Genetic Variation And Its Physiology In F₁ Hybrids Of Eucalyptus Urophylla × E.camaldulensis By A Reciprocal Mating Design

Eucalypts,a very important economic tree species,is extensively cultivated in southern China,in which,Eucalyptus urophylla(U),E.grandis and their hybrid clones are the two most extensively cultivated species due to their fast growth rate,good stem-form and superior adaptability.However,in southern China,a main eucalyptus plantation area,U,E.grandis and their hybrid clones have been faced with a huge threat of monsoon and typhoon,and the survival is less than 20% in severe cases,which resulting in a serious decline in wood production.Therefore,breeding and selecting of wind resistance genotype is already imminent.An inter-specific F1 hybrid breeding program involving U and E.camaldulensis(C)was implemented in 2007 in order to provide genotypes better adapted to southern China with improved growth rate,stem straightness and wind resistance.A trial involving 36 reciprocal factorial mating design crosses from six parents each of C and U that had been preselected for superior growth and stem straightness was assessed.Ten open-pollinated(OP),pure-species families using the hybrid parents as females were included as controls,and the early growth rate had been inverstigated in the junenile stage.Based on the previous studies,the U×C interspecific F1 hybrids with OP controls at age of 9-year-old were used as the materials,the genetic variation and heterosis in terms of growth traits,stem form and wood property were analyzed,the differences of leaf morphology,photosynthetic pigment content and mineral nutrient content of different combinations and families were also comparied.Trait-trait genetic correlations were also estimated amongst leaves morphological trait,photosynthetic pigments content,mineral nutrient elements content and growth traits in different combinations and families to reveal the physiological genetics of genetic variation and heterosis of U×C F1 hybrids from morphological and physiological perspectives.These results will provide a theoretical basis for the prediction and utilization of eucalyptus heterosis,selection of parent and hybrid progeny,and development and utilization of wood,and finally provide thetheoretical basis for the development of hybrid breeding strategy and superior veriety breeding program.The main findings are as follows:(1)Inter-specific hybrids generally performed better than the pure species in terms of survival and growth traits.Female U by male C crosses generally outperformed those involving male U and female C for growth traits.Further indication of the significant reciprocal effect was supported by negative and low correlations between paired groups of full-sibs that differed only in the direction of the cross.Components of female additive genetic variance(?2A)and single-tree's(h2S)and family's(h2F)narrow-sense heritability calculated from this estimate(?2Af and h2f)were generally higher than those of the male(?2Am,h2m),providing evidence for maternal effects,the h2 S and h2 F tended a trend of h2m>h2>h2f.The h2 S estimates based on general hybridizing ability for growth traits were generally low at both ages,whilst,the h2 F were generally high to moderate at age of 2 years,and generally low and of low precision at 8.3 years.The ratio of hybrid dominance to additive variance(?2D/?2A)increased with age,additive genetic effect is the main contributor in juvenile stage,and the dominant effect is the main contributor in mature stage,being of little practical consequence at age 2years.Trait-trait genetic correlations amongst hybrids were generally positive and moderate to high.Hybrid vigour,gauged by comparison with the performance of the pure species progeny was significant.(2)Inter-specific hybrids generally performed better than the pure species in terms of stem straightness(STR),crown width(CR)and first branch height(FBH),the results showed that these three traits had significant heterosis.Female U by male C crosses generally outperformed those involving male U and female C for 4 stem form traits.Further indication of the significant reciprocal effect was supported by negative and low correlations between paired groups of full-sibs that differed only in the direction of the cross,which were consistent with growth traits.The parental effect varied from mating direction in terms of 4 stem form traits.In terms of STR,branching(BR)and CR,the maternal effect was generally lower than that of paternal effect in female U by male C crosses,whilst,the maternal effect was generally higher than paternal effect in female C by male U crosses.The h2 S was generally low,indicating that 4stem form traits were of low genetic control,whilst,the h2 F was generally high to moderate and of low precision.The h2 S and h2 F tended to be the trend of h2 f > h2 > h2 m in female C by male U crosses,and the trend of h2 m >h2 > h2 f in female U by male C crosses.The ?2D/?2A ratio of hybrids also varied from mating direction,which was larger than 1 in female U by male C crosses,and smaller than 1 in female C by male U crosses.Trait-trait genetic correlations amongst hybrids between STR,BR and FBH were generally significantly positive,and significantly negative between CR and STR,BR.However,Trait-trait genetic correlations between stem form and growth traits were significantly positive,indicating that STR,BR,FBH,HT,and DBH can be improved feasibility at the same time.(3)Inter-specific hybrids generally performed better than the pure species in terms of basic density(BD),fibre width(FW)and ratio of fibre lenth to fibre width(FL/FW).Female C by male U crosses generally outperformed those involving male C and female U in terms of BD and FW.Maternal effects were generally lower than those paternal effects in female U by male C crosses,and generally higher than the paternal effects in female C by male U crosses.The ?2D /?2A ratio of hybrid were generally larger than 1 for BD,FL and FW in reciprocal crosses.The h2 S was generally low,whilst,h2 F was generally high to weak and of low precision.The h2 S and h2 F tended to be the trend of h2 m > h2 > h2 f in female U by male C crosses in terms of BD,FL and FL/FW,and tended to be the trend of h2 f > h2 > h2 m in female C by male U crosses.Trait-trait genetic correlations amongst hybrids between BD and fibre traits were generally negative,and positive between fibre traits.However,Trait-trait genetic correlations between BD and growth traits were positive,as well as those between FL and growth traits.(4)In terms of leaf morphological traits,rich genetic diversity showed in control pollinated hybrids and open pollinated progeny,especially in control pollinated progenies.Leaf morphological differences were significant mainly due to tree species,not significant at the level of family and individual plants.The leaf length(LL),ratio of LL to leaf width(LW),fresh weight of single leaf(LFW),dry weight of single leaf(LDW)and ratio of leaf weight(LSD)for C were significantly lower than those of U,C×U,U×C,a trend of U>C×U,U×C>C was tended in LL,LL/LW and LDW,in terms of LW,C was significantly greater than those of U,C×U and U×C.A negative heterosis was found in all crosses in terms of LW,whilst,positive heterosis was found in the other six morphological traits.In terms of LL and LL/LW,heterosis was more significant in female C by male U crosses than that of female U by male C crosses.The heterosis in female U by male C crosses was more obvious for leaf area(LA),single leaf fresh weight(FLW),dry weight of single leaf(DLW)and LSD.Trait-trait Pearson correlations were significantly positive amongst leaf morphological traits,and also between LSD and DBH increasing rate,LW and volume increasing rate.(5)The content of photosynthetic pigments in interspecific CP hybrids and OP progeny was significantly different amongst 4 populations and 82 families in terms of chlorophyll a(Ca),chlorophyll b(Cb),Cab and carotenoid(Ck).The variation coefficiance was larger in control pollinated hybrid progeny than that in open pollinated,especially female U by male C crosses.The contents Ca,Cb,Cab and Ck of U,C×U and U×C were higher than those of C,and in terms of ratio of Ca/Cb,C was significantly higher than that of U,C×U and U×C.The heterosis was found in terms of Ca,Cb,Cab and Ck in C×U and U×C F1 hybrids,which was especially significant in U×C F1 hybrids.Trait-trait Pearson correlations amongst photosynthetic pigment content were significantly positive,whilst,which were significantly negative between photosynthetic pigment content and LA,FLW,DLW.(6)The relative contents of N,P,K for 72 interspecific hybrids were 3.070,2.98 and 5.933,respectively,and the variation ranges in terms of N,P,K were 3.736~2.587,4.9~0.573,8.333~2.391,respectively.The contents of N and P of female U by male C crosses were significantly higher than those of in female C by male U crosses,and also a trend of U×C>C×U tended in K.Trait-trait Pearson correlations between N and P,N and K,N and four photosynthetic pigments traits were significantly positive,whilst,which were generally significantly negative between nutrient content and FLW,DLW,DLW.