| Southern leaf blight(SLB) is an important disease in maize, and the cause of the disease still increases year by year, in this trend of increasing SLB damage was greatly attented by corn plant breeders. To develop SLB resistance sweet corn varieties is an important means to save diseases of maize yield and output value caused by SLB. This mean has many characteristics, such as economic, safe, direct and effective. SLB resistance and main agronomic traits QTLs detected in this study, the major results were as follows:1. Traditional plant disease resistance identification standard is based on the degrees of disease levels.This method is a visual subjective evaluation, and the data is discontinuous. With this kind of strong subjective evaluation method, the discrete data can’t satisfy the requirements of quantitative trait locus mapping. The shortcomings of traditional evaluation on SLB resistance was overcome in study by different statistical method, such as image background segmentation, health and disease leaf recognition and pixel transformation, with using Photoshop image analysis software.This method in study could be used to get measurement data of SLB resistance accurately, and the data had the characteristics of continuity, accuracy and objectivity.This study method could get the total plant southern leaf blight area and the total plant leaf area. The ratio of the former and the latter was named Leaf blight coefficient(LBC). The experiment of 200 strains of sweet corn in F2 population has carried on the statistical analysis of SLB resistance. F2 plants LBC range between 2.004% and 53.706%, kurtosis of 1.656, 1.165 of skewness, coefficient of variation of 53.67%; Whole plant southern leaf blight area range between 42.573 cm2 and 1827.723 cm2, kurtosis of 3.010, 1.469 of skewness, coefficient of variation of 58.10%.2. Tow sweet corn inbred lines T8( SLB-fected) and T33(SLB-resistant) were obtained from Crop research of Zhongkai University of agriculture and engineering. F2 generation population were built using these inbred lines T8(♀) and T33(♂) in 2014, with continuous 200 strains F2 generation planted as the experimental material. With studying a lot of relevant papers published abroad and inland, 600 pairs of SSR primers were selected, and 253 pairs of polymorphic SSR primers were selected from 600 pairs of SSR primers by polymorphism screening, only 214 pairs of SSR primers were used to construct linkage map. Linkage maps were constructed using 214 SSR markers covering a total map length of 1270.167 c M. The average distance between mapped markers was 5.935 c M. The distance between mapped markers range from 4.470 c M to 9.316 c M, meeting the requirements of the QTL mapping.3. For SLB resistant QTLs mapping on sweet corn, 4 QTLs releted plant LBC in this experiment were detected in phi453121- umc1746(3.00 3.01) bin, umc1746- bnlg1523(3.01 3.02) bin, bnlg603- mmc0081 bin(5.05) and bnlg2097- umc1133 bin(6.03), contribution rate were 11.17%, 11.32%, 9.05% and 11.32% respectively. For whole plant leaf blight area in this experiment, 7 QTLs were detected in umc1746- bnlg1523(3.01 3.02) bin, umc2049- phi099(3.02 3.04) bin, umc1926- umc1759(4.02 4.03) bin, nc005-umc1088 bin(4.05), umc1491- umc1587(5.00 5.03) bin, bnlg603- mmc0081 bin(5.05) and bnlg609- bnlg1306 bin(5.07), contribution rate were 9.49%, 8.95%, 4.86%, 5.98%, 15.93%, 10.90% and 9.16%. The spacing of q PSLBA-chr4-2 and nc005 loci was very small, spacing of q PSLBA-chr5-3 and bnlg1306 was also small.4. For QTL localization on SLB resistance and main agronomic traits of sweet maize, 59 QTLs were detected. Number of plant related QTLs was 20, number of related QTLs was 26, number of SLB disease resistance related QTLs total 13. 2 QTLs releted plant leaf area were detected in 7, 9 chromosome with contribution rate of 15.06% and 20.34% respectively. 6 QTLs releted fresh ear brix detected in 1, 3, 8 on chromosome, with phenotypic variation range of 6.71% to 14.83%. Plant type traits QTLs mainly distributed in 3, 4, 6, 7, 9 chromosome; ear traits QTLs mainly distributed in 3, 6, 7 chromosome; disease resistance trait QTLs are in 3, 4, 5, and 6 chromosome. Most detected QTLs in chromosome 3, totaled 17 QTLs. The following were chromosome 6, 8 QTLs. The next were the 4 and 7 chromosome, both totaled 7 QTLs. In chromosome 3, phi453121-umc2049 and umc1908-umc2275 was QTLs concentration areas. Umc1753- bnlg2191 in chromosome 6 and bnlg339-umc1154 in chromosome 7 were QTLs concentration areas, too. Therefore, it should be centered on these areas in QTL mapping. This study was expected to be the theoretical basis for SLB resistance breeding of sweet corn marker-assisted selection. |
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