Conferring resistance to pre-harvest sprouting in durum wheat by a QTL identified in <Emphasis Type="Italic">Triticum spelta</Emphasis>

Pre-harvest sprouting (PHS) causes significant yield loss and degrade the end-use quality of wheat, especially in regions with prolonged wet weather during the harvesting season. Unfortunately, the gene pool of Triticum durum (tetraploid durum wheat) has narrow genetic base for PHS resistance. Therefore, finding out new genetic resources from other wheat species to develop PHS resistance in durum wheat is of importance. A major PHS resistance QTL, Qphs.sicau-3B.1, was mapped on chromosome 3BL in a recombinant inbred line population derived from ‘CSCR6’ (Triticum spelta), a PHS resistant hexaploid wheat and ‘Lang’, a PHS susceptible Australian hexaploid wheat cultivar. This QTL, Qphs.sicau-3B.1, is positioned between DArT marker wPt-3107 and wPt-6785. Two SCAR markers (Ph3B.1 and Ph3B.2) were developed to track this major QTL and were used to assay a BC₂F₈ tetraploid population derived from a cross between the durum wheat ‘Bellaroi’ (PHS susceptible) and ‘CSCR6’ (PHS resistant). Phenotypic assay and marker-assisted selection revealed five stable tetraploid lines were highly PHS resistant. This study has successfully established that PHS-resistance QTL from hexaploid wheat could be efficiently introgressed into tetraploid durum wheat. This tetraploid wheat germplasm could be useful in developing PHS resistant durum cultivars with higher yield and good end-use quality.     

Introgression of <Emphasis Type="Italic">Gossypium barbadense</Emphasis> L. into Upland cotton germplasm RMBUP-C4S1

Gossypium barbadense L. cotton has significantly better fiber quality than Upland cotton (G. hirsutum L.); however, yield and environmental adaptation of G. barbadense is not as wide as Upland. Most cotton in the world is planted to Upland cultivars. Many attempts have been made, over a considerable number of years, to introgress fiber quality alleles from G. barbadense into Upland. However, introgression barriers, primarily in the form of interspecific incompatibility, have limited these traditional approaches. The use of chromosome substitution lines (CSL) as a bridge should provide a more efficient way to introgress alleles from G. barbadense into Upland. We crossed 18 G. barbadense CSL to three cultivars and developed a random mated population. After five cycles of random mating followed by one generation of self-pollination to increase the seed supply, we grew the random mated population and used 139 G. barbadense chromosome specific SSR markers to assess a random sample of 96 plants for introgression. We recovered 121 of 139 marker loci among the 96 plants. The distribution of the G. barbadense alleles ranged from 10 to 28 alleles in each plant. Among the 96 plants we found individual plants with marker loci from 6 to 14 chromosomes or chromosome arms. Identity by descent showed little relatedness among plants and no population structure was indicated by a heat map. Using CSL we were able to develop a mostly Upland random mated population with considerable introgression of G. barbadense alleles which should be useful for breeding.     

Identification and validation of root length QTLs for water stress resistance in hexaploid wheat (<Emphasis Type="Italic">Titicum aestivum</Emphasis> L.)

Thorough understanding of the genetic mechanisms governing drought adaptive traits can facilitate drought resistance improvement. This study was conducted to identify chromosome regions harbouring QTLs contributing for water stress resistance in wheat. A RIL mapping population derived from a cross between W7984 (Synthetic) and Opata 85 was phenotyped for root length and root dry weight under water stress and non-stress growing conditions. ANOVA showed highly significant (p ≤ 0.01) variation among the RILs for both traits. Root length and root dry weight showed positive and significant (p ≤ 0.01) phenotypic correlation. Broad sense heritability was 86% for root length under stress and 65% for root dry weight under non-stress conditions. A total of eight root length and five root dry weight QTLs were identified under both water conditions. Root length QTLs Qrln.uwa.1BL, Qrln.uwa.2DS, Qrln.uwa.5AL and Qrln.uwa.6AL combined explained 43% of phenotypic variation under non-stress condition. Opata was the source of favourable alleles for root length QTLs under non-stress condition except for Qrln.uwa.6AL. Four stress specific root length QTLs, Qrls.uwa.1AS, Qrls.uwa.3AL, Qrls.uwa.7BL.1 and Qrls.uwa.7BL.2 jointly explained 47% of phenotypic variation. Synthetic wheat contributed favourable alleles for Qrls.uwa.1AS and Qrls.uwa.3AL. Two stable root dry weight QTLs on chromosomes 4AL and 5AL were consistently found in both water conditions. Three validation populations were developed by crossing cultivars Lang, Yitpi, and Chara with Synthetic W7984 to transfer two of the QTLs identified under stress condition. The F_2.3 and F_3.4 validation lines were phenotyped under the same level of water stress as RILs to examine the effect of these QTLs. There were 13.5 and 14.5% increases in average root length due to the inheritance of Qrls.uwa.1AS and Qrls.uwa.3AL, respectively. The result indicated that closely linked SSR markers Xbarc148 (Qrls.uwa.1AS) and Xgwm391 (Qrls.uwa.3AL) can be incorporated into MAS for water stress improvement in wheat.     

Development of NBS-related microsatellite (NRM) markers in hexaploid wheat

NBS (nucleotide binding site) genes, one type of the most important disease-resistance genes in the plant kingdom, are usually found clustered in genome. In this study, a total of 2288 full-length NBS protein-coding sequences were isolated from the wheat (Triticum aestivum L.) genome, and 903 TaNBSs of which were found expressed in wheat. Meanwhile, 2203 microsatellite loci were detected within 1061 scaffolds containing TaNBS. The distribution of these microsatellite loci across wheat homologous groups (HG) is 20% HG2, 16% HG7, 15% HG1, 15% HG6, 12% HG4, 12% HG5 and 10% HG3. We developed 1830 NBS-related microsatellite (NRM) markers for the microsatellite loci on TaNBS-scaffold sequences.Among them, 342 NRM markers were developed for HG2 with the largest number of microsatellite loci, and 69 out of these markers were anchored to the wheat genetic map using mapping population. Then, a total of 26 2AS-NRM markers, nine 2BL-NRM markers and nine 2DL-NRM markers were integrated into the genetic maps carrying Yr69, Pm51 and Pm43, respectively. Finally, candidate sequences, within the gene clusters where Yr5 and Sr21 located, were analyzed according to the genomic position information of TaNBS and NRM markers. These NRM markers have clear chromosome locations and are correlated with potential disease resistance sequences, which can be manipulated to mapping or adding linkage markers of disease-resistance genes or QTLs, especially for those in the NBS gene clusters.     

Effects of <Emphasis Type="Italic">Solanum demissum</Emphasis> chromosomes on crossability in the backcross progeny to <Emphasis Type="Italic">Solanum tuberosum</Emphasis>

A balance of maternal and paternal genetic factors, conceptually named the endosperm balance number (EBN), is required for normal endosperm development in interspecific crosses in potato. We previously found that Solanum demissum (D), a hexaploid wild species widely used in potato breeding, has a slightly lower EBN than S. tuberosum (T). To explore the genetic nature of the EBN, the berry-setting rate, seed number/berry, and seed weight were evaluated in BC₁ [(D?×?T)?×?T] plants, each possessing different portions of the S. demissum chromosomes, by reciprocal crosses with D and T, and a quantitative trait locus (QTL) analysis was performed. At least 99 S. demissum-derived QTLs were detected, of which 29 were associated with differential responses to D and T. Three QTLs were possibly co-localized on chromosomes 7A and 10D1, while the remaining 23 QTLs were independently located. The QTLs in the three S. demissum homoeologous chromosomes exhibited three types of interaction: (1) positive, (2) negative, and (3) one positive and one negative effect on the same trait. We found that several major genes, one of which was localized in the S. demissum chromosome 9A, and many minor genes controlled the crossability of BC₁ plants. The QTLs responsible for the differential responses to D and T were different between the BC₁ plants used as male and female parents, indicating that different genes control the male and female EBNs. Consequently, we conclude that the EBN is represented by the sum of various genetic effects controlled by a large number of genes.     

Allelic variation at the gliadin coding loci of improved Ethiopian durum wheat varieties

The objective of this study was to determine gliadin allele compositions of 20 improved Ethiopian durum wheat varieties using acid-polyacrylamide gel electrophoresis (A-PAGE). Each block of co-dominantly inherited polypeptides encoded by gliadin loci were identified and their genetic diversities were estimated using statistical analyses. A total of 30 electrophoretic blocks were identified at five major gliadin loci. In addition, four novel gliadin blocks were identified. Gli-B1 and Gli-A2 loci had higher numbers of gliadin alleles (nine and ten, respectively) compared to other loci. Alleles Gli-A1c on chromosome 1A, Gli-B1c on chromosome 1B, Gli-A2a, and Gli-A2o on chromosome 6A, and Gli-B2h on chromosome 6B had maximal frequencies in their corresponding loci. Varieties were classified into three main clusters and one singleton based on genetic distances of detected gliadin alleles. These results indicate that Ethiopian durum wheat varieties are genetically diverse with unique allele compositions at gliadin-coding loci.     

Mapping QTLs with epistatic effects and QTL × treatment interactions for salt tolerance at seedling stage of wheat

Quantitative trait loci (QTLs) with additive (a), additive × additive (aa) epistatic effects, and their treatmental interactions (at and aat) were studied under salt stress and normal conditions at seedling stage of wheat (Triticum aestivum L.). A set of 182 recombinant inbred lines (RILs) derived from cross Xiaoyan 54 × Jing 411 were used. A total of 29 additive QTLs and 17 epistasis were detected for 12 traits examined, among which eight and seven, respectively, were identified to have QTL × treatment effects. Physiological traits rather than biomass traits were more likely to be involved in QTL × treatment interactions. Ten intervals on chromosomes 1A, 1D, 2A (two), 2D, 3B, 4B, 5A, 5B and 7D showed overlapping QTLs for different traits; some of them represent a single locus affecting different traits and/or the same trait under both treatments. Eleven pairs of QTLs were detected on seemingly homoeologous positions of six chromosome groups of wheat, showing synteny among the A, B and D genomes. Ten pairs were detected in which each pair was contributed by the same parent, indicating a strong genetic plasticity of the QTLs. The results are helpful for understanding the genetic basis of salt tolerance in wheat and provide useful information for genetic improvement of salt tolerance in wheat by marker-assisted selection.     

<Emphasis Type="Italic">Er3</Emphasis> gene,conferring resistance to powdery mildew in pea,is located in pea LGIV

Three genes for resistance to Erysiphe pisi, named er1, er2 and Er3 have been described in pea so far. er1 gene is located in pea linkage group VI, while er2 gene has been mapped in LGIII. SCAR and RAPD markers tightly linked to Er3 gene have been identified, but the position of these markers in the pea genetic map was unknown. The objective of this study was to localize Er3 gene in the pea genetic map. Towards this aim, the susceptible pea cv. Messire (er3er3) and a resistant near isogenic line of Messire (cv. Eritreo, Er3Er3) were surveyed with SSRs with known position in the pea map. Three SSRs were polymorphic between “Messire” and “Eritreo” and further surveyed in two contrasting bulks formed by homozygous Er3Er3/er3er3 individuals obtained from a F₂ population derived from the cross C2 (Er3Er3)?×?Messire (er3er3). A single marker, AA349, was polymorphic between the bulks. Subsequently, other ten markers located in the surrounding of AA349 were selected and analysed in Er3Er3 and er3er3 plants. As a results, another SSR, AD61, was found to be polymorphic between Er3Er3 and er3er3 plants. Further linkage analysis confirmed that SSRs AA349 and AD61 were linked to Er3 and to the RAPD and SCAR markers previously reported to be linked to this gene. Er3 gene was located in pea LGIV at 0.39 cM downstream of marker AD61. The location of Er3 gene in the pea map is a first step toward the identification of this gene.     

Mapping QTL for stay-green and agronomic traits in wheat under diverse water regimes

Wheat (Triticum aestivum L.) yield is directly proportional to physio-morphological traits. A high-density genetic map consisting of 2575 markers was used for mapping QTL controlling stay-green and agronomic traits in wheat grown under four diverse water regimes. A total of 108 additive QTL were identified in target traits. Among them, 28 QTL for chlorophyll content (CC) were detected on 11 chromosomes, 43 for normalized difference vegetation index (NDVI) on all chromosomes except 5B, 5D, and 7D, five for spikes per plant (NSP) on different chromosomes, nine for plant height (PH) on four chromosomes, and 23 for thousand-kernel weight (TKW) on 11 chromosomes. Considering all traits, the phenotypic variation explained (PVE) ranged from 3.61 to 41.62%. A major QTL, QNDVI.cgb-5A.7, for NDVI with a maximum PVE of 20.21%, was located on chromosome 5A. A stable and major PH QTL was observed on chromosome 4D with a PVE close to 40%. Most distances between QTL and corresponding flanking markers were less than 1 cM, and approximately one-third of the QTL coincided with markers. Each of 16 QTL clusters on 10 chromosomes controlled more than one trait and therefore could be regarded as pleiotropic regions in response to different water regimes. Forty-one epistatic QTL were identified for all traits having PVE of 6.00 to 25.07%. Validated QTL closely linked to flanking markers will be beneficial for marker-assisted selection in improving drought-tolerance in wheat.     

Development and application of PCR markers specific to the 1Ns chromosome of Psathyrostachys huashanica Keng with leaf rust resistance

Wheat–Psathyrostachys huashanica Keng disomic addition line 12-3 was developed and characterized using genomic in situ hybridization (GISH), expressed sequence tag–sequence tagged site (EST–STS), and sequence characterized amplified region (SCAR) markers. Mitotic and meiotic GISH analyses indicated that it contained 42 wheat chromosomes and a pair of P. huashanica chromosomes. Eight EST–STS multiple-loci markers located on the homoeologous group 1 chromosomes of wheat amplified polymorphic bands in the 1Ns disomic addition line 12-3, which were unique to P. huashanica. These markers suggested that the introduced Ns chromosomes belonged to homoeologous group 1. Furthermore, diagnostic fragments of random amplified polymorphic DNA marker OPAG10₉₈₆ and simple sequence repeat marker Xgwm601 ₁₃₅ were cloned, sequenced, and converted into SCAR markers, i.e., RHS153 and SHS10, respectively, which were validated using a range of distinct plant species and a complete set of wheat–P. huashanica disomic addition lines (1Ns–7Ns, 2n = 44 = 22 II). The results demonstrated that the SCAR markers targeted the Ns genome of P. huashanica and they were linked to the 1Ns chromosome. In addition, 12-3 was evaluated to test its leaf rust resistance in the adult stages and its agronomic traits. These newly developed EST–STS and SCAR markers will be powerful tools for wheat breeders who want to screen for genotypes containing the 1Ns chromosome, with low costs and high throughput.     

Effects of introgressions from <Emphasis Type="Italic">Festuca pratensis</Emphasis> on winter hardiness of <Emphasis Type="Italic">Lolium perenne</Emphasis>

Previous studies reported that some genotypes with introgressed Festuca chromosome segment(s) in Lolium genome showed enhanced winter hardiness compared to Lolium. The aim of this study was to search comprehensively for the Festuca pratensis chromosome regions affecting winter hardiness-related traits when introgressed into the Lolium perenne genome. Association between F. pratensis introgression and winter hardiness-related traits (fall and winter hardiness indexes, early-spring dry matter yield, and freezing tolerance) were screened in the diploid introgression populations (n = 203) that had some F. pratensis chromosome segments introgressed. Eighty-four intron markers corresponding to unique rice genes randomly distributed across the genome were used for genotyping. Winter hardiness of almost all plants in the introgression populations was lower than that of the F. pratensis and triploid hybrid parents, but the average was higher than that of L. perenne. A significant positive effect of F. pratensis introgression on early-spring dry matter yield was detected on chromosome 7. This quantitative trait locus (QTL) was confirmed by linkage analysis using a backcross population with F. pratensis introgression in the target region of chromosome 7. However, the contribution of the newly identified QTL was rather small (6.7–9.6%), suggesting that superior winter hardiness of F. pratensis compared to L. perenne is conferred by multiple small-effect QTLs. We also detected a previously unreported negative effect of Festuca introgression on winter hardiness. Newly obtained QTL information in this study would contribute to the design of Festuca/Lolium hybrid breeding.     

Asparagine synthetase genes (<Emphasis Type="Italic">AsnS1</Emphasis> and <Emphasis Type="Italic">AsnS2</Emphasis>) in durum wheat: structural analysis and expression under nitrogen stress

Wheat is one of the most widely grown cereal crops based on the amount of calories it provides in the human diet. Durum wheat (Triticum turgidum ssp. durum) is largely used for production of pasta and other products. In order to use genetic knowledge to improve the understanding of N-use efficiency, we carried out, for the first time in durum wheat, the isolation and the characterization of four members of the asparagine synthetase (AsnS) gene family. Phylogenetic inference clustered the Ttu-AsnS1 (1.1 and 1.2) and Ttu-AsnS2 (2.1 and 2.2) genes in AsnS gene class I, which is present in monocots and dicots. Class I genes underwent a subsequent duplication leading to the formation of two subgroups. Plants of Svevo cultivar were grown under N-stress conditions and expression of the four AsnS genes was investigated at three developmental stages (seedling, booting, and late milk development), crucial for N absorption, assimilation and remobilization. AsnS1 genes were down-regulated in N-stressed roots, stems and leaves during seedling growth and booting, but seemed to play a role in N remobilization in flag leaves during grain filling. AsnS2 genes were scarcely expressed in roots, stems, and leaves. In N-stressed spikes there was no differential expression in any of the genes. The genes were mapped in silico using a durum wheat SNP map, assigning Ttu-AsnS1 genes to chromosome 5 and Ttu-AsnS2 to chromosome 3. These findings provide a better understanding of the role of ASN genes in response to N stress in durum wheat.     

QTL for flag leaf size and their influence on yield-related traits in wheat

Flag leaf-related traits (FLRTs) are determinant traits affecting plant architecture and yield potential in wheat (Triticum aestivum L.). In this study, three related recombinant inbred line (RIL) populations with a common female parent were developed to identify quantitative trait loci (QTL) for flag leaf width (FLW), length (FLL), and area (FLA) in four environments. A total of 31 QTL were detected in four environments. Two QTL for FLL on chromosomes 3B and 4A (QFll-3B and QFll-4A) and one for FLW on chromosome 2A (QFlw-2A) were major stable QTL. Ten QTL clusters (C1–C10) simultaneously controlling FLRTs and yield-related traits (YRTs) were identified. To investigate the genetic relationship between FLRTs and YRTs, correlation analysis was conducted. FLRTs were found to be positively correlated with YRTs especially with kernel weight per spike and kernel number per spike in all the three RIL populations and negatively correlated with spike number per plant. Appropriate flag leaf size could benefit the formation of high yield potential. This study laid a genetic foundation for improving yield potential in wheat molecular breeding programs.     

Development of a core set of SSR markers for the characterization of <Emphasis Type="Italic">Gossypium</Emphasis> germplasm

Molecular markers such as simple sequence repeats (SSR) are a useful tool for characterizing genetic diversity of Gossypium germplasm. Genetic profiles by DNA fingerprinting of cotton accessions can only be compared among different collections if a common set of molecular markers are used by different laboratories and/or research projects. Herein, we propose and report a core set of 105 SSR markers with wide genome coverage of at least four evenly distributed markers per chromosome for the 26 tetraploid cotton chromosomes. The core marker set represents the efforts of ten research groups involved in marker development, and have been systematically evaluated for DNA polymorphism on the 12 genotypes belonging to six Gossypium species [known collectively as the cotton marker database (CMD) panel]. A total of 35 marker bins in triplex sets were arranged from the 105 markers that were each labeled with one of the three fluorescent dyes (FAM, HEX, and NED). Results from this study indicated that the core marker set was robust in revealing DNA polymorphism either between and within species. Average value of polymorphism information content (PIC) among the CMD panel was 0.65, and that within the cultivated cotton species Gossypium hirsutum was 0.29. Based on the similarity matrix and phylogenetic analysis of the CMD panel, the core marker set appeared to be sufficient in characterizing the diversity within G. hirsutum and other Gossypium species. The portability of this core marker set would facilitate the systematic characterization and the simultaneous comparison among various research efforts involved in genetic diversity analysis and germplasm resource preservation.     

Genome-wide detection of genetic loci associated with soybean aphid resistance in soybean germplasm PI 603712

Soybean aphid (Aphis glycines Matsumura) has become one of the major pests of soybean [Glycine max (L.) Merr.] in North America since 2000. At least four biotypes of soybean aphid have been confirmed in the United States. Genetic characterization of new sources of soybean aphid resistance will facilitate the expansion of soybean gene pool for soybean aphid resistance and thus will help to develop soybean aphid resistant cultivars. To characterize the genetic basis of soybean aphid resistance in PI 603712, a newly identified resistant germplasm line, 142 F₂ plants derived from the cross ‘Roberts’ × PI 603712 and their parents were evaluated for soybean aphid resistance in the greenhouse, and were genotyped with BARCSoySNP6K Illumina Infinium II BeadChip. A genome-wide molecular linkage map was constructed with 1495 polymorphic SNP markers. QTL analysis revealed that PI 603712 possessed two major loci associated with soybean aphid resistance, located on chromosome 7 and 16, respectively. The locus on chromosome 7 was dominantly expressed and positioned about one Mega-base-pair distant from the previously identified resistance locus Rag1. The locus on chromosome 16 was positioned near the previously identified resistance locus Rag3 and expressed partially dominance or additive effect. Interestingly, two minor loci were also detected on chromosomes 13 and 17 but the alleles from PI 603712 decreased the resistance. In developing soybean aphid resistant cultivars through marker-assisted selection, an appropriate combination of resistance loci should be selected when PI 603712 is used as a donor parent of resistance.     

Developing and validating microsatellite markers in elephant grass (<Emphasis Type="Italic">Pennisetum purpureum</Emphasis> S.)

Elephant grass [Pennisetum purpureum S.; syn. Cenchrus purpureus (Schumach.) Morrone] is an important global forage crop and is recognized for high yields of herbage with good nutritive value. It also has high biomass potential to be utilized as a biofuel feedstock. Whereas several previous genetic studies adapted simple sequence repeat (SSR) markers from pearl millet [Pennisetum glaucum (L.) R.Br.] for investigations in elephant grass, the present study developed SSR markers from 3536 DNA sequences derived from 16 elephant grass entries. A total of 3866 SSRs were identified including 1028 monomeric, 2019 dimeric, 735 trimeric, 49 tetrameric, 20 pentameric and 15 hexameric repeat motifs. Three hundred and seven sequences contained more than one repeated motif, and 154 SSRs were present in compound formation. Susequenctly,  four elephant grass and two pearl millet genotypes were chosen to validate 727 SSR markers. Of these, 628 markers produced visually detectable amplification products, including 73 (11.6%) polymorphic ones across all six genotypes. Polymorphism between the four elephant grass genotypes was revealed by 316 (50.6%) markers with diversity index values ranging from 0.75 to 0.38. Dimeric SSRs had the highest polymorphic rate (48.7%). These validated SSR markers had 58.6% (368 of 628) transferability rate to pearl millet. The availability of these polymorphic SSR markers will support advanced genetic studies in P. purpureum and its relatives.     

Allelic composition and associated quality traits of the <Emphasis Type="Italic">Glu-1</Emphasis> and <Emphasis Type="Italic">Glu-3</Emphasis> loci in selected modern Ethiopian durum wheat varieties

Gluten protein determines the processing quality of both durum wheat and bread wheat. The glutenin subunits compositions and associated quality traits of 20 Ethiopian durum wheat varieties were systematically analyzed using SDS-PAGE and Payne numbers. A total of 16 glutenin patterns were identified. At the Glu-A1 locus, all varieties scored the null allele. The predominant glutenin alleles at the Glu-B1 locus were Glu-B1b (7+8) and Glu-B1e (20). In Glu-3, the most abundant glutenin subunits were Glu-A3a and Glu-B3c. Based on the Payne scores, the varieties Yerer, Ginchi, Candate, and Foka were identified to have allelic composition suitable for pasta making. The cluster analysis using agglomerative hierarchical clustering (AHC) method classified the varieties into four similarity classes. Based on the findings of this experiment, suggestions were made for allelic composition improvement through introgression of superior alleles from known Glu-1 and Glu-3 sources.     

Cereal cytogenetics in retrospect. What came true of some cereal cytogeneticists' pipe dreams?

Achievements and limitations regarding three aspects of cytogenetic research in barley and common wheat are illustrated and discussed. Unambiguous chromosome identification has become possible through the application of chromosome banding techniques, mainly C-banding, N-banding and Ag-banding. Gene localisation studies have yielded a vast amount of information regarding the genetic architecture of barley and wheat. Many genes have been allocated to specific chromosomes, and linkage studies have been carried out with some of these genes. There is growing evidence for a considerable discrepancy between distances on the genetic linkage maps and the physical maps of barley and wheat chromosomes. Although barley can be hybridised with most species of the genus Hordeum and with several species of related genera, interspecific gene transfer is very rare and barley breeding can presently make use of the gene pool of only one wild species, viz. H. vulgare ssp. spontaneum. For wheat breeding, the gene pools of species of the genus Triticum and species of related genera are accessible. Several methods have been developed to achieve gene transfer. Genome interactions in interspecific hybrids result in spatial separation of the parental genomes, in nucleolar competition, and sometimes in chromosome elimination and the formation of haploids.     

Screening <Emphasis Type="Italic">A. ventricosa</Emphasis> populations for 2n gametes

Sexual polyploidization via the formation of 2n gametes has been acknowledged as the most significant evolutionary mode of polyploidization among plant species. The present study was conducted in order to determine whether 2n gametes are present in the C-genome diploid Avena ventricosa Bal. ex Coss., a species that contributed to the evolution of the cultivated hexaploid species (Avena sativa L). Individual plants belonging to four different Cypriot populations, were screened for pollen grain size variation with the aim to distinguish 2n gametes. Avena ventricosa ARI00-845 was identified to produce large pollen grains at a low percentage (1.21%). Subsequent analysis using flow cytometry confirmed the presence of 2n gametes in the pollen. Cytogenetic analyses of pollen mother cells revealed cells with twice the typical chromosome number at metaphase I (i.e., 28 chromosomes). We postulate that irregularities in cell wall formation preceding meiosis could have contributed to the mode of chromosome doubling.     

Development of RAPD and ISSR derived SCAR markers linked to <Emphasis Type="Italic">Xca1Bo</Emphasis> gene conferring resistance to black rot disease in cauliflower (<Emphasis Type="Italic">Brassica oleracea</Emphasis> var. <Emphasis Type="Italic">botrytis</Emphasis> L.)

Black rot caused by Xanthomonas campestris pv. campestris (Xcc) (Pam.) is the most devastating disease of cauliflower (Brassica oleracea var. botrytis L.; 2n = 2x = 18), taking a heavy toll of the crop. In this study, a random amplified polymorphic DNA (RAPD) and inter simple sequence repeat (ISSR) derived sequence characterized amplified region (SCAR) markers linked to the black rot resistance locus Xca1bo were developed and evaluated as a screening tool for resistance. The RAPD marker OPO-04₈₃₃ and ISSR marker ISSR-11₆₃₅ were identified as closely linked at 1.6 cM distance to the black rot resistance locus Xca1bo. Both the markers OPO-04₈₃₃ and ISSR-11₆₃₅ were cloned, sequenced and converted into SCAR markers and validated in 17 cauliflower breeding lines having different genetic backgrounds. These SCAR markers (ScOPO-04₈₃₃ and ScPKPS-11₆₃₅) amplified common locus and showed 100% accuracy in differentiating resistant and susceptible plants of cauliflower breeding lines. The SCAR markers ScOPO-04₈₃₃ and ScPKPS-11₆₃₅ are the first genetic markers found to be linked to the black rot resistance locus Xca1bo in cauliflower. These markers will be very useful in black rot resistance marker assisted breeding.