Molecular-marker analysis of quantitative traits for growth and development in juvenile apple trees

Random amplified polymorphic DNAs (RAPDs) were used in combination with a double pseudo-testcross mapping strategy to estimate the position and effects of quantitative trait loci (QTLs) for traits influencing juvenile tree growth and development in two apple cultivars. The mapping population consisted of 172 F₁ trees from a cross between the columnar mutant ‘Wijcik McIntosh’ and a standard form disease-resistant selection NY 75441-58. Significant associations were found between markers and height increment, internode number, internode length, base diameter increment, base diameter after 9 years of growth, branch number, and leaf break. The number of genomic regions associated with each trait varied from one to eight. The amount of variation explained by linear regression on individual marker loci (R²) ranged from 3.9 to 24.3%, with an average of 7%. Multiple regression using markers for each putative QTL explained from 6.6 to 41.6% of the phenotypic variation, with an average value of 24.3%. A large number of traits had significant variation associated with the map position of the dominant columnar gene, Co. QTL stability over years was estimated by comparing the locations of putative QTLs for traits measured in multiple years. The majority of genomic regions were associated with a trait in only a single year, although regions associated with a trait in more than 1 year were also detected. The limitations of dominant markers and an outbred mapping pedigree for QTL analysis are discussed. Received: 27 August 1997 / Accepted: 10 February 1998     

Development of an STS map of an interspecific progeny of Malus

Simple sequence repeat (SSR) markers developed from Malus, as well as Prunus, Pyrus and Sorbus, and some other sequence-tagged site (STS) loci were analysed in an interspecific F₁ apple progeny from the cross ‘Fiesta’ × ‘Totem’ that segregated for several agronomic characters. A linkage map was constructed using 259 STS loci (247 SSRs, four SCARs and eight known-function genes) and five genes for agronomic traits—scab resistance (Vf), mildew resistance (Pl-2), columnar growth habit (Co), red tissues (Rt) and green flesh background colour (Gfc). Ninety SSR loci and three genes (ETR1, Rt and Gfc) were mapped for the first time in apple. The transferability of markers from other Maloideae to Malus was found to be around 44%. The loci are spread across 17 linkage groups, corresponding to the basic chromosome number of Malus and cover 1,208 cM, approximately 85% of the estimated length of the apple genome. Interestingly, we have extended the top of LG15 with eight markers covering 25 cM. The average map density is 4.7 cM per marker; however, marker density varies greatly between linkage groups, from 2.5 in LG14 to 8.9 in LG7, with some areas of the genome still in need of further STS markers for saturation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. An erratum to this article can be found at     

Genome mapping of three major resistance genes to woolly apple aphid (Eriosoma lanigerum Hausm.)

Woolly apple aphid (WAA; Eriosoma lanigerum Hausm.) can be a major economic problem to apple growers in most parts of the world, and resistance breeding provides a sustainable means to control this pest. We report molecular markers for three genes conferring WAA resistance and placing them on two linkage groups (LG) on the genetic map of apple. The Er1 and Er2 genes derived from ‘Northern Spy’ and ‘Robusta 5,’ respectively, are the two major genes that breeders have used to date to improve the resistance of apple rootstocks to this pest. The gene Er3, from ‘Aotea 1’ (an accession classified as Malus sieboldii), is a new major gene for WAA resistance. Genetic markers linked to the Er1 and Er3 genes were identified by screening random amplification of polymorphic deoxyribonucleic acid (DNA; RAPD) markers across DNA bulks from resistant and susceptible plants from populations segregating for these genes. The closest RAPD markers were converted into sequence-characterized amplified region markers and the genome location of these two genes was assigned to LG 08 by aligning the maps around the genes with a reference map of ‘Discovery’ using microsatellite markers. The Er2 gene was located on LG 17 of ‘Robusta 5’ using a genetic map developed in a M.9 × ‘Robusta 5’ progeny. Markers for each of the genes were validated for their usefulness for marker-assisted selection in separate populations. The potential use of the genetic markers for these genes in the breeding of apple cultivars with durable resistance to WAA is discussed.     

High-resolution genetic map of the <Emphasis Type="Italic">Rvi15</Emphasis> (<Emphasis Type="Italic">Vr2</Emphasis>) apple scab resistance locus

The Rvi15 (Vr2) apple scab resistance locus found in the GMAL 2473 accession has been previously mapped to the top of the Linkage Group 2 (LG2) by analyzing 89 progeny plants of a cross between ‘Idared’ and GMAL 2473. A new population of 989 progeny plants, derived from a cross between ‘Golden Delicious’ and GMAL 2473, has been analyzed with the two SSR markers CH02c02a and CH02f06, previously found to be associated with Rvi15 (Vr2), and with two published markers derived from NBS sequences (ARGH17 and ARGH37) estimated to map close to the Rvi15 (Vr2) locus. ARGH17 and ARGH37, were found to be the closest markers to the resistance locus, bracketing it within an interval of 1.5 cM. The SSRs mapped one on each side of Rvi15 (Vr2). CH02f06 mapped at 2.9 cM from ARGH37 while CH02a02a mapped at 1.7 from ARGH17. The position of Rvi15 (Vr2) respect to CH02a02a indicates that Rvi15 (Vr2) and Rvi4 (Vh4), a second apple scab gene mapped on the top of LG2, are two different resistance genes. In order to develop even more tightly linked markers to Rvi15 (Vr2), ARGH17 was used as the starting point for chromosome walking through the Rvi15 (Vr2) homolog region of the cv. ‘Florina’. A single ‘Florina’ BAC clone, 36I17, was sufficient to span the homologous locus in the new population’s recombinant progeny. Sequencing of the 36I17 BAC clone allowed identifying seven putative ORFs, including two showing a TIR-NBS-LRR structure. Ten additional markers could be developed mapping within a 1.8 cM interval around the Rvi15 (Vr2) resistance gene. ARGH17 and GmTNL1 markers, the latter also derived from NBS-LRR resistance gene homolog sequence, are the closest markers to Rvi15 (Vr2) bracketing it within a 0.5 cM interval. The availability of 12 markers within the Rvi15 (Vr2) region, all within a small physical distance (kbp) in ‘Florina’, suggests that cloning of the Rvi15 (Vr2) apple scab resistance gene from GMAL 2473 will be possible.     

QTL analysis for aphid resistance and growth traits in apple

The rosy apple aphid (Dysaphis plantaginea), the leaf-curling aphid (Dysaphis cf. devecta) and the green apple aphid (Aphis pomi) are widespread pest insects that reduce growth of leaves, fruits and shoots in apple (Malus × domestica). Aphid control in apple orchards is generally achieved by insecticides, but alternative management options like growing resistant cultivars are needed for a more sustainable integrated pest management (IPM). A linkage map available for a segregating F₁-cross of the apple cultivars ‘Fiesta’ and ‘Discovery’ was used to investigate the genetic basis of resistance to aphids. Aphid infestation and plant growth characteristics were repeatedly assessed for the same 160 apple genotypes in three different environments and 2 consecutive years. We identified amplified fragment length polymorphism (AFLP) markers linked to quantitative trait loci (QTLs) for resistance to D. plantaginea (‘Fiesta’ linkage group 17, locus 57.7, marker E33M35–0269; heritability: 28.3%), and to D. cf. devecta (‘Fiesta’ linkage group 7, locus 4.5, marker E32M39–0195; heritability: 50.2%). Interactions between aphid species, differences in climatic conditions and the spatial distribution of aphid infestation were identified as possible factors impeding the detection of QTLs. A pedigree analysis of simple sequence repeat (SSR) marker alleles closely associated with the QTL markers revealed the presence of the alleles in other apple cultivars with reported aphid resistance (‘Wagener’, ‘Cox’s Orange Pippin’), highlighting the genetic basis and also the potential for gene pyramiding of aphid resistance in apple. Finally, significant QTLs for shoot length and stem diameter were identified, while there was no relationship between aphid resistance and plant trait QTLs. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Selecting dwarf apple (Malus × domestica Borkh.) trees in vitro: multiple cytokinin tolerance expressed among three strains of ‘McIntosh’ that differ in their growth habit under field conditions

Microcuttings of three strains of ‘McIntosh’ apple that varied in their growth habit under field conditions were tested for their tolerance to three cytokinins (BA, kinetin, and 2iP) and one cytokinin-like compound (TDZ) in vitro. The three strains were ‘McIntosh’ (standard), ‘Macspur’ (intermediate) and ‘Wijcik’ (dwarf). For each cytokinin ‘Wijcik’ was more tolerant of high cytokinin levels than either ‘Macspur‘, which showed an intermediate tolerance, or ‘McIntosh’ which did not tolerate (died) high levels of cytokinins. These results show that ‘Wijcik’ exhibits multiple cytokinin tolerance in vitro. The relationship between growth habit and BA tolerance has been reported earlier. The present study demonstrates that cytokinins can be used to differentiate among growth types in apple. This revised version was published online in June 2006 with corrections to the Cover Date.     

Construction of a dense genetic linkage map for apple rootstocks using SSRs developed from Malus ESTs and Pyrus genomic sequences

Marker-assisted selection (MAS) offers quick and reliable prediction of the phenotypes of seedlings in large populations and thus opens new approaches for selection to breeders of apple (Malus x domestica Borkh.). The development of framework maps enables the discovery of genetic markers linked to desired traits. Although genetic maps have been reported for apple scion cultivars, none has previously been constructed for apple rootstocks. We report the construction of framework genetic maps in a cross between ‘M.9’ (‘Malling 9’) and ‘R.5’ (‘Robusta 5’) apple rootstocks. The maps comprise 224 simple sequence repeat (SSR) markers, 18 sequence-characterised amplified regions, 14 single nucleotide polymorphisms and 42 random amplified polymorphic DNAs. A new set of 47 polymorphic SSRs was developed from apple EST sequences and used for construction of this rootstock map. All 17 linkage groups have been identified and aligned to existing apple genetic maps. The maps span 1,175.7 cM (‘M.9’) and 1,086.7 cM (‘R.5’). To improve the efficiency of mapping markers to this framework map, we developed a bin mapping set. Applications of these new genetic maps include the elucidation of the genetic basis of the dwarfing effect of the apple rootstock ‘M.9’ and the analysis of disease and insect resistance traits such as fire blight (Erwinia amylovora), apple scab (Venturia inaequalis) and woolly apple aphid (Eriosoma lanigerum). Markers for traits mapped in this population will be of direct use to apple breeders for MAS and for identification of causative genes by map-based cloning.     

Refined mapping of the Pierce’s disease resistance locus, PdR1, and Sex on an extended genetic map of Vitis rupestris × V. arizonica

A framework genetic map based on genomic DNA-derived SSR, EST-derived SSR, EST-STS and EST-RFLP markers was developed using 181 genotypes generated from D8909-15 (female) × F8909-17 (male), the ‘9621’ population. Both parents are half siblings with a common female parent, Vitis rupestris ‘A. de Serres’, and different male parents (forms of V. arizonica). A total of 542 markers were tested, and 237 of them were polymorphic for the female and male parents. The female map was developed with 159 mapped markers covering 865.0 cM with an average marker distance of 5.4 cM in 18 linkage groups. The male map was constructed with 158 mapped molecular markers covering 1055.0 cM with an average distance of 6.7 cM in 19 linkage groups. The consensus ‘9621’ map covered 1154.0 cM with 210 mapped molecular markers in 19 linkage groups, with average distance of 5.5 cM. Ninety-four of the 210 markers on the consensus map were new. The ‘Sex’ expression locus segregated as single major gene was mapped to linkage group 2 on the consensus and the male map. PdR1, a major gene for resistance to Pierce’s disease, caused by the bacterium Xylella fastidiosa, was mapped to the linkage group 14 between markers VMCNg3h8 and VVIN64, located 4.3 and 2.7 cM away from PdR1, respectively. Differences in segregation distortion of markers were also compared between parents, and three clusters of skewed markers were observed on linkage groups 6, 7 and 14.     

Leaf pubescence mediates the abundance of non-prey food and the density of the predatory mite Typhlodromus pyri

Plants with leaves having numerous trichomes or domatia frequently harbor greater numbers of phytoseiid mites than do plant with leaves that lack these structures. We tested the hypothesis that this pattern occurs, in part, with Typhlodromus pyri because trichomes increase the capture of pollen or fungal spores that serve as alternative food. Using a common garden orchard, we found that apple varieties with trichome-rich leaves had 2–3 times more pollen and fungal spores compared to varieties with trichome-sparse leaves. We also studied the effects of leaf trichome density and pollen augmentation on T. pyri abundance to test the hypothesis that leaf trichomes mediate pollen and fungal spore capture and retention and thereby influence phytoseiid numbers. Cattail pollen (Typha sp.) was applied weekly to mature ‘McIntosh’ and ‘Red Delicious’ trees grown in an orchard and, in a separate experiment, to potted trees of the same varieties. ‘McIntosh’ trees have leaves with many trichomes whereas leaves on the ‘Red Delicious’ trees have roughly half as many trichomes. With both field-grown and potted trees, adding cattail pollen to ‘Red Delicious’ trees increased T. pyri numbers compared to ‘Red Delicious’ trees without pollen augmentation. In contrast, cattail pollen augmentation had no effect on T. pyri populations on ‘McIntosh’ trees. Augmentation with cattail pollen most likely supplemented a lower supply of naturally available alternative food on ‘Red Delicous’ leaves and thereby enhanced predator abundance. These studies indicate that larger populations of T. pyri on pubescent plants are due, in part, to the increased capture and retention of pollen and fungal spores that serve as alternative foods. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular mapping of leaf rust resistance gene <Emphasis Type="Italic">Rph14</Emphasis> in <Emphasis Type="Italic">Hordeum vulgare</Emphasis>

An incompletely dominant gene conferring resistance to Puccinia hordei, Rph14, identified previously in an accession of Hordeum vulgare, confers resistance to all known pathotypes of P. hordei in Australia. Knowledge of the chromosomal location of Rph14 and the identification of DNA markers closely linked to it will facilitate combining it with other important leaf rust resistance genes to achieve long lasting resistance. The inheritance of Rph14 was confirmed using 146 and 106 F₃ lines derived from the crosses ‘Baudin’/‘PI 584760’ (Rph14) and ‘Ricardo’/‘PI 584760’ (Rph14), respectively. Bulk segregant analysis on DNA from the parental genotypes and resistant and susceptible DNA bulks using DArT markers located Rph14 to the short arm of chromosome 2H. DArT marker bPb-1664 was identified as having the closest genetic association with Rph14. PCR based marker analysis identified a single SSR marker, Bmag692, linked closely to Rph14 at a map distance of 2.1 and 3.8 cm in the ‘Baudin’/‘PI 584760’and ‘Ricardo’/‘PI 584760’ populations, respectively.     

Microsatellite diversity in tetraploid <Emphasis Type="Italic">Gossypium</Emphasis> germplasm: assembling a highly informative genotyping set of cotton SSRs

A series of 320 mapped simple sequence repeats (SSRs) have been used to screen the allelic diversity of tetraploid Gossypium species. Fourty-seven genotypes were analyzed representing (i) the wide spectrum of diversity of the cultivated pool and of the primitive landraces of species G. hirsutum (‘marie-galante’, ‘punctatum’, ‘richmondi’, ‘morrilli’, ‘palmeri’, and ‘latifolium’, and ‘yucatanense’), and (ii) species G. barbadense, G. darwinii and G. tomentosum. The polymorphism of 201 SSR loci revealed 1128 allelic variants ranging from 3 to 17 per locus. Neighbor-joining (NJ) method based on genetic dissimilarities produced groupings consistent with the assignments of accessions both at species and at race level. Our data confirmed the proximity of the Galapagos endemic species G. darwinii to species G. barbadense. Within species G. hirsutum, and as compared to the other 6 races, race yucatanense appeared as the most distant from cultivated genotypes. Race yucatanense also exhibited the highest number of unique alleles. The important informative heterogeneity of the 201 SSR loci was exploited to select the most polymorphic ones that were assembled into three series of genome-wide (i.e. each homoeologous AD chromosome pair being equally represented) and mutliplexable (× 3) SSRs. Using one of these ‘genotyping set’, consisting of 39 SSRs (one 3-plex for each of the 13 AD chromosomes pairs) or 45 loci, we were able to assess the relationships between accessions and the topology in the genetic diversity sampled. Such genotyping set of highly informative SSR markers assembled in PCR-multiplex, while increasing genotyping throughput, will be applicable for molecular genetic diversity studies of large germplasm collections. Electronic Supplementary Material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

A genetic linkage map for an apricot (<Emphasis Type="Italic">Prunus armeniaca</Emphasis> L.) BC<Subscript>1</Subscript> population mapping <Emphasis Type="Italic">plum pox virus</Emphasis> resistance

Plum pox virus (sharka; PPV) can cause severe crop loss in economically important Prunus species such as peach, plum, apricot, and cherry. Of these species, certain apricot cultivars (‘Stark Early Orange’, ‘Goldrich’, ‘Harlayne’) display significant levels of resistance to the disease and are the genetic substrate for studies of several xlaboratories working cooperatively to genetically characterize and mark the resistance locus or loci for marker-assisted breeding. The goals of the work presented in this communication are the characterization of the genetics of PPV resistance in ‘Stark Early Orange’ and the development of co-dominant molecular markers for marker-assisted selection (MAS) in PPV resistance breeding. We present the first genetic linkage map for an apricot backcross population of ‘Stark Early Orange’ and the susceptible cultivar ‘Vestar’ that segregates for resistance to PPV. This map is comprised of 357 loci (330 amplified fragment length polymorphisms (AFLPs), 26 simple sequence repeats (SSRs), and 1 morphological marker for PPV resistance) assigned to eight linkage groups. Twenty-two of the mapped SSRs are shared in common with genetic reference map for Prunus (T × E; Joobeur et al. 1998) and anchor our apricot map to the general Prunus map. A PPV resistance locus was mapped in linkage group 1 and four AFLP markers segregating with the PPV resistance trait, identified through bulk segregant analysis, facilitated the development of SSRs in this region. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Lalli, D.A. and Salava, J. contributed equally to this work.     

Rust mite resistance in apple assessed by quantitative trait loci analysis

The aim of this study was to assess the genetic basis of rust mite (Aculus schlechtendali) resistance in apple (Malus × domestica). A. schlechtendali infestation of apple trees has increased as a consequence of reduced side effects of modern fungicides on rust mites. An analysis of quantitative trait loci (QTLs) was carried out using linkage map data available for F₁ progeny plants of the cultivars ‘Fiesta’ × ‘Discovery’. Apple trees representing 160 different genotypes were surveyed for rust mite infestation, each at three different sites in two consecutive years. The distribution of rust mites on the individual apple genotypes was aggregated and significantly affected by apple genotype and site. We identified two QTLs for A. schlechtendali resistance on linkage group 7 of ‘Fiesta’. The AFLP marker E35M42-0146 (20.2 cM) and the RAPD marker AE10-400 (45.8 cM) were closest positioned to the QTLs and explained between 11.0% and 16.6% of the phenotypic variability. Additionally, putative QTLs on the ‘Discovery’ chromosomes 4, 5 and 8 were detected. The SSR marker Hi03a10 identified to be associated to one of the QTLs (AFLP marker E35M42-0146) was traced back in the ‘Fiesta’ pedigree to the apple cultivar ‘Wagener’. This marker may facilitate the breeding of resistant apple cultivars by marker assisted selection. Furthermore, the genetic background of rust mite resistance in existing cultivars can be evaluated by testing them for the identified SSR marker. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

QTL mapping of aroma compounds analysed by headspace solid-phase microextraction gas chromatography in the apple progeny ‘Discovery’ × ‘Prima’

Improving fruit quality of apple varieties is an important but complex breeding goal. Flavour is among the key factors of apple fruit quality but in spite of the analytical and biochemical knowledge about volatiles little is known about the genetic and molecular bases of apple aroma. The aim of this study was to use a saturated molecular linkage map of apple to identify QTLs for aroma compounds such as alcohols, esters and terpenes, but also for a number of unidentified volatile compounds (non-targeted analysis approach). Two parental genetic maps were constructed for the apple cultivars ‘Discovery’ and ‘Prima’ by using mainly AFLP and SSR markers. ‘Discovery’ and ‘Prima’ showed very different volatile patterns, and ‘Discovery’ mostly had the higher volatile concentrations in comparison with the Vf-scab resistant ‘Prima’ which has its origin in the small-fruited apple species Malus floribunda. About 50 putative QTLs for a total of 27 different apple fruit volatiles were detected through interval mapping by using genotypic data of 150 F₁ individuals of the mapping population ‘C3’ together with phenotypic data obtained by head-space solid phase microextraction gas chromatography. QTLs for volatile compounds putatively involved in apple aroma were found on 12 out of the 17 apple chromosomes, but they were not evenly dispersed. QTLs were mainly clustered on linkage groups LG 2, 3 and 9. In a first attempt, a LOX (lipoxygenase) candidate gene, putatively involved in volatile metabolism, was mapped on LG 9, genetically associated with a cluster of QTLs for ester-type volatiles. Implications for aroma breeding in apple are discussed.     

Identification of a major QTL for time of initial vegetative budbreak in apple (<Emphasis Type="Italic">Malus</Emphasis> x <Emphasis Type="Italic">domestica</Emphasis> Borkh.)

In the Western Cape region of South Africa, dormancy release and the onset of growth does not occur normally in apple (Malus x domestica Borkh.) trees during spring due to the mild winter conditions experienced and fluctuations in temperatures experienced during and between winters. In this region, the application of chemicals to induce the release of dormancy forms part of standard orchard management. Increasing awareness of the environmental impact of chemical sprays and global warming has led to the demand for new apple cultivars better adapted to local climatic conditions. We report the construction of framework genetic maps in two F1 crosses using the low chilling cultivar ‘Anna’ as common male parent and the higher chill requiring cultivars ‘Golden Delicious’ and ‘Sharpe’s Early’ as female parents. The maps were constructed using 320 simple sequence repeats, including 116 new markers developed from expressed sequence tags. These maps were used to identify quantitative trait loci (QTL) for time of initial vegetative budbreak (IVB), a dormancy related characteristic. Time of IVB was assessed four times over a 6-year period in ‘Golden Delicious’ x ‘Anna’ seedlings kept in seedling bags under shade in the nursery. The trait was assessed for 3 years on adult full-sib trees derived from a cross between ‘Sharpe’s Early’ and ‘Anna’ as well as for 3 years on replicates of these seedlings obtained by clonal propagation onto rootstocks. A single major QTL for time of IVB was identified on linkage group (LG) 9. This QTL remained consistent in different genetic backgrounds and at different developmental stages. The QTL may co-localize with a QTL for leaf break identified on LG 3 by Conner et al. (1998), a LG that was, after the implementation of transferable microsatellite markers, shown to be homologous to the LG now known to be LG 9 (Kenis and Keulemans 2004). These results contribute towards a better understanding regarding the genetic control of IVB in apple and will also be used to elucidate the genetic basis of other dormancy related traits such as time of initial reproductive budbreak and number of vegetative and reproductive budbreak.     

Genetic and physical characterisation of the locus controlling columnar habit in apple (Malus × domestica Borkh.)

A better understanding of the genetic control of tree architecture would potentially allow improved tailoring of newly bred apple cultivars in terms of field management aspects, such as planting density, pruning, pest control and disease protection. It would also have an indirect impact on yield and fruit quality. The Columnar (Co) locus strongly suppresses lateral branch elongation and is the most important genetic locus influencing tree architecture in apple. Co has previously been mapped on apple linkage group (LG) 10. In order to obtain fine mapping of Co, both genetically and physically, we have phenotypically analysed and screened three adult segregating experimental populations, with a total of 301 F₁ plants, and one substantial 3-year old population of 1,250 F₁ plants with newly developed simple sequence repeat (SSR) markers, based on the ‘Golden delicious’ apple genome sequence now available. Co was found to co-segregate with SSR marker Co04R12 and was confined in a region of 0.56 cM between SSR markers Co04R11 and Co04R13, corresponding to 393 kb on the ‘Golden delicious’ genome sequence. In this region, 36 genes were predicted, including at least seven sequences potentially belonging to genes that could be considered candidates for involvement in control of shoot development. Our results provide highly reliable, virtually co-segregating markers that will facilitate apple breeding aimed at modifications of the tree habit and lay the foundations for the cloning of Co.     

Identification and assessment of genetic relationships in three <Emphasis Type="Italic">Chlorophytum</Emphasis> species and two high yielding genotypes of <Emphasis Type="Italic">C. borivilianum</Emphasis> through RAPD markers

Conservation of identified germplasm is an important component for efficient and effective management of plant genetic resources. Since Chlorophytum species are important medicinal plants, studies were carried out for identification and establish genetic relationships in three species of Chlorophytum and two high yielding genotypes of Chlorophtum borivilianum using RAPD markers. Out of one hundred primers tested, 47 decamers amplified a total of 454 distinct bands ranging from 0.25–3.0 kbp to identify and to evaluate genetic relationships between and among three species of Chlorophytum and two genotypes of Chlorophtum borivilianum. The cluster analysis indicated that three species of Chlorophytum and two genotypes (NRCCB-1 and NRCCB-2) of C. borivilianum formed two major clusters. The first major cluster constituted C. arundinaceum and C. tuberosum, and the second major cluster composed of two subclusters; the first subcluster represented NRCB-1 and NRCB-2 where as the second subcluster represented C. borivilianum. Thus, the RAPD markers have the potential for identification and characterization of genetic relatedness among the species and genotypes. C. borivilianum along with two genotypes also showed similar banding patterns which could be chosen as candidate markers for differentiating the other two species such as C. arundinaceum and C. tuberosum. This would helpful for breeding programmes and provides an important input in conservation biology.     

Long-term study of somatic embryogenesis from anthers and ovaries of 12 grapevine (<Emphasis Type="Italic">Vitis</Emphasis> sp.) genotypes

Summary Anthers and ovaries of six grapevine cultivars (three Vitis vinifera L., two V × Labruscana L. H. Bailey, and one complex hybrid) were extracted from flower buds over 2 yr and cultured on three media reported to promote somatic embryogenesis in Vitis tissues. The highest percent embryogenesis from the hybrid ‘Chancellor’ and V. vinifera ‘Chardonnay’, ‘Merlot’, and ‘Pinot Noir’ occurred on medium C [Nitsch and Nitsch, 1969, basal medium with 3.0% (w/v) sucrose, 0.01% (w/v) inositol. 0.3% (w/v) Phytagel, 2.5 μM 2.4-dichlorophenoxyacetic acid, 2.5μM β-naphthoxyacetic acid, 5.0μM N-(2-chloro-4-pyridyl)-N′-phenylurea, and 0.05% (w/v) glutamine]. Regardless of the media, the labrusca cultivars ‘Concord’ and ‘Niagara’ produced soft non-embryogenic callus that was sometimes mixed with well-developed somatic embryos. Nine vinifera genotypes were further tested for several different years on medium C. Embryogenic cultures suitable for transformation were obtained from all genotypes in more than 1 yr. The average percent embryogenesis from ovaries was 7-fold higher than from anthers. There was significant annual variation in percent embryogenesis, demonstrating the need for media comparisons to be replicated for more than one season. Suspension cultures suitable for use in genetic transformation were initiated from ‘Chardonnay’, ‘Merlot,’ and ‘Pinot Noir’ pro-embryogenic masses. ‘Chardonnay’ suspension cultures plated and grown under conditions developed for recovery of plants after biolistic transformation yielded approximately 500 non-transformed embryos per plate after 4 mo. of culture, with 68.6% of the embryos converting to plants. This is the first reported protocol for embryogenesis from ‘Concord,’ ‘Cabernet Franc,’ and ‘Pinot Noir’ grapevines.     

Linkage maps of the apple ( Malus × domestica Borkh.) cvs ‘Ralls Janet’ and ‘Delicious’ include newly developed EST markers

Two apple genetic linkage maps were constructed using amplified fragment length polymorphisms (AFLPs), simple sequence repeats (SSRs), random amplified polymorphic DNAs (RAPDs), and expressed sequence tag (EST)-derived markers in combination with a pseudo-testcross mapping strategy in which the cultivars ‘Ralls Janet’ and ‘Delicious’ were used as the respective seed parents. Mitsubakaido (Malus sieboldii) was used as the pollen parent for each of the segregating F₁ populations. Expressed sequence tag data were obtained from the random sequencing of cDNA libraries constructed from in vitro cultured shoots and maturing fruits of cv ‘Fuji’, which is the offspring of a cross between ‘Ralls Janet’ and ‘Delicious’. In addition, a number of published gene sequences were used to develop markers for mapping. The ‘Ralls Janet’ map consisted of 346 markers (178 AFLPs, 95 RAPDs, 54 SSRs, 18 ESTs, and the S locus) in 17 linkage groups, with a total length of 1082 cM, while that of ‘Delicious’ comprised 300 markers (120 AFLPs, 81 RAPDs, 64 SSRs, 32 ESTs, and the S, Rf, and MdACS-1 loci) on 17 linkage groups spanning 1031 cM. These maps are amenable to comparisons with previously published maps of ‘Fiesta’ and ‘Discovery’ (Liebhard et al., Mol Breed 10:217–241, 2002; Liebhard et al., Theor Appl Genet 106:1497–1508, 2003a) because several of the SSRs (one to three markers per linkage group) were used in all of the maps. Distorted marker segregation was observed in three and two regions of the ‘Ralls Janet’ and ‘Delicious’ maps, respectively. These regions were localized in different parts of the genome from those in previously reported apple linkage maps. This marker distortion may be dependent on the combinations of cultivars used for map construction.