Polyploid Gene Expression and Regulation in Polysomic Polyploids

Polyploidization is one of the most crucial pathways in introducing speciation and broadening biodiversity, especially in the Plant Kingdom. Although the majority of studies have focused only on allopolyploid or disomic polyploids, polysomic polyploid species have occurred frequently in higher plants. Due to the occurrence of the capabilities of more copies of alleles in a locus which can have additive dosage effects and/or allelic interactions, polysomic polyploids can lead to unique gene regulations to silence or adjust the expression level to create variations in organ size, metabolic products, and abiotic stress tolerance and biotic stress resistance, etc. This review aims to comprehensively summarize the contemporary understanding and findings concerning the molecular mechanisms of gene expression as well as gene regulation in natural typed and resynthesized polysomic polyploid plants. The review investigates the molecular level of phenomena in polysomic polyploid plants such as 1) typically enlarging organ size and stabilizing meiosis, 2) increasing phytochemical content and metabolic products, 3) enhancing the ability to adapt with biotic and abiotic stress, and 4) changing in gene regulation to silence or adjust the expression levels involve in sequence elimination, methylation, gene suppression, subfunctionalization, neo-functionalization, and transposon activation.

Study on Origin and Evolution of Polyploids in Parakmeria Hu et Cheng Using LEAFY Gene

[Objective] This study aimed to explore the origin and evolution of poly- poids in Parakmeria Hu et Cheng through LEAFY gene clone and sequence analysis. [Method] In this study, LEAFY gene in Parakmeria species and its relative genera was cloned and sequenced using molecular biology methods. With reference to LEAFY gene sequence published by NCBI, the origin pattern of polypoids in Parakmeria was explored and reasons for the distribution layout of different polypoids were analyzed through sequence alignment and phylogenetic analysis. [Result] Different Magnoliaceae species can be distinguished using the LEAFY gene, and there was a length polymorphism found in the 3＋ end of the LEAFY gene, which can be used to divide Magnoliaceae plants of different species or in different genera, thus of high application value. [Conclusion] Most Parakmeria tetraploids are produced by polyploidization of homologous chromosomes, while Parakmeria hexaploids are chiefly produced by both polyploidization of homologous chromosomes and heterologous hybridization.

Induction and characterization of polyploids from seeds of Rhododendron fortunei Lindl.

Most Rhododendron species are ornamental flowering species widely distributed in Asia,North America,and West Europe.Rhododendron fortunei,one of the endemic Rhododendron species in China,has beautiful flowers with bright colors and is being exploited to meet the needs of the flower market.Polyploid plants usually show superiority in growth,disease resistance,and adaption over their diploid relatives.Here,we report the first case of polyploid induction in R.fortunei.In order to induce polyploidy in R.fortunei,germinating seeds were treated with different concentrations of oryzalin for 16 h.By evaluating ploidy level with flow cytometry,a total of 34 polyploid R.fortunei lines,including 27 tetraploid lines and seven octoploid lines,were obtained.A comparison of treatments indicated that 7.5 mg L^-1 oryzalin was the optimal concentration for polyploid induction in seeds of R.fortunei.Compared with diploid plants,tetraploid and octoploid plants exhibited slower growth rates and had thicker and rounder curled leaves with more leaf epidermal hairs.Moreover,larger stomata at lower density were also observed in the leaves of polyploid plants.Chlorophyll contents were also significantly increased in polyploid plants,which leads to a darker green leaf color.Both small and large individuals exhibiting the same characteristics were observed among the obtained tetraploid plants.Overall,our study establishes a feasible method for polyploid induction in R.fortunei,thus providing a basis for breeding new R.fortunei varieties.

Natural and artificial polyploids in aquaculture

Genome polyploidy has been revealed to result in evolutionary advantages and novelties,and therefore,polyploid aquatic animals may possess excellent traits of economic interest including rapid growth,extensive adaptability and disease resistance.For this reason,numerous species of natural polyploid fishes,such as common carp,gibel carp,crucian carp,salmon,and sturgeon,were chosen as important target species for aquaculture.Many artificial polyploids have been commercially utilized for aquaculture and most of them were created from natural polyploid fishes of the Cyprinidae and Salmonidae.Thanks to the easy mass production and better economic traits in growth and flesh quality,the synthetized autopolyploids or allopolyploids from natural polyploid species in cyprinid fishes have been extensively applied to aquaculture throughout China.This review outlines polyploidy advantages and innovative opportunities,lists natural polyploid species used in aquaculture,and summarizes artificial polyploids that have been induced or synthetized,and used in aquaculture.Moreover,some main research trends on polyploid utilization and ploidy manipulation of aquaculture animals are also introduced and discussed in the review.

The occurrence,inheritance,and segregation of complex genomic structural variation in synthetic Brassica napus

"Synthetic"allopolyploids recreated by interspecific hybridization play an important role in providing novel genomic variation for crop improvement.Such synthetic allopolyploids often undergo rapid genomic structural variation(SV).However,how such SV arises,is inherited and fixed,and how it affects important traits,has rarely been comprehensively and quantitively studied in advanced generation synthetic lines.A better understanding of these processes will aid breeders in knowing how to best utilize synthetic allopolyploids in breeding programs.Here,we analyzed three genetic mapping populations(735 DH lines)derived from crosses between advanced synthetic and conventional Brassica napus(rapeseed)lines,using whole-genome sequencing to determine genome composition.We observed high tolerance of large structural variants,particularly toward the telomeres,and preferential selection for balanced homoeologous exchanges(duplication/deletion events between the A and C genomes resulting in retention of gene/chromosome dosage between homoeologous chromosome pairs),including stable events involving whole chromosomes("pseudoeuploidy").Given the experimental design(all three populations shared a common parent),we were able to observe that parental SV was regularly inherited,showed genetic hitchhiking effects on segregation,and was one of the major factors inducing adjacent novel and larger SV.Surprisingly,novel SV occurred at low frequencies with no significant impacts on observed fertility and yield-related traits in the advanced generation synthetic lines.However,incorporating genome-wide SV in linkage mapping explained significantly more genetic variance for traits.Our results provide a framework for detecting and understanding the occurrence and inheritance of genomic SV in breeding programs,and support the use of synthetic parents as an important source of novel trait variation.

Ploidy and fruit trait variation in oil-tea Camellia:Implications for ploidy breeding

Plant polyploidy often occurs in conjunction with higher yield and superior quality.Therefore,obtaining polyploid germplasms is a significant part of breeding.The oil-tea Camellia tree is an important native woody plant that produces high-quality edible oil and includes many species of Camellia with different ploidies.However,whether higher ploidy levels in oil-tea Camellia trees are related to better traits remains unclear.In this study,the ploidy levels of 30 different oil-tea Camellia strains in three different species in the Sect.Paracamellia were determined by flow cytometry and chromosome preparation,and the phenotypic characteristics and fatty acid compositions of the fruits were examined by field observations and laboratory analyses.The correlations between the ploidy level of oil-tea Camellia and the main traits of the fruit were investigated.Our results showed that 10 Camellia lanceoleosa strains were diploid,10 Camellia meiocarpa strains were tetraploid and 10 Camellia oleifera strains were hexaploid.Hexaploid C.oleifera had larger fruit size and weight,more seeds per fruit,greater seed weight per fruit,higher oil content and greater yield per crown width than tetraploid C.meiocarpa and diploid C.lanceoleosa,but their fruit peel thickness and fresh seed rate were significantly lower,and these traits were significantly correlated with ploidy level.In addition,in terms of fatty acid composition,hexaploid C.oleifera had a higher oleic acid content than tetraploid C.meiocarpa and diploid C.lanceoleosa,but their linoleic acid,linolenic acid and arachidonic acid contents were lower.The contents of palmitic acid,stearic acid and total unsaturated fatty acids were not significantly correlated with ploidy level.In conclusion,certain correlations exist between the main characteristics of oil-tea Camellia fruit and the ploidy level,and increasing the ploidy level led to an increase in fruit yield with no effect on oil composition.The discovery of variations in the main characteristics of oil-tea Camellia fruit with different ploidies will facilitate germplasm innovation and lay a foundation for ploidy breeding and mechanistic research on fruit traits.

Allotetraploidization event of Coptis chinensis shared by all Ranunculales

Coptis chinensis Franch.,also named Chinese goldthread is a member of Ranunculaceae in the order Ranunculales and represents an important lineage of early eudicots with traditional medicinal value.In our study,by using syntenic analysis combined with phylogenomic analysis of C.chinensis and four other representative genomes from basal and core eudicots,we confirmed that the WGD event in C.chinensis was shared by Aquilegia coerulea and Papaver somniferum L.and quickly occurred after Ranunculales diverged from other eudicots,likely a Ranunculales common tetraploidization(RCT).The synonymous nucleotide substitutions at synonymous sites distribution of syntenic blocks across these genomes showed that the evolutionary rate of the P.somniferum genome is faster than that of the C.chinensis genome by approximately 13.7%,possibly due to Papaveraceaes having an additional special tetraploidization event(PST).After Ks correction,the RCT dated to 115—130 million years ago(MYA),which was close to the divergence of Ranunculaceaes and Papaveraceaes approximately115.45—130.51 MYA.Moreover,we identified homologous genes related to polyploidization and speciation and constructed multiple sequence alignments with different reference genomes.Notably,the event-related subgenomes in the basal genomes all showed genomic fractionation bias,suggesting a likely allopolyploid nature of the RCT,PST and T-Alpha and T-Beta events in Tetracentron sinense.In addition,we detected that the sixteen P450 subfamilies were markedly expanded in the genomes of Ranunculales,and most of them were related to the RCT and PST events.We constructed a new platform for Early Eudicot Comparative Genomic Research(http://www.cgrpoee.top/index.html)to store more information.In summary,our findings support the WGD of C.chinensis shared by Ranunculales,which is likely an allotetraploidization event.This present effort offered new insights into the evolution of key polyploidization events and the genes related to secondary metabolites during the diversification of early eudicots.

A likely paleo-autotetraploidization event shaped the high conservation of Nyssaceae genome

Scientific knowledge about the ancestral genome of core eudicot plant kingdom can potentially have profound impacts on both basic and applied research,including evolution,genetics,genomics,ecology,agriculture,forestry,and global climate.To investigate which plant conserves best the core eudicots common ancestor genome,we compared Arcto-Tertiary relict Nyssaceae and 30 other eudicot plant families.The genomes of Davidia involucrata(a known living fossil),Camptotheca acuminata and Nyssa sinensis,one per existent genus of Nyssaceae,were performed comparative genomic analysis.We found that Nyssaceae originated from a single Nyssaceae common tetraploidization event(NCT)-autotetraploidization 28-31 Mya after the core eudicot common hexaploidization(ECH).We identified Nyssaceae orthologous and paralogous genes,determined its chromosomal evolutionary trajectory,and reconstructed the Nyssaceae most recent ancestor genome.D.involucrata genome contained the entire seven paleochromosomes and 17 ECH-generated eudicot common ancestor chromosomes and was the slowest in mutation among the analyzed 42 species of 31 plant families.Combing both its high retention of paleochromosomes and its low mutation rate,D.involucrata provides the best case in conservation of the core eudicot paleogenome.

Polyploidy Induction and Morphological Characteristics in the Asiatic Hybrid Lily(Lilium spp.cultivar dazzling)

The Asiatic hybrid lily cultivar Lilium dazzling(family Liliaceae)is a perennial herbaceous bulbous plant with bright yellow flowers of ornamental values.It also shows resistance to diseases and abiotic stress,making it an ideal parent for breeding studies.This study established a sterile culture system using scales of dazzling lily as explants to induce polyploidy.Adventitious buds growing to 1 cm were treated with different concentrations of colchicine(125,250 and 500μmol·L-1),pendimethalin or trifluralin(100,200 and 300μmol·L-1,respectively)for 12,24 and 36 h.Flow cytometry and chromosome counting were used to identify ploidy,and the phenotype of the polyploids was examined by stomatal observation and leaf index determination.With increasing mutagen concentration and exposure time,the mortality and mutagenic rate increased.The optimal treatment group was:300μmol·L-1 trifluralin for 12 h,which resulted in 15.55%mortality rate and 42.22%induction rate.The polyploid plants showed a significant increase in stomata length,leaf length and leaf width,with a decrease in stomatal density compared with the control plants.This study provided a basis for polyploid breeding.

Study on Genomic Changes in Partial Amphiploids of Common Wheat_Wheatgrass

According to conventional theory, little genomic changes should occur in homozygous and stable amphiploids of the grass family, particularly those involving polyploid wheat as a parent. In the present study, however, extensive genomic changes were detected in two octoploid partial amphiploids of common wheat (Triticum aestivum L.)_wheatgrass (Agropyron intermedium (Host) P.B.=Elytrigia intermedia (Host) Nevski=Thinopyrum intermedium (Host) Barkworth and Dewey), namely Zhong 3 and Zhong 5, by RFLP analysis using 10 low_copy, wheat chromosome_specific sequences and 33 representative homoeologous group_specific sequences as probes. Genomic changes involved loss of wheat hybridization fragment(s) and/or acquisition of new fragment(s). Uniformity of the RFLP patterns among 5 individual plants taken respectively from Zhong 3 and Zhong 5 in two successive generations, suggested that genomic changes probably had occurred in the early few generations after octoploid amphiploid formation, and remained essentially static thereafter. The highly similar RFLP patterns between Zhong 3 and Zhong 5, which had identical genomic constitution but differed from each other due to involvement of different wheat varieties as parents imply that genomic changes were probably not at random. Possible causes for the extensive and rapid genomic changes in the newly formed plant amphiploids, as well as their implications for polyploid genome evolution and breeding application are discussed.

Characterization of Two Groups of Low_copy and Specific DNA Sequences Isolated from Chromosome 7B of Common Wheat

Recent work revealed that, in the genomes of polyploid wheat, there exists a class of low_copy and chromosome_specific sequences that are labile upon polyploid formation. This class of sequences was proposed to play a critical role in the stabilization and establishment of nascent plant polyploids as new species. To further study this issue, five wheat chromosome 7B_specific sequences, isolated from common wheat (Triticum aestivum L.) by chromosome microdissection, were characterized. The sequences were studied by genomic Southern hybridizations on a collection of polyploid wheats and their diploid progenitors. Four sequences hybridized to all polyploid species, but at the diploid level to only species closely related to the B_genome of polyploid wheat. This indicates that these sequences originated with the divergence of the diploid species, and was then vertically transmitted to polyploids. One sequence hybridized to all species at both the diploid and polyploid levels, suggesting its elimination after the polyploid wheat formation. The hybridization of this sequence to two synthetic polyploid wheats indicated that sequence elimination is a rapid event and probably related to methylation status of the sequence. Based on the above results, we suggest that selective changes of low_copy sequences occur rapidly after polyploid formation, which may contribute to the differentiation of chromosomes in newly formed allopolyploid wheats.

Colchicine-induced Melilotus Research

[Objective] The aim was to identify the ploidy of sweet clover induced by colchicine. [Method] The sweet clover germinating seeds and colchicine solution were used for materials to research colchicine-induced Melilotus. [Result] The results showed that the concentration of 0.2% colchicine solution could induced double sweet clover which showed corresponding features of polyploidy plants as a whole showed great features. [Conclusion] Sweet clover induced by colchicine was polyploidy.

Study on the Polyploid Induction of Lycium ruthenicum Murr.

With apical leaves of Lycium ruthenicum Murr as experimental material, the polyploids of L. ruthenicum were induced with colchicine solution, and total four polyploidy plants were identified by chromosome courts. The results showed that tetraploid plants of L. ruthenicum were successfully induced with 300 mg/L of colchicine solution after 7 and 21 d of induction, with 400 mg/L of colchicine solution after 14 days of induction, and with 500 mg/L of colchicine solution after 7 days of induction, respectively.

Genome editing opens a new era of genetic improvement in polyploid crops

Sequence-specific nucleases(SSN) that generate double-stranded DNA breaks(DSBs) in genes of interest are the key to site-specific genome editing in plants. Genome editing has developed into one method of reducing undesirable traits in crops by the induction of knockout mutations. Different SSN-mediated genome-editing systems, including LAGLIDADG homing endonucleases or meganucleases, zinc-finger nucleases, transcription activator-like effector nucleases and clustered regularly interspaced short palindromic repeats, are emerging as robust tools for introducing functional mutations in polyploid crops including citrus, wheat, cotton, soybean, rapeseed, potato, grapes, Camelina sativa,dandelion, and tobacco. The approach utilizes knowledge of biological mechanisms for targeted induction of DSBs and their error-prone repair, allowing highly specific changes at designated genome loci. In this review, we briefly describe genome-editing technologies and their application to genetic improvement of polyploid crops.

Protection of Carassius auratus Gibelio against infection by Aeromonas hydrophila using specific immunoglobulins from hen egg yolk

Specific immunoglobulin (IgY) from egg yolk against Aeromonas hydrophila was produced by immunization of White Leghorn hens with formalin-killed whole cells of A. hydrophila. ELISA test using A. hydrophila as the coating antigen revealed that the specific antibody titer started to increase in the egg yolk at the 13th day post-immunization (P/N=2.18), reached the peak at the 56th day (P/N=13.82), and remained at high level until day 133 (P/N=7.03). The antibody was purified by saturated ammonium sulphate with a recovery rate of 63.5%. The specific IgY inhibited the growth of A. hydrophila at a concentration of 1.0 mg/ml during the 18 h incubation. Pre-treatment of polyploid gibel carps Carassius auratus Gibelio with specific IgY had a protection rate of 60% (6/10) against challenge with A. hydrophila, while none of the fishes in the control groups receiving sterile phosphate buffered saline (PBS) or non-specific IgY survived the challenge. Treatment of fishes with the specific IgY 4 h after the challenge also had lower mortality (70%, 7/10), a 30% reduction against the control PBS or non-specific IgY groups (10/10). These results indicate that specific IgY antibodies could be obtained easily from hens immunized with an inactivated A. hydrophila and could provide a novel alternative approach to control of diseases in fishes caused by this organism.

Analysis of cytosine methylation in early generations of resynthesized Brassica napus

DNA methylation, an important epigenetic modification, serves as a key function in the polyploidization of numerous crops. In this study, early generations of resynthesized Brassica napus （F1,S1-S3）, ancestral parents B. rapa and B. oleracea were analyzed to characterize their DNA methylation status during polyploidization, applying DNA methylation-sensitive amplifica- tion polymorphism （MSAP） and high-performance liquid chromatography methods. In F, 53.4% fragments were inherited from both A- and C-genomes. Besides, 5.04 and 8.87% fragments in F were inherited from A- and C- genome, respectively. 5.85 and 0.8% fragments were newly appeared and disappeared in resynthesized B. napus, respectively. 13.1% of these gene sites were identified with methylation changes in F, namely, hypermethylation （7.86%） and hypomethylation （5.24%）. The lowest methylation status was detected in F （38.7%） compared with in S1-S3. In S3, 40.32% genes were methylated according to MSAP analysis. Sequencing of methylated fragments indicated that genes involved in multiple biological processes were modified, including transcription factors, protein modification, and transporters. Expression ananlysis of DNA methyltransferase I and DNA methyltransferase chromomethylase 3 in different materials was consistent to the DNA methylation status. These results can generally facilitate dissection of how DNA methylation contributes to genetic stability and improvement of B. napus during polypLoidization.

Genomic footprints of wheat evolution in China reflected by a Wheat660K SNP array

Common wheat(Triticum aestiuum L.)is one of the most important crops because it provides about 20%of the total calories for humans.T.aestiuum is an excellent modern species for studying concerted evolution of sub-genomes in polyploid species,because of its large chromosome size and three well-known genome donors.Establishment of common wheat genome reference sequence and development of high-density SNP chips provide an excellent foundation to answer questions of wheat evolution and breeding at the genomic level.By genotyping more than 600 accessions of common wheat and their diploid and tetraploid ancestors using a Wheat660 K SNP array,we found dramatic genome changes due to tetraploidization and hexaploidization,in contrast to weaker influences of domestication and breeding on them.Further,since common wheat was introduced in China in 1500 BCE,Chinese landraces formed two subgroups(T.aestiuum-L1 and T.aestiuum-L2)with considerably diverse geographic distributions and agronomic traits.T.aestiuum-L2,mainly distributed in central and east China is found to have more but smaller oval grains with early maturity characteristics.We found that variation and selection in intergenic regions of the A and B sub-genomes dominated this differentiation,in which chromosomes 7 A and 3 B took the leading roles due to the existence of putative genes related to defense responses and environmental adaption in the highly differentiated regions.Large haplotype blocks were detected on 3 B(232.6-398.3 Mb)and 7 A(211.7-272.9 Mb)in the landraces,forming two distinct haplotypes,respectively.We discovered that artificial crosses in breeding promoted recombination in the whole genome,however,this recombination and differentiation was highly asymmetric among the three sub-genomes in homoeologous regions.In addition,we found that the wide use of European and northern American cultivars in breeding at early era,led dramatic changes in Chinese wheat genome,whereas,the recent breeding functioned to optimize it.This study will provide the insight for reconsideration of wheat evolution and breeding,and a new strategy for parent selection in breeding.

Karyotype and cytogeography of the genus Heracleum (Apiaceae) in the Hengduan Mountains

In the present study, the karyotypes of 34 populations belonging to 11 species and one variety of Heracleum from the Hengduan Mountains in China were examined. Chromosome numbers and the karyotypes of three species （H. souliei, H. la＇ngdoni, and H. wenchuanense） are reported for the first time, as are the karyotypes of H. moellendorffii and H. henryi （tetraploid）. Populations of H. candicans, H. franchetii, and H. kingdoni in the Hengduan Mountains were found to consist of a mixture of diploid and tetraploid plants. Except for four species of Heracleum, namely H. candicans, H. franchetii, H. henryi, and H.kingdoni, which have both diploid and tetraploid karyotypes, all other species of Heracleum are were found to be diploid. All karyotypes were found to belong to the 2A type of Stebbins, with the exception ofH. candicans var. obtusifolium, which belongs to 2B, and H. hemsleyanum and H. franchetii （Mt. Dujuan, Daocheng, Sichuan, China）, which belong to 1A. There was only a slight difference in the karyotype asymmetry index, which suggests a close kinship for species of Heracleum and that the entire phylogenetic development of Heracleum is relatively primitive. Species that exhibited advanced morphological features were also more advanced in karyotype structure, with the order ofkaryotype evolution being 1A→2A→2B. This phenomenon indicates that the species distributed in the Hengduan Mountains have not diverged completely and that the Hengduan Mountains are a relatively young and active area for the evolution of Heracleum. Polyploidization in Heracleum may be an important evolutionary mechanisms for some species, generating diversity. The biological attributes, distribution range, and the geological history of the genus have all played a part in accelerating the evolution through polyploidization or aneuploidization. It is known that as the distribution latitude of Heracleum decreases from north to south, the chromosome number, ploidy level, and asymmetry structure appear to increase. In the Hengduan Mountains, these tendencies are also evident. Finally, based on all the available cytogeographic data, we speculate that the more advanced tetraplont or aneuploid species of Heracleum in India may be derived from early diplont species that were distributed in the Caucasus region and Hengduan Mountains. The dispersal of Heracleum was from Eurasia to India, because this correlates with the emergence of the Himalayan Mountains through tectonic movement. Thus, the Hengduan Mountains are not only a center of diversity for Heracleurn, but also a center of active speciation in modern times.

Mechanisms involved in selecting and maintaining neuroblastoma cancer stem cell populations, and perspectives for therapeutic targeting

Pediatric neuroblastomas(NBs)are heterogeneous,aggressive,therapy-resistant embryonal tumours that originate from cells of neural crest(NC)origin and in particular neuroblasts committed to the sympathoadrenal progenitor cell lineage.Therapeutic resistance,post-therapeutic relapse and subsequent metastatic NB progression are driven primarily by cancer stem cell(CSC)-like subpopulations,which through their self-renewing capacity,intermittent and slow cell cycles,drug-resistant and reversibly adaptive plastic phenotypes,represent the most important obstacle to improving therapeutic outcomes in unfavourable NBs.In this review,dedicated to NB CSCs and the prospects for their therapeutic eradication,we initiate with brief descriptions of the unique transient vertebrate embryonic NC structure and salient molecular protagonists involved NC induction,specification,epithelial to mesenchymal transition and migratory behaviour,in order to familiarise the reader with the embryonic cellular and molecular origins and background to NB.We follow this by introducing NB and the potential NC-derived stem/progenitor cell origins of NBs,before providing a comprehensive review of the salient molecules,signalling pathways,mechanisms,tumour microenvironmental and therapeutic conditions involved in promoting,selecting and maintaining NB CSC subpopulations,and that underpin their therapy-resistant,self-renewing metastatic behaviour.Finally,we review potential therapeutic strategies and future prospects for targeting and eradication of these bastions of NB therapeutic resistance,post-therapeutic relapse and metastatic progression.

Cross Breeding of Populus and Its Hybrids for Cold Resistance

Populus tomentosa was crossed with P.tremuloidis, P.grandidentata, P.alba×P.grandidentata and P.alba×Ulmuspumila in order to maintain its rapid growth and high wood quality and improve its resistance to cold. Two methods were used to increase the germination rate from 1.5% to 41.1% and the remaining rate from 1.7% to 44.2%. Forty crossing combinations were conducted and 2744 hybrid seedlings were obtained. MX4×P.grandidentata （G-1-58）, MX3×P.tremuloidis （T-44-60）, MX2×P.tremuloidis （1-13-87-37） and MX2×（P.alba×P.grandidentata） were regarded as superior combinations after analysis and selection. Thirty seedlings of these combinations and 11 triploid seedlings identified by counting their chromosomes were selected as super plants.