| Poplar has strong fast-growing,good wood,strong resistance and wide adaptability,and has become an important fast-growing industrial timber tree species in China.Among them,Populus deltoides is the main parental source of poplar breeding,and occupies an irreplaceable position in the cultivation of poplar high-yield plantations.Through the comprehensive evaluation and selection of multi-characteristics of P.deltoides clones in different site environments,the formation and regulation mechanism of poplar clones with different growth rates are further analyzed,which is of great significance for the genetic improvement and selective breeding of poplar.In order to breed excellent P.deltoides clones adapted to different experimental areas,we used 38 P.deltoides clones to build regional test forests in Rizhao,Shanxian and Boxing respectively.Genetic variation analysis,correlation analysis,multi-trait comprehensive evaluation and regional analysis of growth traits,stemform quality,disease and pests of 1-,2-and 5-year-old P.deltoides clone.To explore the transcriptional regulatory mechanisms and key genes that control poplar rapid growth,we further performed transcriptome sequencing of the cambium of three poplar clones with significantly different growth rates.The main results were as follows:（1）The phenotypic variation coefficient and genetic variation coefficient of growth traits of the 1-,2-,and 5-year-old P.deltoides clones in the three sites were 8.8%～73.6%,4.5%～33.7%,among which the volume was the largest,the diameter at breast height was the second,and the height was the smallest.The repeatability of growth traits were 0.40～0.96,among which height was the largest,followed by volume,and DBH was the smallest.There were significant or extremely significant differences in growth traits and form-quality traits between sites,between clones,interaction between location and clone.Overall,growth traits were positively correlated with number of branches,density of branches and leaves,defoliation time,stem taper and stem form,and negatively correlated with branch angle,branch thickness and bark split.The above results show that the P.deltoides clones have abundant genetic variation,the performance of traits is mainly affected by genetic factors,and there is a strong correlation between growth traits and form-quality traits,and the excellent clones screened from them can be stably inherited.（2）The combined membership function method and principal component analysis method were used to comprehensively evaluate the growth traits and stem-form quality of the 5-yearold P.deltoides clones in the three sites,and further selected the superior clones according to the resistance to pests and diseases of each clone.The top three clones with better performance of each trait in Rizhao were 5143,862 and 13-16.The top three clones with better performance of each trait in Shanxian were 862,5143 and 9253.The top three clones with better performance of each trait in Boxing were 4156,294 and 21-11.2158,7132 and4135 all performed well in the three sites and could be screened as excellent clones.The height in the GGE biplot was more reliable than the DBH,and the 2158,4135,and 7132 clones had strong high yield and stability.Shanxian had the best strength and representativeness,and was the most suitable test site for P.deltoides clones.（3）The numbers of differential genes in the three comparison groups with different growth rates（4156 vs 862,I-107 vs 4156,I-107 vs 862）were 4753,3766 and 2696,respectively.The functional analysis of differential genes of GO,COG and KEGG was mainly enriched in transcription Regulation,protein translation and modification,cell division and elongation,secondary cell wall synthesis,signal transduction,carbohydrate metabolism and energy conversion,etc.,indicate that the cambium of poplar clones with higher growth rates organizes cell activity,material transport and Metabolic activity is more intense.（4）I-107 vs 4156,I-107 vs 862,4156 vs 862 comparison groups accounted for 5.33%,5.57% and 6.04% of the number of differential genes in the annotation files,respectively.The transcription factors in the I-107 vs 4156 and I-107 vs 862 comparison groups were mainly involved in the regulation of cell differentiation,phytohormone synthesis and signal transduction,photomorphogenesis and signal response,regulation of stomatal movement,and regulation of plant organ development.Transcription factors in the 4156 vs 862 control group were mainly involved in the regulation of cell division and differentiation,phytohormone synthesis and signal transduction,cambium,phloem and xylem histogenesis.（5）Eighteen genes in the three control groups were up-regulated,mainly involved in catalytic activity,signal transduction,carbohydrate transport and metabolism,etc.Among the three comparison groups,14 genes were down-regulated,mainly involved in RNA processing and modification,signal transduction,plant defense response,and synthesis,transport and decomposition of secondary metabolites.In the I-107 vs 4156 and I-107 vs 862 comparison groups,24 differential genes were specifically up-regulated and 33 differential genes were specifically down-regulated,indicating that Populusxeuramericana ?Neva? with the highest growth rate was different from P.deltoides ?4156? and P.deltoides ?862? with lower growth rates.There are some differences in the transcriptional regulation mechanism.Further analysis of common differential genes found that poplar may affect its growth rate by regulating cell cycle,leaf morphology and senescence,hormone synthesis and response,plant cell wall chemical synthesis,growth stage transition and response to biotic and abiotic stresses..In conclusion,this study conducted a comprehensive multi-character evaluation of the 5-year-old P.deltoides clones,and screened out clones 2158,7132 and 4135 with high yield and stability.Poplar clones with different growth rates had certain differences in the regulation of cell cycle,leaf senescence,hormone synthesis and response,cell wall chemical synthesis and growth stage transition.These studies can improve the reference of poplar genetic improvement and selective breeding. |
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