Transcript Profiles of Auxin Efflux Carrier and IAA-Amido Synthetase Genes Suggest the Role of Auxin on Apple (<i>Malus</i>×<i>domestica</i>) Fruit Maturation Patterns

Auxin has been suggested to play an essential role in regulating apple fruit maturation and ripening, though the molecular function of auxin and its interaction with ethylene during apple fruit development are largely unknown. To understand the function of auxin during apple fruit maturation and ripening, auxin efflux carrier and IAA-amido synthetase encoding genes were identified from the apple genome based on the results of previous microarray analysis. The expression patterns of these genes were analyzed using qRT-PCR during 10 - 12 weeks of fruit maturation for two apple cultivars: “Golden Delicious” (GD) and “Cripps Pink” (CP), which have the distinct patterns of maturation progression. Our results showed that the expressions of auxin efflux carrier and IAA-amido synthetase genes have a correlation with the timing of ethylene biosynthesis pathway activation in both cultivars. The earlier and stronger expression of MdGH3.102 and MdAECFP1 in the fruit of GD, a mid-season cultivar, correlates with the earlier activation of a pre-climacteric ethylene biosynthesis gene of MdACS3, compared with that in CP, a late-ripening apple cultivar. Results of exogenous IAA treatment indicated that the expression patterns of the genes were regulated in a fruit maturity dependent manner. Our results suggested that the dynamics of the auxin level in apple fruit cortex could be one of the key factors influencing the timing of ethylene biosynthesis pathway activation and consequently contributed to the control of the apple maturation progression.

Cost and accuracy of advanced breeding trial designs in apple

Trialing advanced candidates in tree fruit crops is expensive due to the long-term nature of the planting and labor-intensive evaluations required to make selection decisions.How closely the trait evaluations approximate the true trait value needs balancing with the cost of the program.Designs of field trials of advanced apple candidates in which reduced number of locations,the number of years and the number of harvests per year were modeled to investigate the effect on the cost and accuracy in an operational breeding program.The aim was to find designs that would allow evaluation of the most additional candidates while sacrificing the least accuracy.Critical percentage difference,response to selection,and correlated response were used to examine changes in accuracy of trait evaluations.For the quality traits evaluated,accuracy and response to selection were not substantially reduced for most trial designs.Risk management influences the decision to change trial design,and some designs had greater risk associated with them.Balancing cost and accuracy with risk yields valuable insight into advanced breeding trial design.The methods outlined in this analysis would be well suited to other horticultural crop breeding programs.

Excised Leaf Bioassay: Phenotypic Expression of Natural Resistance in Apple against the Obliquebanded Leafroller

Different approaches were assessed in the development of a bioassay method that would provide data necessary to evaluate resistance of apple genotypes to the obliquebanded leafroller (OBLR) Choristoneura rosaceana (Harris). A leaf disc method used to evaluate the impact of pesticides on leafrollers resulted in high levels of leaf-abandonment of first and second instar larvae. Inserting leaf petioles into water soaked Oasis foam resulted in a significant reduction in overall leaf weight and diminished the appearance of leaf quality. When leaf petioles were inserted into water-filled Eppendorf vials, leaf weight increased and overall leaf quality appeared to be good. We opted to adopt this latter whole-leaf bioassay method, which though very time consuming, provided a robust assessment of OBLR life history parameters against different apple genotypes. Across all apple genotypes evaluated, male larvae developed faster than females to pupation as well as to adulthood, while females developed faster as pupae and were heavier than male pupae. OBLR larvae reared on leaves from different apple genotypes displayed significant variability in development time, pupal weight, larval survivorship, and number of offspring produced. We utilized three indices to characterize host acceptance, sub-lethal effects, and lethal effects of OBLR to apple genotypes. Our results indicated that ‘Lady’, ‘Viking’, and ‘Northern Spy’ show some of the highest levels of resistance against OBLR, while ‘Granny Smith’ was quite susceptible to OBLR and could be used in future studies identifying apple genotypes with relative resistance to OBLR.

嘎拉苹果高温处理与果实日灼的关系

高温处理对诱导果实增强对日灼的抗性有一定的作用 ,可降低日灼率。苹果果实在 4 5℃下处理 2h ,在3d后将处理果和对照果同时暴露在阳光下 ,结果发现 :热处理能够在一定程度上增强果实对日灼的抗性。在 4 5℃下处理 2、4和 6h后立即取样或室温下放置 2 4h后取样 ,对热激蛋白的分析表明 ,大分子量热激蛋白量变化不大 ,而小分子量热激蛋白可能在诱导果实抗热性方面起重要作用。随着处理时间延长 ,在一定时间范围内 ,热激蛋白抗热性水平增加。经测定 ,树冠外围充分曝光果和树冠内膛遮荫果对比 ,二者热激蛋白含量有显著差异 ,这可能是遮荫果对日灼更为敏感的原因。

Fire blight QTL analysis in a multi-family apple population identifies a reduced-susceptibility allele in ‘Honeycrisp’

Breeding apple cultivars with resistance offers a potential solution to fire blight,a damaging bacterial disease caused by Erwinia amylovora.Most resistance alleles at quantitative trait loci(QTLs)were previously characterized in diverse Malus germplasm with poor fruit quality,which reduces breeding utility.This study utilized a pedigree-based QTL analysis approach to elucidate the genetic basis of resistance/susceptibility to fire blight from multiple genetic sources in germplasm relevant to U.S.apple breeding programs.Twenty-seven important breeding parents(IBPs)were represented by 314 offspring from 32 full-sib families,with‘Honeycrisp’being the most highly represented IBP.Analyzing resistance/susceptibility data from a two-year replicated field inoculation study and previously curated genome-wide single nucleotide polymorphism data,QTLs were consistently mapped on chromosomes(Chrs.)6,7,and 15.These QTLs together explained~28% of phenotypic variation.The Chr.6 and Chr.15 QTLs colocalized with previously reported QTLs,while the Chr.7 QTL is possibly novel.‘Honeycrisp’inherited a rare reduced-susceptibility allele at the Chr.6 QTL from its grandparent‘Frostbite’.The highly resistant IBP‘Enterprise’had at least one putative reduced-susceptibility allele at all three QTLs.In general,lower susceptibility was observed for individuals with higher numbers of reduced-susceptibility alleles across QTLs.This study highlighted QTL mapping and allele characterization of resistance/susceptibility to fire blight in complex pedigree-connected apple breeding germplasm.Knowledge gained will enable more informed parental selection and development of trait-predictive DNA tests for pyramiding favorable alleles and selection of superior apple cultivars with resistance to fire blight.

Modeling of genetic gain for single traits from marker-assisted seedling selection in clonally propagated crops

Seedling selection identifies superior seedlings as candidate cultivars based on predicted genetic potential for traits of interest.Traditionally,genetic potential is determined by phenotypic evaluation.With the availability of DNA tests for some agronomically important traits,breeders have the opportunity to include DNA information in their seedling selection operations—known as marker-assisted seedling selection.A major challenge in deploying marker-assisted seedling selection in clonally propagated crops is a lack of knowledge in genetic gain achievable from alternative strategies.Existing models based on additive effects considering seed-propagated crops are not directly relevant for seedling selection of clonally propagated crops,as clonal propagation captures all genetic effects,not just additive.This study modeled genetic gain from traditional and various marker-based seedling selection strategies on a single trait basis through analytical derivation and stochastic simulation,based on a generalized seedling selection scheme of clonally propagated crops.Various trait-test scenarios with a range of broad-sense heritability and proportion of genotypic variance explained by DNA markers were simulated for two populations with different segregation patterns.Both derived and simulated results indicated that marker-based strategies tended to achieve higher genetic gain than phenotypic seedling selection for a trait where the proportion of genotypic variance explained by marker information was greater than the broad-sense heritability.Results from this study provides guidance in optimizing genetic gain from seedling selection for single traits where DNA tests providing marker information are available.

Genetic analysis of stilbenoid profiles in grapevine stems reveals a major mQTL hotspot on chromosome 18 associated with disease-resistance motifs

Grapevine(Vitis spp.)contains a wealth of phytochemicals that have received considerable attention due to healthpromoting properties and biological activities as phytoalexins.To date,the genetic basis of the quantitative variations for these potentially beneficial compounds has been limited.Here,metabolic quantitative trait locus(mQTL)mapping was conducted using grapevine stems of a segregating F2 population.Metabolic profiling of grapevine stems was performed using liquid chromatography–high-resolution mass spectrometry(LC-HRMS),resulting in the detection of 1317 ions/features.In total,19 of these features matched with literature-reported stilbenoid masses and were genetically mapped using a 1449-SNP linkage map and R/qtl software,resulting in the identification of four mQTLs.Two large-effect mQTLs that corresponded to a stilbenoid dimer and a trimer were mapped on chromosome 18,accounting for phenotypic variances of 29.0%and 38.4%.Functional annotations of these large-effect mQTLs on the VitisNet network database revealed a major hotspot of disease-resistance motifs on chromosome 18.This 2.8-Mbp region contains 48 genes with R-gene motifs,including variants of TIR,NBS,and LRR,that might potentially confer resistance to powdery mildew,downy mildew,or other pathogens.The locus also encompasses genes associated with flavonoid and biosynthetic pathways that are likely involved in the production of secondary metabolites,including phytoalexins.In addition,haplotype dosage effects of the five mQTLs further characterized the genomic regions for differential production of stilbenoids that can be applied in resistance breeding through manipulation of stilbenoid production in planta.