Avena. VII. Allozyme Variation in Relation to the Genome Analysis

Genetic similarity (GS) among 15 Avena species was analyzed by scoring allozyme variation. The presence versus absence of a total of 73 bands for EST, LAP, APX, and CPX was tallied for approximately 3,000 plants from 218 populations. Variation among populations of the same species was highly significant. After pooling of data for all its populations, each species could be characterized by certain diagnostic sites, using the presence/absence patterns. The GS among species, taken pairwise, was measured by the proportion of common bands. Estimates of the similarity indices (SIs) suggested that genome relationships postulated from cytogenetic and morphological-ecogeographical studies in Avena are largely confirmed by the allozyme variation patterns. Genome formulas from cytogenetic and morphological work show divergence among the diploid species and putative ancestry of tetraploids and hexaploids. Allozyme patterns in this study are consistent with these genome relationships in that SIs among the diploids w...

Triple fusion of the primary endosperm nucleus as a cause of interspecific cross-incompatibility in Avena

Using five diploid, two tetraploid and three hexaploid Avena species (x=7) 78 reciprocal crosses were made. Of these 74 were successfull, though the frequency of seed set varied greatly. The development of hybrid seeds differed widely between cross combinations, especially in reciprocal crosses. Hybrid seeds were grouped into four types, (1) normal kernels, well developed and germinative (designated as D+); (2) shrivelled-empty kernels, which do not germinate (E−); (3) small viable kernels (Rd+) and (4) small inviable kernels (Rd−). Some rare intermediate types were found in certain crosses. The results are well interpreted in terms of a hypothesis of polar-nuclei activation in which the strength of the activating action of the male nucleus, and the reaction of the female nucleus at double fertilization are expressed as ‘activating value(AV)’ and ‘response value(RV)’, respectively. The degree of seed failure is closely related to the activation index(AI) of the polar nuclei, AV/2RV (or × 100). In a selfed plant the activation index is always 1/2=0.5 (or50%), and this usually results in the formation of normal seeds. If AI deviates from 50% the endosperm often stops developing or degenerates. Based on the degree of abnormality of hybrid seeds, activating values of the ten species were arbitrarily assigned from 0.4 in A. ventricosa (2x) to 3.0 in A.sterilis (6x). For comparison A.strigosa (2x) was used as a standard and set at 1.0. Among the 74 succesful interspecific crosses the AI of the polar nuclei varied widely, from 7 to 375% Generally speaking, AI values of less than 20, 20–30, 30–80, and more than 80% show the R-, Rd+, D+ and E-kernel types, respectively. In other words, if the AV of the pollen parent is 160% that of the maternal parent hybrid seeds fail to develop. Thus in double fertilization of Avena or probably angiosperms, the triple fusion of two polar nuclei with a secondary male nucleus is apparently a sexual isolation mechanism, being a barrier to interspecific hybridization.

Intranuclear fibrillar material in cereal pollen mother cells

Ultrastructural studies of cereal anthers found intranuclear bundles of microfilaments in pollen mother cells (PMCs) but not elsewhere. The ultrastructure, distribution, and behaviour of this fibrillar material (FM) are described. FM was seen in all 19 genotypes studied comprising Aegilops, Triticum, Secale, Hordeum and Avena species, which together included haploid, diploid and allo-and autopolyploid, and natural and synthetic polyploid examples. Detailed studies in diploid S. cereale, and hexaploid T. aestivum and Triticale showed that FM was present in PMC nuclei during premeiotic interphase, leptotene and zygotene but not at pachytene and later meiotic stages. Moreover, it was most abundant at late premeiotic interphase in T. aestivum, and at leptotene in S. cereale and Triticale, when it occurred in up to 100% of sampled PMC nuclei in an anther. Although FM and synaptonemal complex (SC) occurred together in some PMC nuclei at later stages, FM was present long before SC, and reached its peak of abundance before SC did. Bundles of FM often formed links at their ends between either two masses of chromatin, or more rarely, between chromatin and the nuclear membrane. Individual bundles of FM varied in length but showed roughly similar ranges of lengths and widths in these three species. They were up to about 0.2 μm in diameter and about 3 μm in length, equivalent to about 20% of the maximum diameter of the nuclei containing them. Reconstructions of PMC nuclei indicated that FM was never associated with centromeres but was sometimes, and perhaps usually, associated with telomeric or sub-telomeric chromosome segments.

Population biology of avena. VI. The role of genetic polymorphisms in the outcome of interspecific competition

Three different series of population samples of two Avena species cooccurring in California were grown for an analysis of the role of genetic variation in interspecies competition: I, samples from mixed fatua-barbata sites in nature, grown in mixed stands; II, samples from pure sites and grown in pure stands, and III, the same sites as in II but grown in mixed stands. Four macroenvironments and four densities were used giving a total of sixteen entries for each genetic/competitive unit in order to measure both mean and variance of survival and reproductive rates as fitness characters. Sites used in each series included low versus high levels of genetic polymorphism within each species. In general, high polymorphism favored A. fatua in competition with monomorphic A. barbata, and high polymorphism in A. barbata allowed it to compete better with monomorphic A. fatua observation fits well into the pattern of reduced polymorphism in natural mixed stands. Mean performance of polymorphic mixed stands was not consistently higher than the monomorphic combinations or pure stands but the greater relative stability over environments seemed to favor polymorphisms in one or both of the competitors. A relatively less regular pattern of density or competitive response in series III was interpreted as evidence for the lack of coadaptedness between samples drawn from pure sites. Several limitations characteristic of such controlled studies were briefly discussed; however, the tentative conclusions from laboratory studies provided several promising clues for more critical field studies.

Interspecific cross-incompatibility due to disturbed activation of the polar nuclei by the male nucleus

A total of 74 interspecific reciprocal crosses was made among ten polyploid species of Avena. The development of hybrid kernels was very variable, and grouped into four types, Rd -, Rd +, D + and E - which indicate small or very small, small, mormal and empty, shrivelled kernels, respectively, as vvell as germination (+) and non-germination (-) of hybrid kernels. In a small number of crosses, however, some intermediate types of kernels were found. The results are almost completely explained in terms of a hypothesls of polar-nuclei activation by the male nucleus in double fertilization. The strength of stimulus of the male nucleus and reaction of the female nucleus is expressed by terms activating value (AV) and value (RV), respectively. Activating values assigned to Avena species show a range from 0.4 to 3 where 1 to A. strigosa is standard. The degree of seed failure is closely related to the differenec between activatlng and response value which usually is represented by an activation index (AI) of the polar nuclei. The AI is c, omputed from a formula, AV/2 RV (or X100%), In a plant selfed the AI is 1/2=0.5 (or 50%), being a normal index, and resultlng in production of normal seeds. If AI deviates from 50% the development of endosperm is often arrested, and it causes the seed abortlon in the extreme case. In the present hybridizations the activation index varies greatly from 7 to 375%Expressing in round numbers less than 20, 90-30, 30-80 and more than 80% activation indexes show Rd -, Rd +, D + and E - type kernels, res-pectively. Those of intermediate-type kernels are always found on boundary zones between the four groups. In other ¥vords, it is shortly stated that interspecific crosses of Avena are only compatible when their activation indexes fall within a range from 20 to 80 % .Thus the triple fusion of the two pdlar nuclei with the male nucleus In angiosperms seems to be a sexual isolation mec.hanism and the most efffective barrier to interspecific hybridizations.

Nuclear and cytoplasmic genome relationships in the genus Avena: analysis by isoelectric focusing of ribulose biphosphate carboxylase subunits.

Comparisons of the isoelectric points of small and large subunits of ribulose biphosphate carboxylase extracted from a number of diploid, tetraploid, and hexaploid Avena species have been used to obtain information on the nuclear and cytoplasmic genome relationships within the genus. All species tested had small subunits with similar isoelectric points, so their analysis provided no information of taxonomic value. Three types of large subunits could be distinguished by this method, and the distribution of each among the available species provides strong evidence against the involvement of a C genome diploid (such as A. ventricosa) as the maternal parent in the formation of either tetraploid or hexaploid species. One type of large subunit was confined to the perennial tetraploid, A. macrostachya, and its position in the genus and possible origin are discussed. The value of this approach in studying genome relationships within the genus Avena and related genera is assessed.

Assessment of Cladograms Obtained for Fourteen Species of Avena by Two Methods of Numerical Analysis

A data set consisting of 14 Units (EU's), diploid Avena species, was used to compare the results obtained by two numerical cladistic methods. Cladograms were obtained from Farrns' method of computing Wagner trees and from Estabrook's compatibility and cliques approach. Only afew cladogramsfrom each method are similar. It is maintained that in any cladistic study a number of different analyses should be made, using various methods, so that the most plausible cladogram can be selected. The choice is subjective to a degree, and the needfor optimality criteria for making that choice is stressed. The purpose of this paper is to compare the results obtained by two different methods of cladistic analysis on diploid Avena species. One method is by Farris' (1970) for computing Wagner trees and the other is Estabrook's (Estabrook & Fiala, 1975) based on compatibility analysis and generation of cliques. There are fundamental differences between the two methods. From the user's point of view the most important difference is that in Estabrook's approach the directions of evolutionary trends must be provided by the investigator for each character tree whereas this is not a requisite in Farris' method. There are also other details and differences in assumptions, approaches, and algorithms (Estabrook, 1968, Estabrook et al., 1975, 1976; Kluge & Farris, 1969; Farris, 1969, 1970). The results using Farris' method have been published previously (Baum, 1975) for a different purpose. MATERIALS AND METHODS Fourteen Units (EU's) were selected from species of Avena. The concept Evolutionary Unit has been discussed and defined 1 I thank G. F. Estabrook for permission to use COMPATIBILITY and J. S. Farris for permission to use CLAD/OS. 2 Biosystematics Research Institute, Research Branch, Agriculture Canada, Ottawa, Ontario KIA 0C6, Canada. 141 This content downloaded from 157.55.39.45 on Wed, 05 Oct 2016 05:24:45 UTC All use subject to http://about.jstor.org/terms 142 SYSTEMATIC BOTANY [Volume 2

The Distribution of Avena Species Naturalized in Western Australia

The Distribution of Avena Species Naturalized in Western Australia

Host and environmental effects on the penetration of oats by Puccinia graminis avenae and Puccinia coronata avenae

SUMMARYThe frequency of penetration from appressoria of Puccinia graminis avenae and P. coronata avenae varied among Avena species and between oat cultivars, although both rusts produced susceptible infection type pustules on the cultivars tested. Penetration on cv. Garry was significantly less than that on the Avena species (A. barbata, A.fatua and A. sterilis) studied and penetration of these Avena species was significantly less than on the cvs Algerian and Fulmark. When the rusts were allowed to develop into pustules on seedlings which had been inoculated with fixed amounts of inoculum, there was a direct relationship between number of pustules produced and penetration frequency.The effects of temperature, light and dew period on penetration from appressoria of ‘single race’ and ‘mixed race’ inocula was also studied on these cultivars and species. Penetration by P. graminis avenae was greatest at 30–35 °C and at light intensities of 5625 lux and above, whereas that by P. coronata avenae was greatest at 20 °C and was unaffected by artificial light intensities up to n 250 lux. Maximal penetration by P. graminis avenae and P. coronata avenae was observed after inoculated plants had been exposed to dew periods of 16 and 12 h respectively. Some penetration was observed after a dew period of 8 h. The time taken for each rust to attain maximum penetration varied from 36 to 52 h after inoculation, depending on the environment, and was usually less for P. coronata avenae than for P. graminis avenae.