Studies On Heterosis And Cytological Characters Of F₁ Between Viola Wittrockiana And Viola Cornuta

Viola wittrockiana and Viola cornuta are important early spring flowers and are known in Europe as queens of flower beds.Due to trade secrets of foreign breeding companies,the research about the mechanism of heterosis pansy is rarely reported.Ten kinds of V.wittrockiana and one kind of V.cornuta were used as experiment materials to cross hybridization to provide phenotypic and cytological references for hybrid heterosis breeding.A crossbreeding test was conducted to investigate the 12 main ornamental traits of the parents and the F₁ hybrids.The genetic differences between the parents based on the phenotype and the heterosis of the F₁generation were investigated.The cytological studies were performed using apical regular tableting,flow cytometry and stomatal measurement,results as following:1.The experiment studied and analyzed the 12 ornamental characters of 11 different inbred lines of V.wittrockiana and V.cornuta.The results showed that all the characters except for flower diameter and leaf thickness presented negative heterosis.With the flower diameter and number of flowers as breeding targets,1×10,3×1,7×9,11×3,10×9,11×10 hybrid combinations should be selected.2.The results of ploidy analysis of 11 pansy inbred lines and 30 F₁ hybrids by flowcytometry were as follows:The No.1 inbred line was diploid among 11 copies of the parents;the number of tetraploid were 10,they were 2¹1 inbred line.Among the 30 hybrids,there were 3tirploid,1×10,2×1,8×1;the number of tetraploid were 27,which mainly included 3×5,3×7,3×8,4×5,4×6,4×7,4×8,4×9,4×10,4×11,5×4,5×7,5×8,5×10,6×5,6×7,7×10,8×2,8×4,8×5,9×4,9×8,10×3,10×4,10×7,10×8,11×7.3.Statistics of 11 parental inbred lines of stomatal characteristics,the results showed that the stomatal length,width,density can be used as a indicators of ploidy identification in pansy.4.The result of root tip compression was consistent with the result of flow cytometry:chromosome number in V.cornuta was 26,karyotype formula was 2n=2x=26=8m+12sm+6st;The number of chromosomes in 10 V.wittrockiana ranges from 44 to 48.Their karyotype formula were2n=4x=48=16m+20sm+16st;2n=4x=48=36sm+12st;2n=4x=46=16m+32sm;2n=4x=46=12m+32sm+4st;2n=4x=44=16m+24sm+4st;2n=4x=48=32sm+16st;2n=4x=48=44sm+4m;2n=4x=48=8m+20sm+20st;2n=4x=48=4m+36sm+8st;2n=4x=44=4m+16sm+6s,and their karyotype were classed into 2B,3B.The chromosome counting of 74 F₁ hybrids results:the number of chromosomes ranges from 34 to 48;among 12hybrid F₁ karyotype analysis results:V.wittrockiana×V.cornuta（diploid×tetraploid,tetraploid×diploid）produced 6 triploid and 2 tetraploids;the progeny of V.wittrockiana intraspecific hybridization（tetraploid×tetraploid）were all tetraploid.The index of karyotypic asymmetry of all F₁ hybrids was 62.78%⁶7.39%,and their karyotype were classed into 2A,2B,3B.5.The fluorescence in situ hybridization system was preliminary established,and found that five pairs of 5S rDNA signals were detected in metaphases chromosome in JB-1-1-2;there were only four 5S rDNA signals on DFM-16-1-1,and the signals were all located at the end of the short arm of the chromosomes.