Quantitative Genetic Research Of Main Agronomic Traits Under Different Planting Density Treatments In Maize

Maize is one of the most important food, feed and economic crops in the world. Maize yield has a great impact on world food security. In recent years, increasing plant density and selecting the densitytolerance varieties have been the effective strategies for breeding stable and high yielding maize. Studying the genetic mechanisms on the agronomic traits under different planting densities can provide theoretical bases for density-tolerance maize breeding. To elucidate the impact of plant density on the genetic basis of maize agronomic traits, a recombination inbred line(RIL) mapping population was developed from the cross of two maize inbred lines, Zheng58 and HD568. The genetic linkage map was constructed with SNPs evenly distributed on maize genome. Maize agronomic traits, including the plant height, ear height, stalk diameter, leaf area, the number of tassel primary branches and so on, were collected in three environments under three planting densities for detecting density stable and sensitive QTL. The main results were summarized as follows:1. Planting density had a significant effect on main agronomic traits. Phenotype of all agronomic traits between two parents were greatly different, and the RIL population exhibited mid-parent heterosis. Analysis of joint variance indicated that environments, families, densities and the interaction among different factors had significant influence on maize agronomic traits. The heritability(H2) of these traits were relative high and had a little difference under three planting densities.2. Using the inclusive composite interval mapping method, QTL for main agronomic traits were detected with phenotypic values in different environments and BLUP values. The results showed that 22 non density-specific QTL marker intervals and 4 density-specific QTL marker intervals and 98 stable QTL in total, which related to stalk traits were repeatedly detected under multiple densities and environments. Three major effect QTL related to plant height were found in the marker interval SNP2105-SNP2109 and SNP2095-SNP2111 in chromosome 7 and marker interval SNP1469-SNP1476 in chromosome 5. Two major effect QTL related ear height were detected in the marker interval SNP0045-SNP0047 and SNP0255-SNP0259 in chromosome 1. One QTL among them located in SNP0045-SNP0047 have been reported by previous studies. Three major effect QTL marker intervals were found in the stalk diameter and they located in marker intervals SNP0097-SNP0099, SNP2612-SNP2616 and SNP0097-SNP0099 corresponding to the chromosome 1, 8, 9 respectively.3. The genetic model of leaf area above the uppermost ear fitted the addictive interaction between two inhibited major genes and polygene that were control by major gene and minor polygene, which to be affected by the environment. 18 non density-specific, 10 density-specific QTL marker intervals and 113 stable QTL in total were repeatedly detected under multiple densities and environments in leaf traits above uppermost ear. One density-specific major QTL and one non density-specific QTL were found in chromosome 1 and 6 in leaf length above uppermost ear. Two non density-specific major QTL were found in the chromosome 6 and 9 in leaf width above uppermost ear. And three non density-specific major QTL were found in the chromosome 1, 2 and 7 in the leaf angle above uppermost ear.4. Eleven non density-specific, 4 density-specific QTL marker intervals and 57 stable QTL in total were detected in tassel relative traits. One non density-specific major QTL was found in the marker interval SNP0969-SNP0975 of chromosome 4 in the length from the highest branch to the top of tassel spindle. One density-specific and one non density-specific major QTL were found in the marker interval SNP0648-SNP0655 of chromosome 2 and SNP1938-SNP1939 of the chromosome 6 respectively.