Study On Development Law Of Yield And Agronomic Characteristics Of Maize Varieties And Iibred Lines In Different Eras

As one of the earliest heterosis utilization crops in the world, maize takes the second place in both total production and yield, is extremely important to grain production in China. Application of the new maize varieties is the core of yield increase. One of the hotspots in maize genetics and breeding is the evolution of maize varieties and parent inbred lines yield and its agronomic characteristics. The split-plot design of two factors which main plot are densities and assistant plot are maize varieties and inbred lines was adopted in this experiment. By the methods of analysis of variance, mutiple comparison, correlation analysis and path coefficient analysis, the evolution of yield and agronomic characteristics of maize varieties from 1950s to 2000s and inbred lines from 1970s to 2000s, as well as the relationship between heterosis and yield were stduied in Xinjiang. The main results as followed.1. The yield of maize progressively increased from 1950s to 2000s. Evolution of maize varieties yield could be divided into three stages:significantly increasing stage from 1950s to 1970s, slightly increasing stage from 1970s to 1990s, highly increasing stage from 1990s to 2000s.2. The yield genetic gains of maize varieties were 0.0732,0.1122 and 0.1125 ton.ha-1.year-1 at the density of 15000,45000 and 75000 plants.ha-1 respectively, and the average yield genetic gain was 0.0993 tan.ha-1.yeaf-1. The density-tolerance of maize varieties was not improved.3. The 1000-kernel weight, kernels per ear, kernels per row, ear length, ear diameter and bald head length of maize varieties showed increasing trend from 1950s to 2000s, but the grain index, ASI, disease plant ratio and stem and root lodging ratio showed decreasing trend. The evolution of plant height, ear height and growth duration had no regular pattern.4. The increase of kernels per row was a crucial factor raising yield of maize varieties. The increase of ear diameter, ear length,1000-kernel weight, plant height and growth duration also played important roles to yield. The decrease of grain index limited the yield increase from 1950s to 2000s. Therefore, maize variety breeding must emphasized on selection of kernels per row,1000-kernel weight and ear length, properly increasing the plant height and growth duration, coordinating the relationship with the grain index.5. The yield of parent lines of maize hybrid was well improved from 1950s to 2000s. The yield genetic gains of inbred lines were 0.0105,0.0268 and 0.0348 ton.ha-1.year-1 at the density of 15000,45000 and 75000 plants.ha-1 respectively, and the average yield genetic gain was 0.0240 ton.ha-1.year-1. The density-tolerance of inbred lines was not improved.6. The 1000-kernel weight, kernels per ear, ear length and ear diameter of inbred lines represented increasing trend from 1970s to 2000s, but the disease plant radio, stem and root lodging radio, bald head length and ASI showed decreasing trend. The evolution of kernels per row, grain index, plant height, ear height and growth duration had no regular pattern.7. The most important reason of inbred lines yield increase was the decrease of ASI. The kernels per row and ear diameter also played important roles for yield increase. Moreover, maintaining certain plant height and grain index was a major factor for achieving high yield of inbred lines.8. The contribution rate of heterosis to yield declined with density increasing. In additional, the contribution of heterosis to yield was decreasing, and the trend more obvious in height density.