Studies On Heterotic Grouping And Combining Ability Of Yield Properties Of Current Main Maize Germplasm In Sichuan Province

Maize?Zea mays L.?is a member of the grass family?Poaceae?and a member of the genus Zea.As one of the main food crops,feeds and industrial raw materials,maize is widely distributed in various countries around the world;increasing yield and improving quality have always been the main targets for maize breeding.Here,Hundreds of current maize inbred lines from several major maize breeding units in Sichuan province were collected in this study.First,gentotyping by sequencing?GBS?was used to determine the genetic relationship among these inbred lines.Meanwhile,the combining ability effects of 17 yield related traits of inbred lines were analyzed according to the NC II genetic mating design to evaluate the utilization potential of each inbred line.Then,the candidate SNP markers or genes for the general combining ability?GCA?of 17 yield related traits such as ear length?EL?,ear diameter?ED?,kernel row number per ear?KRN?and kernel number per row?KNR?were detected by genome-wide association study?GWAS?strategy.The main results of this study are as follows:?1?4,976 SNP markers were developed by GBS in 157 current maize breeding lines in Sichuan province.The allelic variation of SNP molecular markers was 3 to 5,with an average of 3.22;the gene diversity?GD?was 0.1470⁰.7512,with an average of 0.5066;and the polymorphism information content?PIC?was 0.1371⁰.7107,with an average of 0.4132.The population structure analysis based on the SNPs indicated that 157 inbred lines could be divided into I,II,III,IV 4 subgroups:8 maize germplasms such as Mian765 were clustered into I group,63 maize germplasms such as 18-599,Mo17,Qi319 and Ye478 were clustered into II group,57 Maize germplasms such as 08-641,Dan 340,B73 and Huangzao 4 were clustered into III group,20 maize germplasms such as SCML104 were clustered into IV group,and other 9 maize germplasms were clustered into mixed subgroup for the genetic similarity ratio of these inbred lines is low to any other subgroups.According to the pedigree of lines in each subgroup and the ecological attribute of Sichuan,the I,II,III,IV subgroups were named Impro-local,Tem-tropic I A,Tem-tropic I B and Impro-tropic Subgroups,respectively.Genetic diversity analysis showed that the Tem-tropic I B germplasm had the most abundant genetic diversity and the Tem-tropic I A germplasm had lower genetic diversity.The population genetic relationship between Impro-local and Impro-tropic is far,and the population genetic relationship between Temp-tropic I A and Tem-tropic I B is the closest.The average LD decay distance of 157 maize inbred lines was 1.05¹.10Mb.The results of this study verified that tropical and subtropical germplasm was introduced into Sichuan during the maize breeding process,forming a large number of Tem-tropic germplasm here.?2?The results of GCA effect analysis for 17 yield related traits of current maize breeding lines in Sichuan province showed that LH8012,T237,T278 and T318 have better ELGCA effect;Yi13B1-3 and78599-211 have better BTLGCA effect;Y1018,Y1126,Y1114 and Mian1708 have better EDGCA effect;Mian723,T309,C328,Mian0232,Y1126,Y1018 and Mian1708 have better KRNGCA effect;08-641 and SCML7275 have better KNRGCA effect;Mian1834,T145,Mian757 and CZ2142 have better CDGCA effect;Mian0232 and Yi098 have better KLGCA effect;Y1114,heat anti-67,N29,T260and Yi14A13 have better KWGCA effect;91?2?6983-0 has better KPRGCA effect;Nan942 and GermanyX-02 have better KMGCA effect;Y1114 and Y1018 have better EWGCA effect;Y1018 and Y1114 have better KWPEGCA effect;Chengyu No.10 male parent,Yi14A2,Nan942 and T96 have better CWGCA effect;Y1114 and heat anti-67 have better HKWGCA effect;T318,Suwan1611,Mian722,Y1126,Y1018,78599-211 and Mian1708 have better KTWGCA effect;91?2?6983-0,Y1018and Y1114 have better GYPPGCA effect;91?2?6983-0 and Y1018 have better GYGCA effect.Based on the evaluation of 17 GCA traits,the top ten inbred lines with good performance and balanced GCA effects in both two environments were Y0921,91?2?6983-0,T213,T42 L648,T71,Y1018,Mian722,SCML30331,13B1-3 and 15B5.?3?In the 635 cross combinations,the top three hybrids at JH with high GYPPSCA were ShuangM9×LH8012,SCML7275×08W_SC149-221,Y1018×Y1027;and Yi ZB-8×Y1027,Jingke968female parent×Mian04185/SN8,T145×PH6WC at YA.According to the SCA effect of grain yield per plant,144 maize inbred lines were divided into 4 groups at both JH and YA,but the specific lines in each cluster are not exactly the same in the two different environments.?4?The GLM model in TASSEL software was used for GWAS based on the population structure and genetic relationship with 4,976 high-quality SNPs.At the significance level of-Log₁₀P>3.70?P<1/4,976?,239 SNP loci associated with the general combining ability of yield related traits,which distributed on 1 to 10 chromosomes of maize,and could explain 10.90%²9.21%of phenotypic variation by a single SNP,were detected in two environments.Among these SNPs,5 sites were associated with ELGCA,1 sites were associated with BTLGCA,29 sites were associated with EDGCA,1 sites were associated with KRNGCA,3 sites were associated with KNRGCA,7 sites were associated with CDGCA,1 sites were associated with KLGCA,1 sites were associated with KWGCA,8 sites were associated with KPRGCA,18 sites were associated with KMGCA,28 sites were associated with EWGCA,28 sites were associated with KWPEGCA,19 sites were associated with CWGCA,5 sites were associated with HKWGCA,9 sites were associated with KTWGCA,38 sites were associated with GYPPGCA,and 38 sites were associated with GYGCA.At the significance level of-Log₁₀P>3.00?P<0.001?,25 sites associated with GCA of 12 yield related traits such as EDGCA,KRNGCA and KNRGCA were detected in both two environments.The development of these SNPs associated with GCA of yield related traits will facilitate the application of GWAS in maize,and provide a reference for molecular marker-assisted selection?MAS?breeding of maize in the future.