New Diversity Arrays Technology (DArT) markers for tetraploid oat (Avena magna Murphy et Terrell) provide the first complete oat linkage map and markers linked to domestication genes from hexaploid A. sativa L.

Nutritional benefits of cultivated oat (Avena sativa L., 2n = 6x = 42, AACCDD) are well recognized; however, seed protein levels are modest and resources for genetic improvement are scarce. The wild tetraploid, A. magna Murphy et Terrell (syn A. maroccana Gdgr., 2n = 4x = 28, CCDD), which contains approximately 31% seed protein, was hybridized with cultivated oat to produce a domesticated A. magna. Wild and cultivated accessions were crossed to generate a recombinant inbred line (RIL) population. Although these materials could be used to develop domesticated, high-protein oat, mapping and quantitative trait loci introgression is hindered by a near absence of genetic markers. Objectives of this study were to develop high-throughput, A. magna-specific markers; generate a genetic linkage map based on the A. magna RIL population; and map genes controlling oat domestication. A Diversity Arrays Technology (DArT) array derived from 10 A. magna genotypes was used to generate 2,688 genome-specific probes. These, with 12,672 additional oat clones, produced 2,349 polymorphic markers, including 498 (21.2%) from A. magna arrays and 1,851 (78.8%) from other Avena libraries. Linkage analysis included 974 DArT markers, 26 microsatellites, 13 SNPs, and 4 phenotypic markers, and resulted in a 14-linkage-group map. Marker-to-marker correlation coefficient analysis allowed classification of shared markers as unique or redundant, and putative linkage-group-to-genome anchoring. Results of this study provide for the first time a collection of high-throughput tetraploid oat markers and a comprehensive map of the genome, providing insights to the genome ancestry of oat and affording a resource for study of oat domestication, gene transfer, and comparative genomics.

Domestication via hybridization of the wild tetraploid oats Avena magna and A. murphyi.

The wild tetraploid (2n=28) oat species Avena magna and A. murphyi have been domesticated by having been transferred from the common oat, A sativa (2n=42), the characteristics of non-shedding spikelets glabrous and yellow lemma, and reduced awn formation. Domestication has been achieved by crossing the common oat with either of the tetraploid species and then backcrossing the pentaploid hybrids with pollen of the tetraploid wild parent. Among the BC plants obtained only a few produced some seeds. Fertile tetraploids exhibiting the domesticated syndrome have been selected for in the F2 generation. Although morphologically they were almost indistinguishable from the common oat, they were tetraploids. Wild x domesticated A. magna hybrids were vigorous and fertile. They retained their spikelets at maturity, lemma color and pubescence were intermediate between the parental lines, and awns were formed only on the lower floret of the spikelet. Each of these characteristics segregated in a 3∶1 fashion, indicating single gene control, as in the common oat. These four characteristics formed a linkage group in one F2 family and two linkage groups in the other two families. The usefulness of the domesticated tetraploids for oat research and production has been discussed. Taxonomically, the domesticated tetraploids were ranked as subspecies: A. magna ssp. domestica, and A. murphyi ssp. rigida.

Inheritance and linkage relationships of morphological and isozyme loci in chickpea (Cicer arietinum L.).

Inheritance and linkage relationships of several morphological and isozyme loci are described in chickpea (Cicer arietinum L.). Segregation data obtained from several F2 families confirmed the previously observed mode of inheritance for most of the morphological loci. Additional morphological markers in chickpea are also described. Most of the isozyme loci studied showed codominant expression and fit expected Mendelian segregation ratios. However, distorted ratios were also observed for some loci. Linkage was found betweenPgd-c, the locus encoding the cytosolic form of 6-phosphogluconate dehydrogenase, andHg, the locus controlling plant growth habit. These 2 loci were separated by approximately 18 recombinational map units. A similar linkage between comparable loci was previously reported in pea (Pisum sativum L.) (Weeden and Wolko 1990). Linkage was also detected among 3 isozyme loci; the cytosolic form of phosphoglucomutase (Pgm-c), glucose-1-phosphate transferase (Gpt1), and the plastid specific form of 6-phosphogluconate dehydrogenase (Pgd-p). The linkage of 2 loci (Pgm-c andPgd-p) in this cluster is also conserved in pea and lentil (Lens Miller). The linkage between an acid phosphatase locus (Acp3) and the locus specifying the cytosolic form of glucosephosphate isomerase (Gpi-c) in chickpea suggested another linkage group in common with pea. Additionally, other linkages that were not previously observed in chickpea or related genera included the linkage of the cytosolic form of aconitase (Aco-c) with adenylate kinase (Adk1) and fructokinase (Fk3), and the linkage of a locus encoding the mitochondrial specific aconitase (Aco-m) with a seed protein locus (Spr1). The loci determining flower color (P), epicotyl color (Gst), seed coat color (T (3)), and seed surface (Rs) were associated with the locus encoding glucose-1-phosphate transferase (Gpt2). These results, along with previous studies, suggest that pea, lentil and chickpea have several common linkage groups consisting of homologous genes. This also indicates that linkages found in one genus can be used to predict similar linkages in related genera in the development of linkage maps.

Genetic diversity and adaptedness in tetraploid Avena barbata and its diploid ancestors Avena hirtula and Avena wiestii.

Avena barbata, a tetraploid grass, is much more widely adapted and successful in forming dense stands than its diploid ancestors. The success of such polyploids has often been attributed to heterosis associated with ability to breed true for a highly heterozygous state in which allelic differences between the parents are fixed in the polyploid by chromosome doubling. We have examined the relationship between genetic diversity and adaptedness for 14 allozyme loci in A. barbata and its diploid ancestors in samples collected from diverse habitats in Israel and Spain. The relationship varied from locus to locus: superior adaptedness was associated with genetic uniformity for five loci, in part with genetic uniformity and in part with genetic diversity (monomorphism for a single heteroallelic quadriplex) for one locus, and with allelic diversity in the form of heteroallelic quadriplexes combined with genotypic diversity in the form of complex polymorphisms among different homoallelic and/or heteroallelic quadriplexes for the eight remaining loci. These results indicate that allelic diversity fixed in nonsegregating form through chromosome doubling was an important factor in the evolution of adaptedness in A. barbata. However, it is unlikely that heterosis associated with heterozygosity contributed significantly to superior adaptedness in either the diploids or the tetraploid because virtually all loci (approximately 99%) were homozygous in the Avena diploids and tetraploid.

Genetic mapping of an ancient translocation in the genus Lens.

Segregation of 18 marker genes was monitored in selfed progeny of a Lens culinaris × L. ervoides hybrid; five linkage groups were mapped, one of which contained a reciprocal translocation break-point that differentiates between the parents. Four markers were found to be linked to the translocation break-point: Aco-1 and Pgm-2 on one side and Gs and Got-2 on the other. The gene pairs on both sides of the translocation are not linked in L. culinaris or in L. orientalis. The L. ervoides gene order was also found in L. odemensis but with significantly reduced map distances. Analysis of monogenic segregations in a number of Lens inter-specific crosses revealed some consistent patterns of deviations from the expected Mendelian ratios. The factors responsible for these unequal segregations, genotypic effects on recombination frequencies, negative interference, and the possible ancient origin of the translocation are discussed.

Phylogenetic studies in Papaver section Oxytona: cytogenetics of the species and interspecific hybrids.

Chromosome behaviour at meiosis was studied in the F1, F2, and backcross generations, in the three species of Papaver section Oxytona, and in artificially induced autopolyploids of P. bracteatum. Close homology was found between the genome of P. bracteatum and that of the two polyploid species, P. orientale and P. pseudo-orientale, suggesting that the P. bracteatum genome is present in both polyploid species. A genetic mechanism controlling bivalent pairing in the polyploid species is suggested. Further study is needed for finding out the breeding potential of interspecific hybridization in section Oxytona.

Hybridization in the genus Lens by means of embryo culture.

The cultivated lentil L. culinaris and the wild lentil L. ervoides are reproductively isolated from one another due to their hybrid embryo breakdowns. Using embryo culture, vegetatively normal hybrids were obtained. One specific hybrid, heterozygous for a reciprocal translocation, had about 50% gamete viability and produced aborted and viable embryos in a 1∶1 ratio. In the F2, vegetatively normal and highly fertile plants were selected. With the aid of embryo culture techniques, L. ervoides can be included in the wild gene pool of the cultivated lentil.

Lycopersicon esculentum: Trifoliate plants recovered from anther cultures of heterozygous tftf plants.

The effects of the genotype and growth medium composition on callus induction and shoot regeneration from tomato (Lycopersicon esculentum Mill) anthers were studied. Five male sterile varieties, homozygous for the recessive gene ms 10(35), their isogenic fertile counterparts, and nineteen sterile mutants from an F2 population segregating for ms 10(35), were tested. Callus induction and shoot formation were found to be affected by the genotype. The presence of the mutant gene ms 10(35) greatly increased callus induction. A significant interaction concerning callus induction was found between the ms 10(35) gene and the general genetic background. In most of the plants shoot regeneration from the anthers was associated with various degrees of callus production. However, there was no correlation between callus production and the ability to regenerate plants from that callus. Anthers isolated from plants which were heterozygous for the recessive leaf marker trifoliate, regenerated diploid plants with trifoliate leaves. The plants retained the trifoliate phenotype for over six months in culture under non-aseptic condition. Since the trifoliate phenotype appears only in the homozygous recessive state, the evidence that these trifoliate plants are doubled haploids of sporogenic origin is discussed.

Seed protein electrophoresis in taxonomic and evolutionary studies.

Seed protein electrophoresis is increasingly being utilized as an additional approach for species identification and as a useful tool for tracing back the evolution of various groups of plants. This paper summarizes the main features of the seed protein profile - stability, uniformity and additive nature. In addition, the significance of this approach for resolving specific taxonomic and evolutionary problems is pointed out.

The cytogenetic structure of Vicia sativa aggregate.

The cytogenetic structure of Vicia sativa aneuploid series was assessed by examination of the chromosome pairing in hybrids between types having 2n = 10, 2n = 12 and 2n = 14. Two different karyotypes were distinguished at both the 2n = 10 and 2n = 12 levels. Chromosome pairing in hybrids involved two 2n = 10 karyotypes, indicating that the parental lines differed by two translocations. A similar indication was obtained for the two 2n = 12 karyotypes employed. The meiotic behavior of the 2n = 10 x 2n = 12 hybrids indicated that the parental lines differed by up to three translocations, some of which involved unequal chromosome segments. It has been proposed that the 2n = 10 types were developed from the 2n = 12 via centric or tandem fusion and additional rearrangements further accelerated chromosome repatterning at the two 2n levels. Hybrids between the 2n = 14 V. sativa and the former 2n types had very irregular chromosome pairing and were highly sterile. It has been proposed that the 2n = 14 type is a relatively new evolvement in V. sativa because of its shorter complement in comparison with the other karyotypes. The subterraneous pods of the 2n = 14 type, a characteristic which is absent in other V. sativa types and in the entire genus Vicia, also supports an advanced, phylogenetic position. The 2n = 14 type probably arose from n = 7 gametes produced by the 2n= 12 x 2n = 10 hybrid and the establishment of the row 2n = 14 type was acquired through conspicuous chromosome deletions. In spite of its remarkable chromosomal variation, V. sativa can still be considered, for breeding purposes, as being one gene pool. The wild forms of V. sativa can thus be valuable sources for improving the cultivated vetch.

A case of genome partition in polyploid oats.

At the second generation of the interspecific cross between the cultivated hexaploid (2n = 42) oat A. Sativa and the wild tetraploid (2n = 28) A. Murphyi, a plant having hexaploid and diploid (2n = 14) sectors was selected. Meiosis was highly regular in the diploid sector but the tillers failed to proceed beyond the boot stage and no seeds were produced. It is suggested that this diploid sector represents an entire genome of one of the diploid progenitors of the hexaploid oat.

Genetic relationships among the annual species of Cicer L.

Genetic relationships between 7 annual species of the genus Cicer, including the cultivated chickpea, have been studied. These species were assigned to 3 crossability groups. In each group interspecific hybrids could be obtained but their fertility differed considerably in the various cross combinations. Crosses between members of different groups yielded no viable seeds. The possibility of gene transfer from the wild species to the cultivated chickpea C. arietinum was also assessed. Only two species could be considered for this purpose, C. reticulatum, which is the wild progenitor of the cultivated species, and C. echinospermum, which is in the secondary gene pool of C. arietinum. A unique postzygotic reproductive barrier mechanism was found between the members of Group II, C. judaicum, C. pinnatifidum and C. bijugum. It is based on a disharmony in the growth rate of the stigma and the anthers at the time of anthesis of the F(1) interspecific hybrid so that selfpollination is avoided. It is proposed that this kind of mechanism has been involved only when an effective spatial isolation between the three species had been obtained.