Establishment Of High-resolution SSR Primer System For The Classification Of Heterosis Groups In Maize

The classification of maize heterosis group is one of the most important concept and technology for modern maize variety improvement.The improvement of maize inbred lines is often crossed between similar groups,which not only produces new types of chromosomes number components of different parents,but also changes in special chromosome loci,including SSR molecular markers sites,due to exchange.These changes,especially the change of SSR locus,mean that the specificity of this site in the established SSR primer system decreases.Therefore,it is very important for the classification of newly maize inbred lines to screen new high polymorphism markers and establish a new SSR primer system,which is the routine work of maize molecular breeding.In order to establish new SSR primer systems,a total of 160 pairs of primers were selected,including the commonly used core SSR at present,and the SSR selected from SSR library,which were evenly distributed on 10 chromosomes,to detect the genetic diversity of 42 maize inbred lines whose heterosis groups were known.Then,the high resolution SSRs were used to screen for new primer system according to the PIC of each primer.And then,different SSR number primer systems were established selected from high PIC SSR with high resolution,high accurate classification and small detection workload.The established primer system was then tested in 104 inbred lines of known and unknown groups.The results showed that a set of new primer system composed of 40 pairs of primers and 20 pairs of primers was selected.The main results are as follows:1.A total of 160 pairs of primers were used to amplify on 42 materials with known groups.The results showed that 63 pairs of primers had stable band pattern and high polymorphism.The PIC values of the 63 pairs of primers were calculated by PowerMarkerV3.25,the highest being 0.7623 and the lowest 0.1545.According to the chromosome distribution of the primer and the PIC value of the primer on each chromosome,40 pairs,30 pairs,20 pairs and 10 pairs of four primer systems are respectively taken,by which the 42 materials were simulated classification.The results showed that the classification results of 40 and 30 pairs of primers were highly consistent with those of known groups,and the classification results of 20 pairs of primers were basically consistent with those of 40 pairs of primers,the classification results of 10 pairs of primer systems differ greatly from those of 40 pairs of primer systems.The results also showed that a total of 169 allelic variants were detected in 40 pairs of primers,and the number of alleles detected by each pair of primers was from 3 to 7,with an average of 4.225,and the gene diversity ranged from 0.498~0.80,with the average of 0.693,and polymorphism information ranged from 0.427~0.770,with an average of 0.631.A total of 101 allelic variants were detected by 20 pairs of primers.The number of alleles detected by each pair of primers was also from 4 to 7,with an average of 5.05.The gene diversity ranged from 0.638~0.803,with an average of 0.729.The polymorphism information ranged from 0.578~0.774.These parameters showed that the new 40 pairs of primers system and the 20 pairs of primers system with the lowest detection workload are as a group of new core primers system with high polymorphism and good classification effect.2.In order to verify the performance and resolution of the new primer system,40 pairs of primer systems and 20 pairs of primer systems were used to classify and verify in 104 maize inbred lines.The amplification results of 40 pairs of primers were analyzed by software Structure2.3.1.The results showed that when the number of groups(K value)was set from 1 to 15,the value of ? K reached the maximum at K=4,i e,104 inbreed lines were classified into four major germplasm groups,namely Reid,improved Reid,Lancaster and improved Huang,which were consistent with the results of the classification of dominant germplasm groups currently used in China.When the ? K value is set as 7,Lvda red cob and some unknown groups were identified,which were improved lines or mixed germplasm.In the same method,compared with 40 pairs of primers,the classification results of 20 primer system were completely consistent with those of 40 pairs of primers.A small number of mixed germplasm materials were classified in different sub-groups,but still belonged to the same heterosis group.These unknown groups are the improved lines or mixed germplasm between groups.These results as above suggested that 40 pairs of primers system had high resolution for the classification of maize inbred lines,and can identify known groups,unknown groups,intermediate types and other genetic resources,and can be applied to the accurate classification of heterosis groups of maize inbred lines.The classification by 20 pairs of primers system,small detection workload,are basically consistent with those of 40 pairs of primers system,which can be applied to primary classification for large quantities of maize inbred lines materials.