Combining Ability,Heterosis And Heterosis Grouping Analysis Between Chinese Semiwinter And Exotic Winter And Spring Lines Of Rapeseed (Brassica Napus L.)

Rapeseed(Brassica napus L.)is an important edible oilseed crop in the world.Rapeseed oil is used for human consumption and industries,and the meal is used as animal feed.The production of rapeseed has expanded remarkably in most of the major rapeseed growing countries.China,Canada,and European countries lead the world in rapeseed production.In China rapeseed is an important oilseed crop with annual production amounting to 14.5 metric tonnes.Improvement in yield,oil content,and oil quality are important objectives of rapeseed breeding programs.Heterosis and combining ability are two important and well known prospects to develop new and high yielding varieties.Earlier studies conducted to date revealed that genetic diversity is the base of heterosis,and the association between heterosis and genetic distance should be studied for proper utilization of heterosis.So far,in rapeseed,few studies have been conducted on heterotic patterns and heterotic groups.Therefore,present study was designed to study genetic diversity,heterosis,combining ability,heterotic patterns and heterotic groups among Chinese semi-winter type testers and exotic winter and spring type rapeseed lines.In this study,14 exotic lines(spring and winter types)and four testers(semi-winter type)of rapeseed(B.napus)were crossed in line × tester fashion to estimate heterosis,general and specific combining ability,and genetic distance for seed yield,yield components,and oil content.The F1 hybrids and their parents were evaluated for three consecutive seasons(2010/2011,2011/2012 and 2014/2015)at four locations in Northern China.All 18 parent lines were genotyped using simple sequence repeat(SSR)and sequence-related amplified polymorphism(SRAP)technique.The important results are obtained as follows;1.Heterosis and Combining ability analysis across locations in Chinese semi-winter × exotic lines of rapeseed(B.napus)In this study,results showed that highly significant(p ? 0.01)differences were observed among the parents and hybrids for all the traits across locations.Plant height,setting position of first primary branch and length of terminal raceme were controlled by additive genes,and number of branches,number of siliques on terminal raceme,number of siliques per plant,number of seeds per silique,seed yield per plant,1000-seed weight,oil content,and seed yield were controlled by non-additive gene action.The parental lines SP-Armada,9E49,and CZ25 and the tester Zhong9 proved to be good general combiners for seed yield.Among 56 F1 hybrids,four hybrids Zhong9 × CZ25,GZ1 R × 9E38,Zhong7 × 9E38,and Zhong7 × CZ49 out yielded than the check(Qinyou No.7)and were proved the outstanding combinations for seed yield.For oil content,12 hybrids Zhong7 × CZ25,Zhong7 × Profit,Zhong7 × CZ04,SH11 × 9E45,GZ1 R × CZ04,Zhong7 × CZ02,GZ1 R × CZ49,Zhong9 × Excell,Zhong9 × CZ02,SH11 × CZ49,GZ1 R × Profit,and Zhong7 × SP-Armada were found best hybrid combinations.These hybrids are recommended to be included in future breeding programmes for development of new high yielding varieties with more desirable traits.2.The relationship between genetic distance,heterosis and combining ability Present study was carried out to evaluate the relationship between parental genetic distances(GD),combining ability and heterosis in rapeseed.GDs among parental lines were measured from 11 morphological traits,and with SSR and SRAP molecular markers,respectively.Results revealed that GD evaluated by total molecular markers(GDtotal)had no correlation with heterosis and hybrid performance except setting position of the first primary branch.With the purpose of better prediction of heterosis,significant markers,favoring markers,and decreasing markers were selected from the total molecular markers,and results showed that GD measured by favoring markers heterozygosity(GDfavor)revealed highly significant correlation with heterosis and hybrid performance for all traits except seed yield.GD measured by decreasing markers heterozygosity(GDdecrease)showed significantly negative correlation with heterosis and hybrid performance for all traits.According to this research GDfavor(or GDdecrease)could be more effective for prediction of heterosis and hybrid performance for yield and yield components.Specific combining ability(SCA)may be another favorable parameter together with favoring markers or decrease markers for plant breeders in selecting elite hybrid combinations.3.Heterosis grouping of winter and spring rapeseed in Chinese rapeseed heterosis breedingIdentification of heterotic groups and heterotic patterns are of extreme importance to the success of rapeseed(B.napus)hybrid breeding program.In this investigation,five different heterotic grouping methods,which were based on SCA effects,SCA-Yang's effects,molecular markers,heterotic group's specific and general combining ability,and heterotic grouping based on the general combining ability of multiple traits,were compared for their ability to classify four testers and fourteen lines into heterotic groups.With regards to grouping of parental lines,breeding efficiency and cross mean yield variation explained by the cross types,the SCA-Yang's method was recognized as the best and most efficient method.On the basis of SCA-Yang's method,the four testers successfully classified 14 lines into four heterotic groups;the heterotic group 1 consisted Zhong7,Elect,9E49 and CZ25;group 2 consisted Zhong9,CZ05,9E38,CZ02 and CZ38;Group 3 comprised GZ1 R,SPArmada,Profit,9E54 and CZ49 and group 4 comprised SH11,Excell,CZ04,and 9E45.4.Analysis of genetic diversity among rapeseed cultivars and breeding lines by SRAP and SSR molecular markersThe knowledge of genetic diversity is very important for developing new rapeseed(B.napus)cultivars.The genetic diversity among 77 rapeseed accessions,including 22 varieties and 55 advanced breeding lines were analyzed by 47 SRAP and 56 SSR primers.A total of 270 SRAP and 194 SSR polymorphic fragments were detected with an average of 5.74 and 3.46 for SRAP and SSR primer,respectively.The cluster analysis grouped the 77 accessions into five major clusters.Cluster I contained spring and winter type varieties from Czech Republic and semi-winter varieties and their respective breeding lines from China.The 16 elite breeding lines discovered in Cluster II,III,IV,and V indicated higher genetic distance than accessions in Cluster I.The principal component analysis and structure analysis exhibited similar results to the cluster analysis.Analysis of molecular variance revealed that genetic diversity of the selected breeding lines evaluated was comparable to the rapeseed varieties,and variation among varieties and lines was significant.The diverse and unique group of 16 elite breeding lines detected in this study can be utilized in the future breeding program as a source for development of commercial varieties with more desirable characters.