Preliminary Study On The Effects Of Heterosis Based On Differences Of Genome Size In Brassica Napus L.

Heterosis is an effective way to improve crop yield,resistance and quality by utilizing genetic differences between parents.Brassica napus L.is a successful crop for utilization of heterosis after rice.A large number of scholars have long been devoted to studying the inheritance of rapeseed heterosis in order to make better use of heterosis on genetic basis and prediction methods.However,the contribution of differences in genome size between parents to effects of heterosis is unclear.In the early stage of the study,the size of the parental genome of 10 Brassica napus L.was detected by flow cytometry.These 10 materials were assigned 24 hybrid progenys by positive and negative crossover according to the difference in genome size.The effects of differences in genome size between parents on the heterosis of rapeseed were analyzed by flow cytometry,SSR identification,SNP molecular markers and MSAP.The main findings showed as follows:1.The results of genome size detection by parental flow cytometry showed that the genome size of 8 tetraploid materials ranged from 830.73 Mb to 924.00 Mb,and Y3560 and Y3380 were two octoploid materials with genome size of 1566.70 Mb and 1458.68 respectively.Ten parents were used to prepare 24 combinations of positive and negative crosses,and the true and false hybrids were screened by SSR molecular markers.The genome size of the hybrids was determined and found that the size of the hybrid F1 genome was larger than the genome size of the corresponding parents by flow cytometry.The genome size of the hybrids generally showed that the increase in the size of the maternal genome was smaller than that of the paternal genome,except for the two octoploid Y3560 and Y3380 recursive F1 generation ZJ24,and ZS11 and Y3560 orthogonal F1 generation ZJ7.Correlation analysis showed that the size of the hybrid F1 genome was significantly positively correlated with the parental genome size,and significantly positively correlated with the parental genome size.The hybrid F1 generation was Significantly negative correlation compared with the increase in the size of the maternal genome.2.Using the rapeseed 6K SNP chip to genotype 10 parents and hybrid F1 generation,and using the obtained SNP locus to estimate Nei genetic distance.The average genetic distance of 10 parents was 0.265,and the genetic distance between parents was0.052~0.369.The average genetic distance between the F1 generations and the male parents(0.308)is greater than the average distance between the F1 generations and the female parents(0.286).Correlation analysis between genome size and genetic distance revealed that there was no correlation between the genetic distance between the parents and the difference in genome size between the parents.3.From the MSAP technology detection results of genomic DNA methylation status,the total methylation level of parents and F1 generations ranged from 33.72% to 56.38%,and the average total methylation level between parents was higher than that of F1 generations.The correlation between genome size and methylation level showed that the genome size was significantly negatively correlated with total methylation level,hemimethylation level and total methylation level,and was significantly positively correlated with the level of methylation.4.Correlation analysis between genome size and traits showed that the genome size was significantly positively correlated with plant height,branch height and yield per plant,and was significantly negatively correlated with protein content.Further correlation analysis of the difference in genome size between hybrid parents and heterosis of F1 traits revealed that there is significant effect on plant height,height of branching,number of effective branches,1000-grain weight,number of fruit per pod,glucosinolate and potein of Mid-parent heterosis(or Over-parent heterosis)in traits of F1 generations.The correlation between the genetic distance between parents and the heterosis of F1 traits showed that the genetic distance between parents was only significantly related to roots,the 1000-grain weight,number of fruit per pod,and yield traits per plant of Mid-parent heterosis(or Over-parent heterosis)in traits of F1 generations.In addition,Correlation analysis DNA methylation level and traits performance of F1 generations can be seen that methylation level significantly correlated with plant height,branch height,main sequence solid section,whole plant effective pod,erucic acid,glucosinolate,oil content and protein.