Ploidy variation in subsection and its implications for conservation.

Polyploidy, which is common in plants, can confound taxon recognition and hence conservation assessments. In the taxonomically complex genus , 25 % of the over 1,300 taxa are considered under threat and 27 % Near Threatened or Data Deficient, with their taxonomy needing to be resolved urgently. Although ploidy levels of taxa range from diploid (2) to dodecaploid (12) according to previous reports, the extent of polyploidy across the genus has not been examined.

Molecular characterization of intergeneric hybrids between and .

Apple () and pear () are economically important fruit crops well known for their unique textures, flavours, and nutritional qualities. Both genera are characterised by a distinct pattern of secondary metabolites, which directly affect not only resistance to certain diseases, but also have significant impacts on the flavour and nutritional value of the fruit. The identical chromosome numbers, similar genome size, and their recent divergence date, together with DNA markers have shown that apple and pear genomes are highly co-linear.

QTL Mapping for Resistance to Cankers Induced by pv. (Psa) in a Tetraploid Kiwifruit Population.

Polyploidy is a key driver of significant evolutionary changes in plant species. The genus (kiwifruit) exhibits multiple ploidy levels, which contribute to novel fruit traits, high yields and resistance to the canker-causing dieback disease incited by pv. (Psa) biovar 3.

Pseudo-chromosome-length genome assembly of a double haploid "Bartlett" pear (Pyrus communis L.).

Background: We report an improved assembly and scaffolding of the European pear (Pyrus communis L.) genome (referred to as BartlettDHv2.0), obtained using a combination of Pacific Biosciences RSII long-read sequencing, Bionano optical mapping, chromatin interaction capture (Hi-C), and genetic mapping.

Mapping of fire blight resistance in Malus ×robusta 5 flowers following artificial inoculation.

Background: Although the most common path of infection for fire blight, a severe bacterial disease on apple, is via host plant flowers, quantitative trait loci (QTLs) for fire blight resistance to date have exclusively been mapped following shoot inoculation. It is not known whether the same mechanism underlies flower and shoot resistance.

Results: We report the detection of a fire blight resistance QTL following independent artificial inoculation of flowers and shoots on two F1 segregating populations derived from crossing resistant Malus ×robusta 5 (Mr5) with susceptible 'Idared' and 'Royal Gala' in experimental orchards in Germany and New Zealand, respectively.

Multiple quantitative trait loci contribute to resistance to bacterial canker incited by pv. in kiwifruit ().

pv. (Psa) biovar 3, a virulent, canker-inducing pathogen is an economic threat to the kiwifruit ( spp.) industry worldwide.

Comparative population genomics identified genomic regions and candidate genes associated with fruit domestication traits in peach.

Crop evolution is a long-term process involving selection by natural evolutionary forces and anthropogenic influences; however, the genetic mechanisms underlying the domestication and improvement of fruit crops have not been well studied to date. Here, we performed a population structure analysis in peach (Prunus persica) based on the genome-wide resequencing of 418 accessions and confirmed the presence of an obvious domestication event during evolution. We identified 132 and 106 selective sweeps associated with domestication and improvement, respectively.

Validation of SNP markers for fruit quality and disease resistance loci in apple ( × Borkh.) using the OpenArray® platform.

Genome mapping has promised much to tree fruit breeding during the last 10 years. Nevertheless, one of the greatest challenges remaining to tree fruit geneticists is the translation of trait loci and whole genome sequences into diagnostic genetic markers that are efficient and cost-effective for use by breeders, who must select genetically optimal parents and subsequently select genetically superior individuals among their progeny. To take this translational step, we designed the apple International RosBREED SNP Consortium OpenArray v1.

A manually annotated Actinidia chinensis var. chinensis (kiwifruit) genome highlights the challenges associated with draft genomes and gene prediction in plants.

Background: Most published genome sequences are drafts, and most are dominated by computational gene prediction. Draft genomes typically incorporate considerable sequence data that are not assigned to chromosomes, and predicted genes without quality confidence measures. The current Actinidia chinensis (kiwifruit) 'Hongyang' draft genome has 164 Mb of sequences unassigned to pseudo-chromosomes, and omissions have been identified in the gene models.

Genome mapping of postzygotic hybrid necrosis in an interspecific pear population.

Deleterious epistatic interactions in plant inter- and intraspecific hybrids can cause a phenomenon known as hybrid necrosis, characterized by a typical seedling phenotype whose main distinguishing features are dwarfism, tissue necrosis and in some cases lethality. Identification of the chromosome regions associated with this type of incompatibility is important not only to increase our understanding of the evolutionary diversification that led to speciation but also for breeding purposes. Development of molecular markers linked to the lethal genes will allow breeders to avoid incompatible inbred combinations that could affect the expression of important agronomic tratis co-segregating with these genes.

Two quantitative trait loci, Dw1 and Dw2, are primarily responsible for rootstock-induced dwarfing in apple.

The apple dwarfing rootstock 'Malling9' ('M9') has been used worldwide both to reduce scion vigour and as a genetic source for breeding new rootstocks. Progeny of 'M9' segregate for rootstock-induced dwarfing of the scion, indicating that this trait is controlled by one or more genetic factors. A quantitative trait locus (QTL) analysis of a rootstock population derived from the cross between 'M9' × 'Robusta5' (non-dwarfing) and grafted with 'Braeburn' scions identified a major QTL (Dw1) on linkage group (LG) 5, which exhibits a significant influence on dwarfing of the scion.

Genetic control of pear rootstock-induced dwarfing and precocity is linked to a chromosomal region syntenic to the apple Dw1 loci.

Background: The vigour and precocity of trees highly influences their efficiency in commercial production. In apple, dwarfing rootstocks allow high-density plantings while their precocious flowering enables earlier fruit production. Currently, there is a lack of pear (Pyrus communis L.

A microRNA allele that emerged prior to apple domestication may underlie fruit size evolution.

The molecular genetic mechanisms underlying fruit size remain poorly understood in perennial crops, despite size being an important agronomic trait. Here we show that the expression level of a microRNA gene (miRNA172) influences fruit size in apple. A transposon insertional allele of miRNA172 showing reduced expression associates with large fruit in an apple breeding population, whereas over-expression of miRNA172 in transgenic apple significantly reduces fruit size.

Scab resistance in 'Geneva' apple is conditioned by a resistance gene cluster with complex genetic control.

Apple scab, caused by the fungal pathogen Venturia inaequalis, is one of the most severe diseases of apple worldwide. It is the most studied plant-pathogen interaction involving a woody species using modern genetic, genomic, proteomic and bioinformatic approaches in both species. Although 'Geneva' apple was recognized long ago as a potential source of resistance to scab, this resistance has not been characterized previously.

Genetic, metabolite and developmental determinism of fruit friction discolouration in pear.

Background: The unattractive appearance of the surface of pear fruit caused by the postharvest disorder friction discolouration (FD) is responsible for significant consumer dissatisfaction in markets, leading to lower returns to growers. Developing an understanding of the genetic control of FD is essential to enable the full application of genomics-informed breeding for the development of new pear cultivars. Biochemical constituents [phenolic compounds and ascorbic acid (AsA)], polyphenol oxidase (PPO) activity, as well as skin anatomy, have been proposed to play important roles in FD susceptibility in studies on a limited number of cultivars.

The draft genome sequence of European pear (Pyrus communis L. 'Bartlett').

We present a draft assembly of the genome of European pear (Pyrus communis) 'Bartlett'. Our assembly was developed employing second generation sequencing technology (Roche 454), from single-end, 2 kb, and 7 kb insert paired-end reads using Newbler (version 2.7).

The AAT1 locus is critical for the biosynthesis of esters contributing to 'ripe apple' flavour in 'Royal Gala' and 'Granny Smith' apples.

The 'fruity' attributes of ripe apples (Malus × domestica) arise from our perception of a combination of volatile ester compounds. Phenotypic variability in ester production was investigated using a segregating population from a 'Royal Gala' (RG; high ester production) × 'Granny Smith' (GS; low ester production) cross, as well as in transgenic RG plants in which expression of the alcohol acyl transferase 1 (AAT1) gene was reduced. In the RG × GS population, 46 quantitative trait loci (QTLs) for the production of esters and alcohols were identified on 15 linkage groups (LGs).

Genetic and environmental control of fruit maturation, dry matter and firmness in apple (Malus × domestica Borkh.).

For any given genotype, the environment in which an apple is grown can influence the properties of the fruit considerably. While there has been extensive research on the mechanism of the genetic control of fruit quality traits, less effort has been made to investigate the way that these genetic mechanisms interact with the environment. To address this issue, we employed a large 'Royal Gala' × 'Braeburn' population of 572 seedlings replicated over sites in three climatically diverse apple-growing regions in New Zealand.

Breeding better cultivars, faster: applications of new technologies for the rapid deployment of superior horticultural tree crops.

Woody perennial plants, including trees that produce fruits and nuts of horticultural value, typically have long breeding cycles, and development and introduction of improved cultivars by plant breeders may require many breeding cycles and dozens of years. However, recent advances in biotechnologies and genomics have the potential to accelerate cultivar development greatly in all crops. This mini-review summarizes approaches to reduce the number and the duration of breeding cycles for horticultural tree crops, and outlines the challenges that remain to implement these into efficient breeding pipelines.

Identification of Pyrus single nucleotide polymorphisms (SNPs) and evaluation for genetic mapping in European pear and interspecific Pyrus hybrids.

We have used new generation sequencing (NGS) technologies to identify single nucleotide polymorphism (SNP) markers from three European pear (Pyrus communis L.) cultivars and subsequently developed a subset of 1096 pear SNPs into high throughput markers by combining them with the set of 7692 apple SNPs on the IRSC apple Infinium® II 8K array. We then evaluated this apple and pear Infinium® II 9K SNP array for large-scale genotyping in pear across several species, using both pear and apple SNPs.

An ancient duplication of apple MYB transcription factors is responsible for novel red fruit-flesh phenotypes.

Anthocyanin accumulation is coordinated in plants by a number of conserved transcription factors. In apple (Malus × domestica), an R2R3 MYB transcription factor has been shown to control fruit flesh and foliage anthocyanin pigmentation (MYB10) and fruit skin color (MYB1). However, the pattern of expression and allelic variation at these loci does not explain all anthocyanin-related apple phenotypes.

Putative resistance gene markers associated with quantitative trait loci for fire blight resistance in Malus 'Robusta 5' accessions.

Background: Breeding of fire blight resistant scions and rootstocks is a goal of several international apple breeding programs, as options are limited for management of this destructive disease caused by the bacterial pathogen Erwinia amylovora. A broad, large-effect quantitative trait locus (QTL) for fire blight resistance has been reported on linkage group 3 of Malus 'Robusta 5'. In this study we identified markers derived from putative fire blight resistance genes associated with the QTL by integrating further genetic mapping studies with bioinformatics analysis of transcript profiling data and genome sequence databases.

Genome-wide SNP detection, validation, and development of an 8K SNP array for apple.

As high-throughput genetic marker screening systems are essential for a range of genetics studies and plant breeding applications, the International RosBREED SNP Consortium (IRSC) has utilized the Illumina Infinium® II system to develop a medium- to high-throughput SNP screening tool for genome-wide evaluation of allelic variation in apple (Malus×domestica) breeding germplasm. For genome-wide SNP discovery, 27 apple cultivars were chosen to represent worldwide breeding germplasm and re-sequenced at low coverage with the Illumina Genome Analyzer II. Following alignment of these sequences to the whole genome sequence of 'Golden Delicious', SNPs were identified using SoapSNP.