Effects of 1-methylcyclopropene on skin greasiness and quality of'Yuluxiang'pear during storage at 20℃

During storage at 20℃,specific pear cultivars may exhibit a greasy texture and decline in quality due to fruit senescence.Among these varieties,‘Yuluxiang’is particularly susceptible to peel greasiness,resulting in significant economic losses.Therefore,there is an urgent need for a preservative that can effectively inhibit the development of greasiness.Previous studies have demonstrated the efficacy of 1-methylcyclopropene(1-MCP)in extending the storage period of fruits.We hypothesize that it may also influence the occurrence of postharvest peel greasiness in the‘Yuluxiang’pears.In this study,we treated‘Yuluxiang’pears with 1-MCP.We stored them at 20℃while analyzing the composition and morphology of the surface waxes,recording enzyme activities related to wax synthesis,and measuring indicators associated with fruit storage quality and physiological characteristics.The results demonstrate that prolonged storage at 20℃leads to a rapid increase in skin greasiness,consistent with the observed elevations in L^(*),greasiness score,and the content of total wax and greasy wax components.Moreover,there were indications that cuticular waxes underwent melting,resulting in the formation of an amorphous structure.In comparison to controls,the application of 1-MCP significantly inhibited increments in L^(*) values as well as grease scores while also reducing accumulation rates for oily waxes throughout most stages over its shelf period,additionally delaying transitions from flaky-wax structures towards their amorphous counterparts.During the initial 7 d of storage,several enzymes involved in the biosynthesis and metabolism of greasy wax components,including lipoxygenase(LOX),phospholipase D(PLD),andβ-ketoacyl-CoA synthase(KCS),exhibited an increase followed by a subsequent decline.The activity of LOX during early shelf life(0–7 d)and the KCS activity during middle to late shelf life(14–21 d)were significantly suppressed by 1-MCP.Additionally,1-MCP effectively maintained firmness,total soluble solid(TSS)and titratable acid(TA)contents,peroxidase(POD),and phenylalanine ammonia-lyase(PAL)activities while inhibiting vitamin C degradation and weight loss.Furthermore,it restrained polyphenol oxidase(PPO)activity,ethylene production,and respiration rate increase.These findings demonstrate that 1-MCP not only delays the onset of peel greasiness but also preserves the overall storage quality of‘Yuluxiang’pear at a temperature of 20℃.This study presents a novel approach for developing new preservatives to inhibit pear fruit peel greasiness and provides a theoretical foundation for further research on pear fruit preservation.

Identification of S-RNase genotype and analysis of its origin and evolutionary patterns in Malus plants

Identification of the S genotype of Malus plants will greatly promote the discovery of new genes,the cultivation and production of apple,the breeding of new varieties,and the origin and evolution of self-incompatibility in Malus plants.In this experiment,88 Malus germplasm resources,such as Aihuahong,Xishuhaitang,and Reguanzi,were used as materials.Seven gene-specific primer combinations were used in the genotype identification.PCR amplification using leaf DNA produced a single S-RNase gene fragment in all materials.The results revealed that 70 of the identified materials obtained a complete S-RNase genotype,while only one S-RNase gene was found in 18 of them.Through homology comparison and analysis,13 S-RNase genotypes were obtained:S_(1)S_(2)(Aihuahong,etc.),S_(1)S_(28)(Xixian Haitang,etc.),S_(1)S_(51)(Hebei Pingdinghaitang),S_(1)S_(3)(Xiangyangcun Daguo,etc.),S_(2)S_(3)(Zhaiyehaitang,etc.),S_(3)S_(51)(Xishan 1),S_(3)S_(28)(Huangselihaerde,etc.),S_(2)S_(28)(Honghaitang,etc.),S_(4)S_(28)(Bo 11),S_(7)S_(28)(Jiuquan Shaguo),S_(10)S_e(Dongchengguan 13),S_(10)S_(21)(Dongxiangjiao)and S_(3)S_(51)(Xiongyue Haitang).Simultaneously,the frequency of the S gene in the tested materials was analyzed.The findings revealed that different S genes had varying frequencies in Malus resources,as well as varying frequencies between intraspecific and interspecific.S_(3) had the highest frequency of 68.18%,followed by S_(1)(42.04%).In addition,the phylogenetic tree and origin evolution analysis revealed that the S gene differentiation was completed prior to the formation of various apple species,that cultivated species also evolved new S genes,and that the S_(50) gene is the oldest S allele in Malus plants.The S_(1),S_(29),and S_(33) genes in apple-cultivated species,on the other hand,may have originated in M.sieversii,M.hupehensis,and M.kansuensis,respectively.In addition to M.sieversii,M.kansuensis and M.sikkimensis may have also played a role in the origin and evolution of some Chinese apples.

Comparison of transcriptome and metabolome analysis revealed differences in cold resistant metabolic pathways in different apple cultivars under low temperature stress

Freezing injury in winter is an important abiotic stress that seriously affects plant growth and development.Deciduous fruit trees resist freezing injury by inducing dormancy.However,different cultivars of the same species have different cold resistance strategies.Little is known about the molecular mechanism of apple trees in response to freezing injury during winter dormancy.Therefore,in this study,1-year-old branches of the cold-resistant cultivar‘Hanfu’(HF)and the cold-sensitive cultivar‘Changfuji No.2’(CF)were used to explore their cold resistance through physiological,biochemical,transcriptomics,and metabolomics analyses.Combining physiological and biochemical data,we found that HF had a stronger osmotic regulation ability and antioxidant enzyme activity than CF,as well as stronger cold resistance.The functional enrichment analysis showed that both cultivars were significantly enriched in pathways related to signal transduction,hormone regulation,and sugar metabolism under freezing stress.In addition,the differentially expressed genes(DEGs)encoding galactinol synthase,raffinose synthase,and stachyose synthetase in raffinose family oligosaccharides(RFOs)metabolic pathways were upregulated in HF,and raffinose and stachyose were accumulated,while their contents in CF were lower.HF accumulated 4-aminobutyric acid,spermidine,and ascorbic acid to scavenge reactive oxygen species(ROS).While the contents of oxidized glutathione,vitamin C,glutathione,and spermidine in CF decreased under freezing stress,consequently,the ability to scavenge ROS was low.Furthermore,the transcription factors apetala 2/ethylene responsive factor(AP2/ERF)and WRKY were strongly induced under freezing stress.In summary,the difference in key metabolic components of HF and CF under freezing stress is the major factor affecting their difference in cold resistance.The obtained results deepen our understanding of the cold resistance mechanism in apple trees in response to freezing injury during dormancy.

MdAIL5 overexpression promotes apple adventitious shoot regeneration by regulating hormone signaling and activating the expression of shoot development-related genes

Adventitious shoot(AS)regeneration is a significant factor in the genetic transformation of horticultural plants.It is also a noteworthy approach to their vegetative propagation.AS regeneration remains highly dependent on the genotype or maturity of explants.We here found that the AS regeneration abilities of apple leaves were positively correlated with MdAIL5 expression.MdAIL5 overexpression dramatically increased AS regeneration efficiency.Notably,MdAIL5 overexpression could restore the AS formation ability of explants to a certain extent,which was lost with an increase in maturity.Endogenous hormone detection revealed that MdAIL5 overexpression changed the contents of auxin,cytokinin(CK),and other hormones in apple leaves.Transcriptome analysis revealed that many genes related to auxin,CK,and brassinolide signaling pathways were significantly and differentially expressed between MdAIL5-overexpressing transgenic apple and wild-type apple plants.Yeast one-hybrid assays,the electrophoretic mobility shift assay,and the dual-luciferase reporter assay revealed that MdAIL5 directly binds to MdARF9 and MdHB14 promoters and positively affects their expression.We here established a model of MdAIL5 regulating AS formation,which acts as a theoretical basis for facilitating genotype-or explant maturity-independent AS regeneration in the future.

Isolation,identification and artificial inoculation of Rhizoctonia solani on pear during storage

Pear is a fruit crop of worldwide importance and cold storage is an integral part of the production and distribution of pears.An uncharacterized fungal disease has been observed on‘Huangguan’pear fruit during cold storage in Hebei Province.The fungus was consistently isolated from diseased fruit by routine tissue separation method,and shown to be the causal agent according to Koch postulates.Based on its morphology,molecular characteristics,pathogenicity and ITS sequence,the fungus was identified as Rhizoctonia solani.This study recorded postharvest fruit rot caused by Rhizoctonia solani on pear fruit in China.

Comparative transcriptome analysis reveals key genes and pathways in response to Alternaria alternata apple pathotype infection

Apple leaf spot,caused by the Alternaria alternata apple pathotype(AAAP),is an important fungal disease of apple.To understand the molecular basis of resistance and pathogenesis in apple leaf spot,the transcriptomes of two apple cultivars‘Hanfu'(HF)(resistant)and‘Golden Delicious'(GD)(susceptible)were analyzed at 0,6,18,24 and 48 h after AAAP inoculation by RNA-Seq.At each time point,a large number of significantly differentially expressed genes(DEGs)were screened between AAAP-inoculated and uninoculated apple leaves.Analysis of the common DEGs at four time points revealed significant differences in the resistance of‘HF'and‘GD'apple to AAAP infection.RLP,RNL,and JA signal-related genes were upregulated in both cultivars to restrict AAAP development.However,genes encoding CNLs,TNLs,WRKYs,and AP2s were only activated in‘HF'as part of the resistance response,of which,some play major roles in the regulation of ET and SA signal transduction.Further analysis showed that many DEGs with opposite expression trends in the two hosts may play important regulatory roles in response to AAAP infection.Transient expression of one such gene MdERF110 in‘GD'apple leaves improved AAAP resistance.Collectively,this study highlights the reasons for differential resistance to AAAP infection between‘HF'and‘GD'apples which can theoretically assist the molecular breeding of disease-resistant apple crops.

Effects of different color paper bags on aroma development of Kyoho grape berries

This study investigated the influence of red,green,blue,and white paper bags on the free volatile compound development of Kyoho grape berries from green to harvest.Seven functional groups of volatiles were identified during the development of Kyoho grape berries including esters,aldehydes,alcohols,terpenes,ketones,acids,and hydrocarbons.Esters and aldehydes were abundant in Kyoho grape berries,mainly represented by ethyl acetate,ethyl butyrate,and(E)-2-hexenal.They accumulated quickly after veraison and slightly decreased toward maturation.Red,green,blue,and white paper bags promoted the accumulation of esters and inhibited the accumulation of aldehydes,also inhibited the accumulation of alcohols,tepenes,ketones,and acids.Their effect from strong to weak was green,blue,red,and white paper bags.The expression profiles of genes in the lipoxygenase-hydroperoxide lyase(LOX-HPL) pathway were also analyzed and the results indicated that the regulation of red,green,blue,and white paper bags on aldehydes,alcohols,and esters volatile aromas was at transcriptional level.The results expanded our comprehension in grape aroma biosynthesis and berry bagging technique in table grape cultivation.

Optimal storage temperature and 1-MCP treatment combinations for different marketing times of Korla Xiang pears

Maintenance of green color is the primary indicator of quality in the market evaluation of Korla Xiang pears at present and can generally be achieved through early harvesting and decreasing the storage temperature, but the fruit quality was reduced by early harvesting, and the decreasing storage temperature increased the risk of chilling injury. The objectives of this study were to determine the optimal storage parameters for different storage times and to find ways to preserve the green skin color of pears. Specifically, we analyzed the effects of the ethylene inhibitor, 1-methylcyclopropene （1-MCP）, combined with low temperature on quality and maintenance of the green color of Korla Xiang pears during storage. We found that 1-MCP and/or low temperature reduced the loss of green color at 20℃ after being removed from cold storage. In addition, 1-MCP significantly inhibited the decline of titratable acid and ascorbic acid but had no significant effect on fruit firmness and total soluble solids. Low temperature with or without 1-MCP inhibited the release of ethylene, inhibited the decline in the stalk preservation index, inhibited the increase in decay rate and weight loss rate during storage, and inhibited the increase in the core browning index after 225 days of storage. Different storage temperatures had different effects on the quality of Korla Xiang pears. Despite inhibiting ethylene release, a storage temperature of-1.5℃ increased the respiration rate. Storage at -1.5℃ caused core browning eady during storage due to chilling injury, whereas at 2℃ core browning occurred late during storage due to senescence. In late storage, 1-MCP had no significant effect on the maintenance of Korla Xiang pear quality at 2℃. Based on these results, we determined the optimal combinations of low temperature and 1-MCP treatment to maintain pear quality while avoiding chilling injury. For different marketing times, the optimal conditions for storage until New Year＇s Day （a storage duration of 90 days） are 2℃ or 1-MCP combined with 2℃. For storage until the Spring Festival （a storage duration of 150 days）, the optimal conditions are 0℃ or 1-MCP combined with 0℃, and for storage until May （a storage duration of 225 days）, the best conditions are 1-MCP combined with -1.5℃.

Molecular characterization of Apple necrotic mosaic virus identified in crabapple(Malus spp.) tree of China

Apple necrotic mosaic virus(ApNMV) was identified in crabapple trees with mosaic symptoms from Zaozhuang, Shandong Province, China, by reverse transcription polymerase chain reaction(RT-PCR) analysis. The complete nucleotide sequences of one isolate from crabapple(ApNMV-Hai) and two isolates from apple(ApNMV-Hua and-Qu) were determined. The sizes of genomic RNA1, 2 and 3 of the three isolates differed from those of the previously reported isolate ApNMV-P126 from Japanese apple, especially RNA3. Compared with the nucleotide(nt) sequence of RNA3 in isolate P126, those in the Hai and Qu isolates were 7 and 33 nt shorter, respectively, and that of isolate Hua was 7 nt longer. Alignment analyses showed that these differences in size were mainly due to differences in the lengths of the 5′ untranslated region(UTR) and the UTR region between the ORFs encoding the movement protein and the coat protein. In the phylogenetic trees constructed using the full genomic sequences of RNA1, 2 and 3, the isolate Hai clustered into a group with the isolate Qu in the RNA1 tree, but formed an individual branch in the RNA2 and 3 trees. Three recombination events were identified in the nucleotide sequences of RNA1 and 2 among the isolates ApNMV-Hai,-Hua, and-Qu. This is the first report of the full genome sequence of ApNMV in crabapple.

An assessment of the genetic diversity of pear(Pyrus L.)germplasm resources based on the fruit phenotypic traits

Germplasm resources are an important basis for genetic breeding and analysis of complex traits,and research on genetic diversity is conducive to the exploration and creation of new types of germplasm.In this study,the distribution frequency,coefficient of variation,Shannon-Wiener index,and variance and cluster analyses were used to analyze the diversity and trait differences of 39 fruit phenotypic traits from 570 pear accessions,which included 456 pear accessions from 11 species and 114 interspecific hybrid cultivars that had been stored in the National Germplasm Repository of Apple and Pear(Xingcheng,China).The comprehensive evaluation indices were screened by correlation,principal component and regression analyses.A total of 132 variant types were detected in 28 categorical traits of pear germplasm fruit,which indicate a rich diversity.The diversity indices in decreasing order were:fruit shape(1.949),attitude of calyx(1.908),flesh texture type(1.700),persistency of calyx(1.681),russet location(1.658),relief of area around eye basin(1.644),flavor(1.610)and ground color(1.592).The coefficient of variation of titratable acidity in the 11 numerical traits of pear germplasm fruit was as high as 128.43%,which could more effectively reflect the differences between pear accessions.The phenotypic differentiation coefficient V_(st)(66.4%)among the five cultivated pear species,including Pyrus bretschneideri(White Pear),P.pyrifolia(Sand Pear),P.ussuriensis(Ussurian Pear),P.sinkiangensis(Xinjiang Pear),and P.communis(European Pear),was higher than the within population phenotypic differentiation coefficient V_(st)(33.6%).The variation among populations was the main source of variation in pear fruit traits.A hierarchical cluster analysis divided the 389 accessions of six cultivated pear species,including P.pashia(Himalayan Pear),into six categories.There were certain characteristics within the populations,and the differences between populations were not completely clustered by region.For example,Sand Pear cultivars from Japan and the Korean Peninsula clustered together with those from China.Most of the White Pear cultivars clustered with the Sand Pear,and a few clustered with the Ussurian Pear cultivars.The Ussurian Pear and European Pear cultivars clustered separately.The Xinjiang Pear and Himalayan Pear did not cluster together,and neither did the cultivars.Seventeen traits,three describing fruit weight and edible rate(fruit diameter,fruit length and fruit core size),five describing outer quality and morphological characteristics(over color,amount of russeting,dot obviousness,fruit shape,and stalk length),and nine describing inner quality(flesh color,juiciness of flesh,aroma,flavor,flesh texture,flesh texture type,soluble solid contents,titratable acidity,and eating quality)were selected from the 39 traits by principal component and stepwise regression analyses.These 17 traits could reflect 99.3%of the total variation and can be used as a comprehensive evaluation index for pear germplasm resources.

High-throughput sequencing of highbush blueberry transcriptome and analysis of basic helix-loop-helix transcription factors

The highbush blueberry（Vaccinium corymbosum）,Duke,was used to construct a de novo transcriptome sequence library and to perform data statistical analysis.Mega 4,CLC Sequence Viewer 6 software,and quantitative PCR were employed for bioinformatics and expression analyses of the basic helix-loop-helix（BHLH）transcription factors of the sequencing library.The results showed that 28.38 gigabytes of valid data were obtained from transcriptome sequencing and were assembled into 108 033 unigenes.Functional annotation showed that 32 244 unigenes were annotated into Clusters of Orthologous Groups（COG）and Gene Ontology（GO）databases,whereas the rest of the 75 789 unigenes had no matching information.By using COG and GO classification tools,sequences with annotation information were divided into 25 and 52 categories,respectively,which involved transport and metabolism,transcriptional regulation,and signal transduction.Analysis of the transcriptome library identified a total of 59 BHLH genes.Sequence analysis revealed that 55 genes of that contained a complete BHLH domain.Furthermore,phylogenetic analysis showed that BHLH genes of blueberry（Duke）could be divided into 13 sub-groups.PCR results showed that 45 genes were expressed at various developmental stages of buds,stems,leaves,flowers,and fruits,suggesting that the function of BHLH was associated with the development of different tissues and organs of blueberry,Duke.The present study would provided a foundation for further investigations on the classification and functions of the blueberry BHLH family.

The Relation Between Endogenous Hormones and Late-Germination in Buds of Avrolles Apple

In order to provide the physiological bases for selecting late-germination cultivars that can avoid late frost damage, the very late-germination variety Avrolles （Malus domestica） was used to study the relation between the dynamic changes and balance of endogenous hormones and germination time. The concentrations of endogenous GA3, ABA, IAA, and ZR were determined in buds of Avrolles and Judeline （Malus domestica） from dormancy releasing to germination by capillary electrophoresis. The dynamic changes of endogenous hormones concentration in buds of Avrolles and Judeline were similar; but the magnitude and time of the change were significantly different between the two varieties, especially for GA3. GA3 concentration increased with dormancy releasing, then decreased, and increased again before germination in the two varieties. GA3 concentration in Avrolles was 1.72 times that in Judeline at the first peak, the gap increased to 2.22 times at germination. ZR concentration exhibited a continuous increase trend, but it decreased sharply before germination. ZR accumulation in Avrolles took 36 days longer than in Judeline, the peak value was 44% higher than in Judeline. Before germination, ZR concentration in Avrolles was 2.12 times that in Judeline. The differences between IAA and ABA concentration were relatively small in the two varieties, while the ratios of GA3/ABA and （GA3 ＋ IAA ＋ ZR）/ABA in Avrolles were 2.08 and 1.58 times those in Judeline, respectively. The germination of apple bud was regulated by the endogenous hormones. For the late-germination apple Avrolles, its germination requires higher concentration of GA3 and ZR, which leads to the high ratios of GA3/ABA and （GA3＋ IAA＋ ZR）/ABA.

First report of Athelia bombacina causing postharvest fruit rot on pear

Pear is an important fruit crop in the world. An uncharacterized disease has been observed on pear fruits during cold storage ir~ Suning, Shenzhou, Xinji and other locations in Hebei Province, China. The incidence rate of the disease has reached 10%, and sometimes up to 20%. A particular fungus was consistently isolated from the infected pear fruit and cultured. Based on its morphology, molecular characteristics, pathogenicity and ITS sequence, the fungus was identified as Athelia bombacina. To our knowledge, this is the first report of Athelia bombacina causing postharvest fruit rot on pear.

Differences of aroma development and metabolic pathway gene expression between Kyoho and 87-1 grapes

Aroma is an important quality trait of grapes and often the focus of consumers,viticulturists and grapevine breeders.Kyoho is a hybrid between Vitis vinifera and Vitis labrusca with a strawberry-like scent,while 87-1 is an early-ripening mutant of Muscat hamburg,belonging to Vitis vinifera,with a rose scent.In this study,we compared their aroma compositions and concentrations during berry development by headspace-SPME combined with gas chromatography-mass spectrometry(GC-MS),and analyzed the expression differences of enzyme-encoding genes in the LOX-HPL,MEP and MVA metabolic pathways by qRT-PCR.Twelve esters were detected in Kyoho during the whole berry development and they were abundant after veraison,but no esters were detected in 87-1 berries.Linalool was the dominant terpene among the 14 terpenes detected in 87-1 berries,while limited amounts of terpenes were detected in Kyoho berries.qRT-PCR analysis indicated that the low expression of VvAAT might explain the low content of ester volatiles in 87-1 berries,and the low expression of coding genes in the MEP pathway,especially VvPNLin Ner1,might be the reason for the low content of volatile terpenes in Kyoho berries.The results from this work will promote our understanding of aroma metabolic mechanisms of grapes,and offer some suggestions for grape aromatic quality improvement.

Analysis of genetic diversity and structure across a wide range of germplasm reveals genetic relationships among seventeen species of Malus Mill,native to China

China is a center of diversity for Malus Mill,with 27 native species including 21 wild species and six domesticated species.We applied a set of 19 simple sequence repeat markers to genotype 798 accessions of 17 species(12 wild species and five cultivated species)of Malus originating from 14 provinces in China.A total of 500 alleles were detected.Diversity statistics indicated a high level of genetic variation as quantified by the average values of the effective allele number(N_(e)).expected heterozygosity(H_(e)),and Shannon's Information Index(I)(10.309,0.886,and 2.545,respectively).Malus sieversii(MSR;H_(e)=0.814,I=2.041,N_(e)=6.054),M.baccata(MBB;H_(e)=0.848,/=2.350,N_(e)=8.652),M.toringoides(MTH;He=0.663,I=1.355,N_(e)=3.332),and M.hupehensis(MHR;H_(e)=0.539,I=0.912,N_(e)=0.579)showed a higher level of genetic diversity in this study than the previous studies.MSR and MBB contributed to the origin and evolution of some accessions of M.domestica subsp.chinensis(MDC).However,other accessions of MDC showed a closer genetic distance with MBB and cultivated species,especially M.robusta(MRB),M.asiatica(MAN),and M.prunifolia(MPB).Not all accessions of MDC were descended from MSR in Xinjiang Uygur Autonomous Region of China.This research provides novel insights into the genetic relationships of Malus native to China,which will be useful for genetic association studies,germplasm conservation,and breeding programs.

Effect of pre-culture on virus elimination from in vitro apple by thermotherapy coupled with shoot tip culture

We evaluated the role of pre-culture on survival rate of in vitro apple plants treated by thermotherapy. Two apple cultivars, Malusxdomestica cv. Pink Lady and Huafu, were used in the experiment and both have widely grown in China and infected with Apple chlorotic leafspot virus （ACLSV） and Apple stem grooving virus （ASGV）. Results in growth and virus titer of apple plants did not exhibit clear trends during five different periods of pre-culture. Whilst, pre-culture increased the survival rate of the two cultivars during thermotherapy. The survival rate of plants pre-cultured for 13 d （P-13d） was 14 and 51% higher than that of P-ld plants for Pink Lady and Huafu, respectively. Moreover, pre-culture positively influenced regeneration of Huafu plants. The average survival rate of plants regenerated from P-ld and P-4d was 20% lower than that regenerated from P-7d, P-10d, and P-13d. The efficiency of virus eradication was determined by reverse-transcription PCR with two primer pairs for each virus, and the detection results showed that pre-culture scarcely affected apple virus elimination. Despite the fact that the two viruses were hardly detected at 5 d of thermotherapy, no virus-free plants were found in the two cultivars of regenerated apple plantlets after 30-d treatment.

A 14 nucleotide deletion mutation in the coding region of the PpBBX24 gene is associated with the red skin of“Zaosu Red”pear(Pyrus pyrifolia White Pear Group):a deletion in the PpBBX24 gene is associated with the red skin of pear

Red skin is an important quality trait for pear fruits and is determined by the concentration and composition of anthocyanins.The regulatory mechanism underlying anthocyanin accumulation is a popular topic in fruit research.Red mutants are ideal materials for studying the molecular mechanism of color diversity in pear.Although several red pear mutants have been cultivated and are in production,no exact locus containing the responsible genetic mutation has been identified.In this study,by combining the bulked segregant analysis with whole-genome sequencing,we identified a 14 nucleotide deletion mutation in the coding region of the PpBBX24 gene from the red pear mutant“Zaosu Red”.We further verified that the deletion was present only in the red mutant of“Zaosu”and in its red offspring,which was different from that which occurred in other red pear fruits.This deletion results in a coding frame shift such that there is an early termination of the PpBBX24 gene and loss of key NLS and VP domains from PpBBX24.The lost domains may reduce or alter the normal function of PpBBX24.In addition,we found that the transcript levels of the PpMYB10 and PpHY5 genes in red samples were significantly higher than those in green samples,whereas the results for the normal-type PpBBX24 gene were the opposite.We ultimately revealed that the 14 nucleotide deletion mutation in the coding region of the PpBBX24 gene is associated with the red skin of the“Zaosu Red”pear.This finding of somatic mutational events will be helpful for breeding new red pear cultivars and for understanding the regulatory mechanisms involved in pear skin pigmentation.

Genotype-specific suppression of multiple defense pathways in apple root during infection by Pythium ultimum

The genotype-specific defense activation in the roots of perennial tree crops to soilborne necrotrophic pathogens remains largely unknown.A recent phenotyping study indicated that the apple rootstock genotypes B.9 and G.935 have contrasting resistance responses to infection by Pythium ultimum.In the current study,a comparative transcriptome analysis by Illumina Solexa HiSeq 3000 platform was carried out to identify the global transcriptional regulation networks between the susceptible B.9 and the resistant G.935 to P.ultimum infection.Thirty-six libraries were sequenced to cover three timepoints after pathogen inoculation,with three biological replicates for each sample.The transcriptomes in the roots of the susceptible genotype B.9 were reflected by overrepresented differentially expressed genes(DEGs)with downregulated patterns and systematic suppression of cellular processes at 48 h post inoculation(hpi).In contrast,DEGs with annotated functions,such as kinase receptors,MAPK signaling,JA biosynthesis enzymes,transcription factors,and transporters,were readily induced at 24 hpi and continued upregulation at 48 hpi in G.935 roots.The earlier and stronger defense activation is likely associated with an effective inhibition of necrosis progression in G.935 roots.Lack of effector-triggered immunity or existence of a susceptibility gene could contribute to the severely disturbed transcriptome and susceptibility in B.9 roots.The identified DEGs constitute a valuable resource for hypothesis-driven studies to elucidate the resistance/tolerance mechanisms in apple roots and validating their potential association with resistance traits.

Prevalence and genetic diversity of grapevine fabavirus isolates from different grapevine cultivars and regions in China

A total of 288 grapevine samples of 61 different grapevine cultivars,collected from 22 provinces and regions,were analyzed by reverse transcription-PCR(RT-PCR) for the presence of grapevine fabavirus(GFabV).PCR detection results showed the incidences of GFabV were 12.8%(30/235) and 48.1%(25/52) in the asymptomatic and symptomatic vines,respectively.The genetic diversity of GFabV isolates was analyzed based on partial nucleotide and encoded amino acid sequences of the RNA1 and RNA2 polyprotein genes.Phylogenetic analyses of the RNA1 and RNA2 gene sequences divided the GFabV isolates into five well-defined groups.Groups 1,2,and 4 comprised only Chinese isolates.This article represents the first report for the prevalence and genetic diversity of GFabV in grapevines grown in China.

Species-specific PCR-based assays for identification and detection of Botryosphaeriaceae species causing stem blight on blueberry in China

Botryosphaeriaceae species are important causal agents of blueberry stem blight worldwide. Blueberry stem blight has become an important disease, potentially affecting the quality and production of blueberries in China. It is difficult and time-consuming to identify at the species level using morphological methods. The aim of this study was to develop polymerase chain reaction（PCR） assays for the diagnosis and early detection of latent infections of blueberry stems by Botryosphaeria spp. Species-specific primers, based on the ribosomal DNA internal transcribed spacer region and β-tubulin gene, were designed and selected for use in PCR assays. Three primer pairs, Lt347-F/R for Lasiodiplodia theobromae, Np304-F/R for Neofusicoccum parvum and FaF/Bt2b for Botryosphaeria dothidea, successfully amplified specific PCR fragments of different sizes on pure cultures or from blueberry stems inoculated and naturally infected blueberry plants with three pathogens, respectively. These primers did not amplify any PCR fragments from other blueberry stem disease-associated pathogens, such as Phomopsis spp. and Pestalotiopsis spp. This PCR protocol could detect as low as 1 00 pg to 1 ng of purified fungal DNA. This PCR-based protocol could be used for the diagnosis and detection of these pathogens from pure cultures or from infected blueberry plants.