| The hybrid is superior to its homozygous parent in comprehensive traits.Since the hybrid appears,the crop has been greatly increased,and some problems of food shortage and food safety have been solved.Although heterosis has been widely used in plants,its genetic mechanism has been vague.Based on previous studies,genome size differences exist among homoploidy materials and genome size is related to heterosis to some extent.In order to further explore the relationship between genome size and heterosis,this study selected materials on the same genetic basis of homoploidy to carry out research.In this experiment,the DH inducer line of rapeseed was used to induce cytoplasm male sterility three-line hybrid Rongyou 18 to get induced offspring.The genome size and ploidy were determined by flow cytometry and cytological observation.At the same time,removing off-type and selecting fertility plants by identifing of phenotypic fertility and restoring gene molecular marker.Then SNP chip detection was used to identify and verify the homozygosity of induced progeny in different lines and the genetic relationship between induced progeny and Rongyou 18,Rongyou 18 paternity C2970,Rongyou 18 maternal parent 0068A and induced line Y3380.The homozygosity and genetic relationship were in line with expectations.The induced progeny was hybridized with the female parent 0068A of Rong you 18 to obtain F1,and F1was detected by flow cytometry.Investigating F1traits with Rong you 18 as control,and conducting the correlation analysis of genome size,genetic distance and over-standard heterosis of phenotypic traits.At the same time,F1with high and low yield was selected for resequencing,and SNP site differences and distribution on chromosomes were analyzed.To further explore the specific association between genome size and yield heterosis,and analyze the strong heterosis and weak heterosis,as well as the distribution of SNP sites on the chromosome,in order to provide a new perspective for the utilization of heterosis in rapeseed.1.Flow cytometry was used to detect the genome size of the induced progeny which came from Rongyou 18.The relative genome size of the induced progeny varied from781.26 Mb to 977.28 Mb,and the variation range was 0 to 20%.2.Cytological observation of some induced progeny showed that the number of chromosomes 3689-26,which had the highest fluorescence value in G1 phase,was 2n≈52,belonging to hexaploid,while the number of chromosomes of other induced progeny was2n=38,which was tetraploid.Tetraploid mitotic chromosomes behave normally,while hexaploid meiosis chromosomes behave backward.3.Using pol CMS restoring gene molecular markers to identify induced offspring,56induced offspring containing restoration gene markers were obtained,and field fertility identification was conducted,and all were found to be fertile.Using the sterile plant as a control,it was found that the petals of the fertile plant were slightly larger,the pollen was plump and active,and the stamens were normal,which was consistent with the results of molecular marker identification of the restoring gene.4.The SNP chip detection of the induced progeny lines showed that the homozygosity was higher than that of rongyou 18.In the cluster analysis,it was found that the induced progeny clustered in three branches of C2970,0068A and ryou18,and the induced line were in a single branch,and the genetic distance between the induced progeny lines and the two parents（C2970,0068A）was smaller than that between C2970 and 0068A.These results indicated that these induced progeny were derived from hybrids with C2970 and0068A.5.As the male parent,the induced offspring lines to cross with 0068A,and 54 F1hybrids were harvested.The genome size of these F1was tested,and the results showed that the positive proportions of the increase in genome size from the mother,the increase in genome size from the father,and the mid-parent heterosis were 45.10%,39.22%,45.10%,respectively.Compared to the parents,only a portion of the hybrid F1genome size increases,which is greater than the values of the parents and middle parents.6.The over-standard heterosis of each trait of hybrid F1was calculated with the Rong you 18 as the control.It was found that the over-standard heterosis of each trait of hybrid F1showed significant over-standard heterosis,such as rootstock diameter,fruiting length of main branch,number of primary effective branch,number of effective silique and theoretical yield per plant,among which the over-standard heterosis of average theoretical yield per plant was the maximal,and the over-standard heterosis of actual yield in the plot was the minimum.7.The correlation analysis of genome size and genetic distance showed that there was no correlation between genome size of the hybrid offspring,the paternal genome size,the growth percentage in genome size of the hybrid offspring compared with the male parent and parental genetic distance.The correlation analysis of genome size,genetic distance and the over-standard heterosis of traits showed that the correlation coefficient between the genome size of male parent and over-standard thousand of seed weight was-0.310*,showing a significant negative correlation.The correlation coefficient between the growth percentage in genome size of the hybrid offspring compared with the male parent and the over-standard heterosis of thousand seed weight and yield in the plot was 0.300*and0.326*,respectively,showing a significant positive correlation.At the same time,the correlation coefficient between parental genetic distance and over-standard heterosis of rootstock diameter was 0.346*,which showed a significant positive correlation,and that between genetic distance and over-standard heterosis of thousand seed weight was-0.325*,which showed a significant negative correlation.8.With Rong you 18 as the control,Rongyou 18 parents,and 4 high-yield and 3low-yield F1which induced progeny crossed with the female parent 0068A for resequencing,and the differences of high-yield and low-yield SNP sites and their distribution on chromosomes were analyzed.It was found that high-yield and low-yield SNP sites were more distributed on chromosome A,and high-yield SNP sites were more distributed on chromosome A06 and C04.The low-yielding SNP sites were mainly distributed in A01,A03,A09 and C03,C04,C06,C08.These results indicated that the yield heterosis of chromosome A and chromosome C04 was relatively strong in the same genetic background. |
