QTL Mapping And Genetic Dissection For The Uppermost Ear In Four RIL Populations Of Maize

Maize is a globally important food, economy and feed crop. How to improve maize yield per unit area is a major goal of maize breeding. Plant architecture breeding to improve the plant density and photosynthetic efficiency per unit area is a primary approach for achieving high yield in maize. An ideal plant architecture can be created to allow maize to fully capture and use solar energy at all growth stages and maximize maize yields per unit area. The internode length above the uppermost ear(ILAU) is an important influencing factor for canopy architecture in maize. Analyzing the genetic characteristics of internode length is critical for improving plant population structure and increasing photosynthetic efficiency. However, the genetic control of ILAU has not been determined. In this study, quantitative trait loci(QTLs) for internode length at five positions above the uppermost ear were identified using four sets of recombinant inbred line(RIL) populations in three environments,,constructing the SNP molecular marker genetic linkage map to mapping and analysis genetic effect for leaf traits through the method of composite interval mapping. Analysis the “consistency” ILAU traits QTL through the element analysis method, using four RILs population which constructed deriving from the Stiff Stalk plant type inbreed line Yu82 、Zong3 and Yu537 A and the non- Stiff Stalk plant type inbreed line Yu 87-1 and shen137. The major results are as follows:1. Three thousand and seventy-two SNP markers, derived from DNA-chip technology, were used to genotype the four sets of study populations consisted of 208, 197, 223, and 212 RILs derived from the crosses Yu82×Yu87-1, Yu82×Shen137, Yu87-1×Zong3 and Yu537A×Shen137, respectively. Using the software Jionmap4, with LOD score 2.5 and the largest genetic marker distance 20 c M, four genetic linkage maps were conducted, including 1179、1116、1243 and 1102 SNP markers, respectively. The lengths totaled 1873.02 c M、1839.75 c M、1863.00 c M and 1629.48 c M respectively and the average distances between markers were 1.59 c M、1.65 c M、1.50 c M and 1.48 c M in sequence. The four genetic maps integrate into a map which contained 2439 SNP markers, the total length of integration was 1933.74 c M and the average distance was 0.79 c M.2. Analyzing phenotypic performance of the internode length of five parents and four RIL populations, showed that all five trait values were markedly lower for Yu82, Zong3, and Yu537 A than for Yu87-1 and Shen137. For the RIL populations, the trait values exhibited high variability and transgressive segregation, with trait values exceeding the range of the parental lines. All traits were normally distributed in the four RIL populations.3. With the composite interval mapping method, QTLs detected for internode length above the uppermost ear in the four recombinant inbred line(RIL) populations across three environments. Seventy QTLs for ILFir, ILSec, ILThi, ILFor and ILFif were mapped to all maize chromosomes in the four RIL populations, with 16 QTLs in Pop. 1, 14 QTLs in Pop. 2, 25 QTLs in Pop. 3 and 15 QTLs in Pop. 4. The contributions to phenotypic variation for a single QTL ranged from 5.36% to 26.85%, with 27 QTLs > 10%. In addition, the following common QTLs were identified across two populations: one common QTL for the internode length of all five positions, one common QTL for the internode length of three positions, and one common QTL for the internode length of one position. In addition, four common QTLs for the internode length of four positions were identified in one population. The results indicated that the ILAU at different positions above the uppermost ear could be affected by one or several of the same QTLs. The traits may also be regulated by many different QTLs.4. Of the 70 initial QTLs, 46 were integrated in 14 meta-QTLs(m QTLs) by meta-analysis, and 17 of the 27 initial QTLs with R2 > 10% were integrated in seven m QTLs. Five of the key m QTLs(m QTL2-2, m QTL3-2, m QTL5-1, m QTL5-2, and m QTL9) in which the initial QTLs displayed R2 > 10% included four to eleven initial QTLs for an internode length of four to five positions from one or two populations. These results may provide useful information for marker-assisted selection to improve canopy architecture.