Seed Germination Traits of Loquat (Eriobotrya japonica Lindl.) as Affected by Various Pre-Sowing Treatments (Cutting of Cotyledons, Removal of Perisperm, Moist Chilling and/or Exogenous Application of Gibberellin)

The purpose of this study was to investigate the effects of various presowing treatments on the germinability(final germination percentage)and germination rate of loquat seeds in order to increase seedling production in nurseries(applied research)as well as provide answers for important physiological issues related to loquat seeds and their seed coat(basic research).Three experiments were carried out with various pre-sowing treatments.These treatments included full or partial removal of seed coat(perisperm),partial cutting of cotyledons as well as moist chilling at 5℃ for 13 days and/or soaking the seeds in water or 250 ppm gibberellic acid(GA_(3))solution for 24 h.According to the results,cotyledons excision resulted in delayed germination,regardless of the presence or absence of the seed coat in comparison with the decoated seeds that demonstrated the highest germination rate amongst them.In addition,even the partial excision of seed coats affected positively both the germinability and the germination rate,compared to the control-intact seeds.Furthermore,control-intact seeds had a higher germination percentage when exposed to moist chilling independently of the application or not of gibberellin;while the combination of gibberellin application and moist chilling improved both the percentage and the rate of germination of decoated seeds.In conclusion,the role of perisperm(seed coat)in the germination procedure of loquat seeds seems to be important,indicating the existence of seed coat-imposed dormancy on loquat seeds.Finally,the existence of a mild endogenous embryo-dormancy on loquat is also discussed.

Whole genome re-sequencing of sweet cherry(Prunus avium L.)yields insights into genomic diversity of a fruit species

Sweet cherries,Prunus avium L.(Rosaceae),are gaining importance due to their perenniallity and nutritional attributes beneficial for human health.Interestingly,sweet cherry cultivars exhibit a wide range of phenotypic diversity in important agronomic traits,such as flowering time and defense reactions against pathogens.In this study,wholegenome resequencing(WGRS)was employed to characterize genetic variation,population structure and allelic variants in a panel of 20 sweet cherry and one wild cherry genotypes,embodying the majority of cultivated Greek germplasm and a representative of a local wild cherry elite phenotype.The 21 genotypes were sequenced in an average depth of coverage of 33.91×.and effective mapping depth,to the genomic reference sequence of‘Satonishiki’cultivar,between 22.21×to 36.62×.Discriminant analysis of principal components(DAPC)with SNPs revealed two clusters of genotypes.There was a rapid linkage disequilibrium decay,as the majority of SNP pairs with r2 in near complete disequilibrium(>0.8)were found at physical distances less than 10 kb.Functional analysis of the variants showed that the genomic ratio of non-synonymous/synonymous(dN/dS)changes was 1.78.The higher dN frequency in the Greek cohort of sweet cherry could be the result of artificial selection pressure imposed by breeding,in combination with the vegetative propagation of domesticated cultivars through grafting.The majority of SNPs with high impact(e.g.,stop codon gaining,frameshift),were identified in genes involved in flowering time,dormancy and defense reactions against pathogens,providing promising resources for future breeding programs.Our study has established the foundation for further large scale characterization of sweet cherry germplasm,enabling breeders to incorporate diverse germplasm and allelic variants to fine tune flowering and maturity time and disease resistance in sweet cherry cultivars.

Prunus genetics and applications after de novo genome sequencing:achievements and prospects

Prior to the availability of whole-genome sequences,our understanding of the structural and functional aspects of Prunus tree genomes was limited mostly to molecular genetic mapping of important traits and development of EST resources.With public release of the peach genome and others that followed,significant advances in our knowledge of Prunus genomes and the genetic underpinnings of important traits ensued.In this review,we highlight key achievements in Prunus genetics and breeding driven by the availability of these whole-genome sequences.Within the structural and evolutionary contexts,we summarize:(1)the current status of Prunus whole-genome sequences;(2)preliminary and ongoing work on the sequence structure and diversity of the genomes;(3)the analyses of Prunus genome evolution driven by natural and man-made selection;and(4)provide insight into haploblocking genomes as a means to define genome-scale patterns of evolution that can be leveraged for trait selection in pedigree-based Prunus tree breeding programs worldwide.Functionally,we summarize recent and ongoing work that leverages whole-genome sequences to identify and characterize genes controlling 22 agronomically important Prunus traits.These include phenology,fruit quality,allergens,disease resistance,tree architecture,and self-incompatibility.Translationally,we explore the application of sequence-based marker-assisted breeding technologies and other sequence-guided biotechnological approaches for Prunus crop improvement.Finally,we present the current status of publically available Prunus genomics and genetics data housed mainly in the Genome Database for Rosaceae(GDR)and its updated functionalities for future bioinformatics-based Prunus genetics and genomics inquiry.

Decoding altitude-activated regulatory mechanisms occurring during apple peel ripening

Apple(Malus domestica Borkh)is an important fruit crop cultivated in a broad range of environmental conditions.Apple fruit ripening is a physiological process,whose molecular regulatory network response to different environments is still not sufficiently investigated and this is particularly true of the peel tissue.In this study,the influence of environmental conditions associated with low(20 m)and high(750 m)altitude on peel tissue ripening was assessed by physiological measurements combined with metabolomic and proteomic analyses during apple fruit development and ripening.Although apple fruit ripening was itself not affected by the different environmental conditions,several key color parameters,such as redness and color index,were notably induced by high altitude.Consistent with this observation,increased levels of anthocyanin and other phenolic compounds,including cyanidin-3-O-galactoside,quercetin-3-O-rhamnoside,quercetin-3-O-rutinoside,and chlorogenic acid were identified in the peel of apple grown at high altitude.Moreover,the high-altitude environment was characterized by elevated abundance of various carbohydrates(e.g.,arabinose,xylose,and sucrose)but decreased levels of glutamic acid and several related proteins,such as glycine hydroxymethyltransferase and glutamate–glyoxylate aminotransferase.Other processes affected by high altitude were the TCA cycle,the synthesis of oxidative/defense enzymes,and the accumulation of photosynthetic proteins.From the obtained data we were able to construct a metabolite-protein network depicting the impact of altitude on peel ripening.The combined analyses presented here provide new insights into physiological processes linking apple peel ripening with the prevailing environmental conditions.

Apple whole genome sequences:recent advances and new prospects

In 2010,a major scientific milestone was achieved for tree fruit crops:publication of the first draft whole genome sequence(WGS)for apple(Malus domestica).This WGS,v1.0,was valuable as the initial reference for sequence information,fine mapping,gene discovery,variant discovery,and tool development.A new,high quality apple WGS,GDDH13 v1.1,was released in 2017 and now serves as the reference genome for apple.Over the past decade,these apple WGSs have had an enormous impact on our understanding of apple biological functioning,trait physiology and inheritance,leading to practical applications for improving this highly valued crop.Causal gene identities for phenotypes of fundamental and practical interest can today be discovered much more rapidly.Genome-wide polymorphisms at high genetic resolution are screened efficiently over hundreds to thousands of individuals with new insights into genetic relationships and pedigrees.High-density genetic maps are constructed efficiently and quantitative trait loci for valuable traits are readily associated with positional candidate genes and/or converted into diagnostic tests for breeders.We understand the species,geographical,and genomic origins of domesticated apple more precisely,as well as its relationship to wild relatives.The WGS has turbo-charged application of these classical research steps to crop improvement and drives innovative methods to achieve more durable,environmentally sound,productive,and consumer-desirable apple production.This review includes examples of basic and practical breakthroughs and challenges in using the apple WGSs.Recommendations for“what’s next”focus on necessary upgrades to the genome sequence data pool,as well as for use of the data,to reach new frontiers in genomics-based scientific understanding of apple.

Genetic Variation in Resistance to Valsa canker is Related to Arbutin and Gallic Acid Content in Pyrus bretschneideri

Pear Valsa canker is a fungal trunk disease caused by Valsa pyri. Phenolic compounds are ubiquitous in plants and usually contribute to plant resistance against biotic stress. To investigate the association between phenolic compounds and level of resistance to V. pyri, we quantified the contents of individual phenolic compounds in the cortex and phloem of stems from 8 cultivars of Pyrus bretschneideri. Significant variation in the levels of all compounds was found among the cultivars. Correlation analysis revealed an inverse correlation between levels of arbutin and gallic acid with the degree of canker resistance. This suggested that these phenolic compounds are beneficial to V. pyri infection. These data could be valuable for breeding cultivars of P. bretschneideri with greater resistance to V. pyri.