The Use Of Marker-Assisted Backcrossing For Waxy Maize Lines Breeding

Waxy maize lines and high performance combinations were rapidly developed through marker-assisted backcrossing using the normal maize inbred line 851213 as accepter parent and waxy maize line zhongyu 08 as donor parent. Application of marker-assisted backcrossing (MAB) in waxy maize lines improvement will provide useful experience in maize marker-assisted selection breeding programs.The main results were as following:1. The average proportion of recurrent parent genome (PRPG) was 74.26% analyzed by 80 SSR markers in 182 BC1F1 plants detected by pollen microscope examination as heterozygous genotype and the highest was up to 88.67%. 16 individuals accessed to next backcrossing generation through the selection criteria of PRPG above 80%. The average PRPG was 89.66% analyzed by 105 SSR markers in 16 BC2F1 families derived from the 16 BC1F1 individuals detected by pollen microscope examination as heterozygous genotype. The highest PRPG was up to 94.86% and the lowest was 83.2%. The highest PRPG derived from 2 continuously backcrossing generations and selected by MAB in this study was slightly lower than 96.9%, the theoretical average PRPG of continuously backcrossing for 4 generations (BC4F1). The result showed that MAB can speed up 1～2 generations than classical backcrossing programs.2. There are significantly positive correlations (p<0.01) of PRPG estimated by different SSR markers in terms of number in BC1F1 and BC2F1 population. The Pearson correlation coefficient was 0.95 of PRPG estimated between 50 and 80 SSR markers in BC1F1 population and 0.96 of PRPG estimated between 90 and 105 SSR markers in BC2F1 population showed similar results respectively.3. The PRPG of BC1F1 plants was negatively correlated with the yield characters of BC2F1 families: grain weight per ear, rows per line×kernels per row×100-seed weight, kernels per row, ear length and 100-seed weight. The Pearson correlation coefficient was -0.315, -0.294, -0.288, -0.244 and -0.19 reached 0.01 level significance. The results show that the correlation coefficient was too low to infer the relative level of PRPG from the degree of inbreeding depression.4. All the test crosses hybridized between the selected BC2F2 lines of 851213 and waxy lines of Mei 22 were identigfied by the yield profermance experiments. The result showed NW85-01, NW85-04, NW85-09, NW85-10, NW85-11 and NW85-15 were the best lines with higher general combining ability, simultaneously; the top ten combinations were selected for advanced variety trials based on the average relative productivity of waxy maize lines of 851213, hybrids yield and its relative productivity. These combinations are as following: NW1786x NW85-11, NW1736x NW85-09, NW1721x NW85-05, NW1726x NW85-15, NW1731x NW85-15, NW1716x NW85-08, NW1711x NW85-10, NW1761x NW85-15, NW1736x NW85-12, NW1751×NW85-04.5. The Pearson correlation coefficient between average relative productivity of waxy version of 851213 and the PRPG of BC1F1 and BC2F1 plants was -0.128 and 0.151 did not reached significance. Therefore, it's difficulty to predict the yield performance of hybridized combinations through its PRPG of BC1F1 and BC2F1 populations. So, the GCA of improved waxy lines would identified by the performance of its testcrosses.