Citrus genetic improvement has achieved a great progress during the last six decades in China. A repository harboring more than 1 700 accessions of Rutaceae in Chongqing and an embryogenic callus collection including more than 100 varieties in Wuhan have been established,respectively. Continuing exploration of citrus germplasm resulted in the identification of wild Daoxian tangerine,Honghe papeda and the mini-citrus,a mono-embryonic Hongkong kumquat for functional genmics research. A new type of rootstock,Ziyang Xiangcheng（Citrus junos）has been utilized in Chinese citrus industry. A total of 122 citrus varieties including 121 for scion and one for rootstock have been registered or protected by PVP. Out of the scion varieties,88.5% is from the natural mutation including the bud-sport and chance seedling variation,and the rest from artifically created mutants,such as the irradiation,hybridization and protoplast fusion etc. These varieties covered nearly all types of citrus,including loose-skin mandarin,sweet orange and pummelo etc,with improved seedlessness,mature season and fruit color etc. The omics technologies have been widely used in citrus genetic improvement in China. Genomes including sweet orange and other main citrus species have been sequenced and assembled during the recent decade,as has accelerated cloning of the key genes controlling import agronomic traits,such as the polyembryonic related gene CitRWP etc. Genetic transformation and gene editing are also setup in Citrus. These achievments have laid a solid base for citrus genome-design breeding for the future.

‘Huangjinmi’，a new early-ripening table grape cultivar with muscat flavor，is derived from the cross of‘Red Globe’and‘Xiangfei’. The average cluster weight is 703.5 g，and the average single berry weight is 9.5 g. The berry is round，yellow-green or golden yellow，crisp and hard. The soluble solids content is 19.0%，and the titratable acid content is 0.58%. It had a high yield（26 300 kg · hm^-2），early bearing，and long shelf life. It is suitable for open field and protected cultivation in the Beijing，Tianjin，Hebei and other areas with similar ecological conditions，and for rain shelter cultivation in the rainy regions of the South.

To explore the role of peroxidase（POD）gene family members under stress conditions in apples,51 apple POD（MdPOD）family members were identified through multiple sequence alignments in which the reported Arabidopsis thalianaPOD genes were adopted,and their expression under stresses are analyzed. The results show that the 51 family members scatter in 13 chromosomes,encoding 95 to 1 433 amino acids,protein molecular weight ranges 10.18 to 161.02 kD,and isoelectric point（pI）ranges from 4.36 to 9.90. Further analysis indicates that the gene family is divided into six subfamilies,and the number of exon is 1 to 40. Selective pressure analysis shows that 20 gene pairs are subjected to purification selection in the evolutionary process. Subcellular localization shows that MDPOD15 is mainly presented in the cell membrane,cytoplasm,nucleus and chloroplast. The expression profile of gene chips displays that MdPOD are highly expressed in apple’s flowers,leaves and fruits. Real-time quantitative PCR （qRT-PCR）indicates that the expressions of most genes increased after ABA treatment for 2 h,and then decreases. Under PEG treatment,the expressions of 51 MdPODgenes firstly increase and reach the peak value at 12 h,while under the NaCl treatment,the expressions of MdPOD genes increase with the prolongation of time and reach the peak value at 24 h. The transient expression of MdPOD15 in tobacco leaves shows that MdPOD15 is expressed in the cell wall,cytoplasm and nucleus,and the overexpression of MdPOD15 in apple callus can mitigate the degree of cell damage caused by abiotic stress. Therefore,MdPOD genes may play different roles in different periods of time under different abiotic stresses.

The Pepper originated in the semi-arid area in central and southern Bolivia where the annual rainfall is less than 500 mm. This is a subtropical frost-free area. The original wild species are perennial herbs. According to the analysis and study of the starch granules,the Capsicum starch microfossils have been found dating from 8 000-7 500 years ago. Over thousands of years,Capsicum seeds spread out from Bolivia with the help of birds and indigenous peoples,thus spreading throughout South and Central America,then to the southwest of North America. In different ecological regions,more than 10 wild relatives and about 20 wild non-relatives of cultivated species have evolved. Capsicum cultivars evolved from the common ancestor Capsicum chacoense. The purple flower ancestors migrated to the Andes highlands and evolved to Capsicum pubescens. And the white flower ancestors migrated to the relatively dry area of southern Bolivia to evolve to Capsicum baccatum,continuing to migrate to the humid Amazon basin and evolve to the common ancestors of Capsicum annuum,Capsicum frutescens L. and Capsicum chinense Jacquin. They continued to migrate outward,evolving Capsicum annuum in Mexico and northern Central America,Capsicum frutescens L. in the Caribbean,and Capsicum chinense Jacquin in the northern valleys of the Amazon Basin. The pepper domestication started by removing the wild species from the original area for artificial cultivation. The wild species with the fruit small,single-color,upward-facing and easily falling off were domesticated into cultivated species with the fruit succulent,various-shaped,colorful,downward-facing,and not easy falling off,i.e. good economic benefits. Capsicum annuum was the first cultivated species domesticated in Mexico and Central America more than 6 000 years ago,and the other four cultivated species had been cultivated for at least 4 000 years,which are the oldest cultivated plants in America.

In order to explore the effect of brassinosteroids on the growth of apple plants under saline-alkali stress,apple rootstock Malus hupehensis with apomixis characteristics were used as experimental materials. The study investigated the effects of exogenous EBL（brassinosteroids analogs）on ion homeostasis,osmotic regulation,antioxidant system and pH balance of M. hupehensis under saline-alkali stress. The results showed that application of 0.2 mg · L^-1 exogenous EBL could significantly enhance the tolerance of M. hupehensis to saline-alkali stress. The main mechanisms were as follows:exogenous EBL could regulate the expression of Na⁺/K⁺ transporter genes and enhance the ratio of potassium to sodium to maintain ion homeostasis. Moreover,exogenous EBL could accumulate proline and soluble sugar to modulate osmotic stress,and enhance the activities of POD and CAT to alleviate oxidative damage under saline-alkali stress. Furthermore,exogenous EBL could decrease root pH by improving root secretion of organic acids and enhancing the expression of MhAHA2 and MhAHA8 genes. Exogenous EBL could also cooperate with auxin,gibberellin and dihydrozeatin responding to saline-alkali stress.

In order to study the role of apple ELO gene family in wax synthesis and cold resistance,bioinformatics methods were used to identify and analyze the ELO family members in the whole apple genome. The results showed that the MdELO gene family consisted of seven members,which were unevenly distributed on three apple chromosomes（Chr2,Chr8 and Chr15）. The MdELO protein contains 211-305 amino acid residues with isoelectric points ranging from 9.43 to 11.62. The results of subcellular localization showed that MdELO protein was distributed in the nucleus,cell membrane and chloroplast. The analysis of cis-acting elements showed that the 2 000 bp sequences upstream of the seven MdELO promoters were distributed with response elements such as hormones,environmental adaptability and stress induction. The wax content in different apple cultivars was further determined,and the results showed that the wax content of‘Oregon Spur Delicious’was significantly higher than that of‘Miyazaki’;On the other hand,from the it perspective of wax morphology and cuticle morphology,the wax of‘Oregon Spur Delicious’was needle-like and closely distributed,and the cuticle structure of its branches was close and smooth,while the wax of‘Miyazaki’was loose and lumpy,and the cuticle structure of its branches was loose and the surface was rough. Additionally,the proline,relative electrical conductivity and starch phosphorylase of the two apple branches increased firstly and then decreased with the extension of the overwintering period,and the amylase increased gradually,among which the content and activity of all indexes of‘Oregon Spur Delicious’were higher than that of‘Miyazaki’. The changes of the above indexes showed that the cold resistance of‘Oregon Spur Delicious’was significantly higher than that of‘Miyazaki’. It was found that the expression of ELO family members can be detected in the roots and leaves through qRT-PCR analysis,and the expression level displayeded certain differences. Most of them showed a trend of rising first and then falling,and the expression level is the highest at 12 h or 24 h,indicating that this family members may play an important role in low temperature stress.

In this article,the development history of protected horticulture in China during the last 60 years has been reviewed briefly including,the accomplishments of protected horticulture in China in industrial growth,scientific and technical innovation,talents training,and team platform construction. Moreover,the potential for future development and the main tasks of protected horticulture in China are prospected.

To explore the functions of SAUR（Small Auxin-up RNA）gene family in plant growth and development，bioinformatics methods were used to identify the SAUR genes in peach（Prunus persica）. The chromosome location，gene structure，evolutionary relationship and gene expression were analyzed，and the function of PpSAUR5 was verified through transgenic method. A total of 80 PpSAUR members were identified and divided into 12 subgroups，which were unevenly distributed on the eight chromosomes. The analysis of gene structure showed that 75 PpSAUR genes contained only one exon，and five genes contained two to three exons. Eighteen SAUR genes were found to be associated with tree growth through RNA-seq analysis. These genes exhibited different expression patterns in response to exogenous hormone.Among them，PpSAUR5 was induced by both IAA and GA. PpSAUR5 transgenic Arabidopsis exhibited longer petiole，hypocotyl，root，and less sensitivity to NAA and 2,4-D treatment than wild-type. The results indicated that PpSAUR5 functioned to promote organ elongation.

Anthocyanin is the main pigment affecting the skin color of apple fruit. In our previous study，MdSLC35F2-like was expressed at higher levels in the‘Nagafu 2’apple red bud mutant than in the wild-type. The open reading frame（ORF）of MdSLC35F2-like was cloned，it is 1 041bp，encoding 346 amino acids，which was predicted to be a hydrophobic α helix transmembrane protein with the highest homology to the PbSLC35F1-like of Pyrus × bretschneideri. Phylogenetic analysis showed that it had the closest evolutionary relationship with P. × bretschneideri，and the furthest evolutionary relationship with Theobroma cacao and Eucalyptus grandis. MdSLC35F2-like sequence and its expression rules before and after the fruit bagging were analyzed. After unbagging，the expression level of MdSLC35F2-like increased firstly，and then decreased with a peak on the third day. The expression level of MdSLC35F2-like in the two kinds of buds was significantly higher than that of‘Nagafu 2’. The above results indicated that the expression level of MdSLC35F2-like gene is positively correlated with anthocyanine content. Meanwhile，its expression levels in different color apple cultivars were compared. The expression of MdSLC35F2-like in red peel cultivars was significantly higher than that in green peel cultivars，and the expression level in red pulp cultivars was higher than that in non-red pulp cultivars. It suggests that MdSLC35F2-like may participate in the anthocyanine accumulation process.

Citrus canker,caused by is a bacterial disease,which severely influence citrus industry,and its pathogenicity is significantly enhanced under higher temperature and humidity environmental condition. HSP20 genes are abundant and highly conserved in higher plants,they play vital defense roles when plants are under biotic or abiotic stress. In order to investigate the role of HSP20 genes in response to Xanthomonas citri subsp. citri infection,the genes of HSP20 family in Citrus sinensis were identified. The analysis of biological information showed that there are 42 members,which can be divided into 11 subfamilies,they encode 135-373 aa and are distributed on nine chromosomes,their protein molecular weight are from 15.17 to 41.71 kD,isoelectric point are from 4.53 to 10.07,almost 92.9% of them not contain any intron or only one,and each subfamily share highly similar structures and conserved motifs,their promoter also has cis-acting elements response to hormones or stress. In order to access the role of CsHSP20 in response to Xcc and abiotic stress in resistant germplasm Citron C-05 with susceptible sweet orange,we have injected Xcc into the leaves of Citron C-05 and conducted a series of heat stress with small Citron C-05 plants. The relative expression levels of CsHSP20 have been screened by qRT-PCR,the results showed that HSP17.9,HSP23.3,HSP18.5 and HSP18.0 were up-regulated in both Xcc and heat stress,but their relative expression level in Citron C-05 is notably different from that of sweet orange under Xcc infection,especially HSP23.3. Interestingly,the induced expression patterns are consistent with the result of the transcriptomic analysis infected by Xcc. Then,these genes have been transiently overexpressed in sweet orange leaves,and Xcc quantitative analysis of Citron C-05 HSP23.3 showed that Xcc reproduction was inhibited.

Flavonoids are a class of secondary metabolites with ‘flavan’ skeleton and thousands of derivatives. The biosynthetic pathways of flavonoids are complicated，and some of them and related enzymes have been analyzed. Flavonoids play important roles in the growth and development of plants and the formation of flowers and fruits. Studies revealed that flavonoids can response to stresses and improve the tolerance and resistance of plants. This article reviews the biosynthetic pathways and molecular regulation mechanism of flavonoids in plants，the response of flavonoid pathways to different stresses，the main roles and mechanisms of flavonoids，and the future research directions. Thus，this article is expected to providing theoretical support for the targeted cultivation of horticultural crop varieties with highly resistant，deep processing，and product development.

Browning of pear flesh is an important problem affecting its quality. In this experiment，Browning varieties‘Baozhu’，‘Pingguoli’and non-browning varieties‘Fengshui’，‘Honghuada’were used to study the physiological mechanism of pear flesh browning，by measuring the changes of browning degree，phenolics and related enzyme activities during fruit development. The results showed that the browning degree，phenolic content and some enzyme activities of pear flesh decreased gradually with The growth and development of the fruit. Arbutin，chlorogenic acid and epicatechin were the main phenolic compounds in pear fruit from young fruit stage to mature fruit stage，accounting for more than 90% of the total phenolic content. The contents of arbutin and chlorogenic acid in the fruits of the two browning varieties were higher than those of the two non-browning varieties. According to the correlation analysis between fruit browning degree and phenolic substance content，single phenolic substance had little effect on fruit browning in young fruit stage，and phenolic substance strongly correlated with fruit browning in late fruit growth were arbutin，catechin，chlorogenic acid and caffeic acid. In the process of fruit growth and development，the PPO，PAL activities and total phenol content of browning varieties were higher than those of non-browning varieties. The PPO activity of the browning varieties was significantly different from that of the non-browning varieties at young fruit stage（P < 0.05），and it was not significantly different at mature fruit stage. The activities of PPO and PAL were significantly correlated with the contents of most phenolic substances in the fruits of the four varieties. The study on fruit browning at different development stages should take PPO activity and total phenolic content into consideration.

This review briefly summaries the processes for chrysanthemum development,and recalls the progress and main achievements that have been made in the germplasm resources,inheritance and molecular mechanisms underlying important traits formation,traditional breeding as well as modern biotechnology breeding programs during the last six decades in China. We also summarize the application status of modern biological technologies such as transgenic,genome editing,molecular marker-assisted selection,and multi-omics in the area of chrysanthemum genetics and breeding,and propose suggestions for the development of chrysanthemum genetics and breeding accordingly.

The effects of different numbers of leaves and fruit on plant growth,leaf photosynthetic characteristics,fruit quality and yield were studied in the cultivation of coconut husk in autumn and winter of tomato in greenhouse of North China,so as to obtain the optimal amount of functional leaves and fruit,which will provide a theoretical basis for improving the simplified technology of facility tomato production. A variety of large-fruit tomato named‘Fenkang 1’was used as the test material,seven ears of fruit were reserved for topping. Six treatments were set up,including 7,9 and 11 fully developed functional leaves from top to bottom with 3 fruit per ear（21 fruit in total）or 4 fruit per ear（28 fruit in total）. The photosynthesis and respiration of leaves in different canopy,development of leaves and fruit,quality and yield were analyzed. The results showed that,there were no significant differences in plant height and stem diameter after topping. The net photosynthetic rate（P_n）,light saturation point（LSP）,CO₂ saturation point（CSP）,apparent quantum efficiency（AQE）and carboxylation efficiency（CE）of the middle canopy leaves of 9-leaf with 21 fruit and 9-leaf with 28 fruit treatments were significantly higher than those of other treatments,while the dark respiration rate（R_d）is lower. The above parameters and chlorophyll content of the bottom canopy leaves were better for 7-leaf with 21 fruit and 7-leaf with 28 fruit treatments. The yields of single plant and single trough of 9-leaf with 28 fruit treatment were significantly higher than other treatments,besides,the fruit sugar-acid ratio was stable and optimal. To conclude,in the facility tomato production in North China,after reserved 7 ears fruit for topping,retaining 9 functional leaves and 4 fruit on each ear is the best way to regulate the amount of leaves and fruits. This technology can effectively improve population structure,facilitate the synthesis and accumulation of photosynthetic pigments,and effectively enhance the leaf photosynthesis,so as to improve the yield and maintain good quality of tomato.

‘Danxiahong’is a new red skin pear cultivar selected from the cross‘Zhongli 1’בHongxiangsu’. The shape of fruit is nearly round. The fruit size is big，and the average fruit weight is 260 g. The fruit skin is green covered with red on the side exposed to the sun. The flesh is white，crisp，rich juice，sweet，with litter fragrant. The soluble solids content is 13.5%. It matures in mid and late August in Zhengzhou City，Henan Province. The fruit have long storage life but not resistant to bumping. The yield is about 45 000 kg • hm-2 at full fruit stage.

‘Hongcuinuo’is a new high-quality and late-maturing litchi cultivar selected from open-pollinated seedlings of litchi in Guangdong. The average fruit weight is 23.6–28.6 g. The fruit is mostly long heart-shaped with scarlet skin，and the flesh tastes crisp and sweet（17.7%–19.1% TSS）. The seeds are generally aborted with an abortion ratio 90% and flesh recovery of 74.7%–81.1%. The contents of titratable acid，juice vitamin C and total sugar in the pulp were 0.15%–0.25%，0.77 mg • mL-1 and 160.5 g • L-1. The average yield of top grafting was 12 000 kg • hm-2 in the 5th year. The maturity period is early to mid July in Huilai County Guangdong Province.‘Hongcuinuo’is a promising cultivar for its high quality，late-maturity，good graft compatibility，easy to flower and fructify as well as high and stable yield.

This paper introduces the important achievements of pepper breeding over the past 60 years in China. It includes the collection,identification,evaluation,utilization and exploration of germplasm resources. The paper also discusses the important advancement in breeding technologies which includes heterosis utilization,anther culture,marker-assisted selection（MAS）,multiple resistance breeding and shuttle breeding. In addition,the history of pepper breeding is reviewed,including the traditional breeding before 1980s and the modern breeding guided with National scientific and technological research after 1980s. Then,driven by the industrial demands,China's pepper breeding has been undergoing several major optimizations：increasing yield,adjusting growth period,enhancing disease resistance,breeding for easy storage and transportation,breeding processed-food-specific varieties,improving product quality,and breeding for mechanized harvesting. After more than four decades of development,a modern and world-leading commercial pepper breeding system has been completely established. Domestic varieties with independent intellectual property rights are taking over 95% of market share across the country. Meanwhile,there are several unique advantages of in China's pepper breeding industry,such as low barrier to entry,low risk,high efficiency,large team,rich varieties,and high effectiveness. However,there are also several problems that strongly restrict the development of the pepper seed industry in China,including homogenization of pepper varieties,difficulty in expanding pepper seed business enterprises and slow research progress of pepper molecular breeding technology. Long-season varieties cultivated in green house and ornamental pepper varieties are mainly imported because the pepper breeding in China is still lagging behind developed countries. Therefore,the future directions for pepper breeding in China will be improving product quality,producing varieties suitable for mechanized production,breeding varieties with medicinal or other functional ingredients,exploring and advertising local varieties with excellent properties,and innovating novel breeding technologies.

In order to evaluate fruit morphological diversity of persimmon（Diospyros kaki Thunb.）,nine fruit quantitative traits,including longitudinal diameter,transverse diameter,lateral diameter,fruit shape index,stalk length,stalk diameter,pedicle length,pedicle width and fresh weight per fruit of 260 persimmon germplasm resources were determined. Subsequently,genetic diversity,correlation,cluster and principal component analysis were conducted on these traits. The results demonstrated high genetic diversities of the morphological traits. Variation coefficients of the nine morphological traits ranged from 16.98%（fruit shape index）to 50.57%（fresh weight per fruit）. Principal component analysis exhibited that the first three principal components with a cumulative contribution rate of 78.85% could represent all the nine morphological traits well. Based on the first and third principal components,the samples in this study were divided into five groups. Group Ⅰ and Ⅳ were suitable for breeding oblate spherical varieties;group Ⅱ and Ⅲ were suitable for breeding spherical varieties;group Ⅴ was suitable for breeding long spherical varieties;group Ⅳ was suitable for breeding large fruit varieties,and group Ⅱ was suitable for breeding small fruit size varieties.

The relationship among 5-aminolevulinic acid（ALA），abscisic acid（ABA）and auxin （IAA）in strawberry roots growth were discussed. It was found that exogenous ABA treatment significantly inhibited strawberry root growth，while ALA alleviated the inhibitory effect by ABA. ABA reduced the endogenous IAA content in the root tips of strawberry，while ALA promoted endogenous ABA content. The expressions of NCED1，NCED2 and CYP707A，referring to ABA biosynthesis and catabolism，respectively，were not different among treatments，whereas that of PYL4 and PYL8，both coding ABA receptors，and SnRK2.1，SnRK2.2，SnRK2.3，SnRK2.4，SnRK2.5 and SnRK2.6，which code the protein kinases in ABA signaling pathway were up-regulated by ABA but not mediated by ALA. These results suggested that the genes in ABA signaling route were not involved in ALA-ABA regulating root growth of strawberry. On the other hand，ABA down-regulated expressions of YUC2，YUC3（referring to IAA synthesis） and AUX1（coding auxin influx carrier）. However，the down-regulation of gene expressions by ABA were not reversed by ALA. This also means that these genes are not so important in ALA-ABA-regulated root growth of strawberry. Nevertheless，the expression of PIN1，which codes IAA exporter carrier，was down-regulated by ABA，and ALA reversed the down-regulation，suggesting that PIN1 may be involved in ALA-ABA regulating root growth of strawberry. In a transgenic Arabidopsis carrying the green fluorescent protein gene（GFP），it was found that AtPIN1-GFP expression was inhibited by ABA and reversed by ALA. Bioinformatic analysis showed that the amino acid sequence of FaPIN1 in the cultivated strawberry is high homology with many Rosaceous plants，with several transmembrane regions located at both ends of the polypeptide. When FaPIN1-GFP was transferred into tobacco （Nicotiana benthamiana），the fluorescence was distributed in the plasma membrane. When the cloned FaPIN1 was constructed into an estradiol-induced expression vector and transformed into Arabidopsis，the root growth of the transgenic plants was less sensitive to ABA treatment，and the ALA mitigation was also less significant. These results suggest that FaPIN1 is an important factor during ALA-ABA regulating root growth，and the alleviation of ALA on ABA-inhibiting root growth may be dependent on the promotion of IAA polar transport in the root tip of strawberry.

High-resolution single-cell RNA sequencing（scRNA-seq）technology based on high- throughput sequencing technology has been developed recently to resolve the heterogeneity of plant tissues at the single-cell level,identify distinct cell types in single tissue,and construct continuous cell differentiation trajectories and the transcriptional regulatory networks,in addition,it can search for rare cell types in tissues,thus deeply analyze molecular mechanisms of tissue development. To explore the application of scRNA-seq technology in plants,this paper reviews the progress of scRNA-seq technology and its application in plants. Firstly,the development course of scRNA-seq technology was overviewed; subsequently,we analyzed the progress of scRNA-seq technology in the identification of different plant tissue cell types,screening of specific expression marker genes for different cell types,and analyzing the continuous differentiation trajectories and transcriptional regulatory networks during the development of different plant tissues;finally,we summarized the challenges and future research directions of the

scRNA-seq technology applicating in plants,and aims to provide reference for the application of scRNA-seq technology in more plant species in the future.