| This research with Populus deltoides divided into four portions.It included: parent selection,cross experiment,analysis of cross-breeding progenies,genetic variation analysis and family selection of hybrid progeny population from T120 and I-69.Through analyzing genetic variation of clones in germ-plasm pool on six traits including height(h),diameter at breast height,volume,average wood density, heartwood density,sap-wood density,it showed that the variation coefficient and the range of provenance D and familly 81,86,88,89,93,94,95,96,100,102,103 were greater than others.It was significant difference among clones in every trait at 0.01 level.The generalized heritability of height(0.32) was lower than other traits(0.53-0.8).Based on clones level and considering index heritability,correlation coefficient with ideal-genotype and expected selection development ,the author constructed the comprehensive selection index as follows: I = -0.060312h+1.7357965d-0.970367v+0.4159484pm+0.189431xm+0.6429274bmThis index had the best expected selection development(2.88),also its heritability and correlation coefficient with ideal-genotype were better than other indexes relatively.According to the index and observation in the field,parents were selected as follows:female parents were 74-4,86-10,81-22,66-9,94-12,94-30,86-8,40-1 and T2;male parents were 95-44,86-2,89-2,81-16,89-3,45-1,96-10,102-14,3101,3412,3804,3244,3239,3229 and 3415.This paper registered the process of cross experiment detailedly and summarized the precautions in hybridization technology.176 combinations(8(female)×22(male)) were planned by NCⅡm ating design in the experiment.There were 41 combinations and 3,900 hybrids when were being transplanted.Female parents 74-4 and 86-10 obtained more combinations and hybrids,but 40-1,81-22 and 86-8 got nothing.The bad weather,unenough prepared work,low pollen viability, the repeat and time of pollination were the main reasons for the unsuccessful result.The analysis of combining ability and genetic variation was applied on the obtained combinations.Female 74-4 and male 3244 has the best general combining ability. The GCA value of the ground diameter and height was 0.07(74-4),0.05(3244) and 7.83(74-4),6.67(3244) respectively.The combination of 74-4×3244 had the best special combining ability.The SCA value of the ground diameter and height was 0.18 and 19.11 respectively.The genetic variation analysis of hybrids used the method of nest design.The result of variance analysis and multiple comparison on the ground diameter and height showed that there was significant difference at 0.01 level among parents and female 94-30,74-4 were better than others. In addition,5-year-old hybrids from 10 cross-combinations were used as test material.The genetic variation of height,diameter at breast height and volume were measured and analysed.The result showed that a significant variance was observed in 3 traits.The variation coefficient at these 3 traits had a sequence as follows:volume>diameter>height.Family heritability which was belong to higher genetic level(0.8-0.82) was stronger than single-tree heritability which was belong to weaker genetic level(0.25-0.29).Superior family No.6 and No.4 were selected with the method of Dunnett's One-tailed t Tests.Genetic gain of height,diameter at breast height and volume were 2.8%,3.1% and 8.5% respectively.
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