Analysis On Gain Of Major Agronomic Traits For Maize Varieties And Parental Inbred Lines Form Different Decades In China

Maize(Zea mays L.)as an important cereal crop in the world and the production has been being increased dramatically since the introduction of heterosis. Analysising the yield gain of maize and agronomic traits will help understand the changes and problems in front of maize hybrids, so as to provide a theoretical reference for formulating breeding objectives and technology roadmap. In this study, being based on the methodology of quantitative genetics, we selected 34 varieties of maize form different decades for commercial production and 47 parental inbred lines to analysis comprehensively the evolution of yield and other agronomic traits under the pressure of different population densities and their contribution to the production. The main results are as follows:1. Comparing the data from Beijing and Hainan experiment sites, the result was that Beijing site was more serious diseases and insect pests, more adversity, more yield gain, the yield gain increased with the population density to increase faster; Hainan site was less diseases and insect pests, less adversity, smaller yield gain, the yield gain increased with the population density to increase slower. Just from the look of the yield gain, the ecological environment of the winter season in Sanya, Hainan Province is suitable for analysising the yield gain of maize varieties from different decates in China.2. The comparison of data from the two experiment sites, Beijingand and Hainan, revealed that less stresses the yield gain getting smaller, so increasing yields to a large extent depends on the improvement for stress tolerance or resistance. The results showed that the yield gap between medium and high population densities was smaller, and the maize improvement was mainly focused on the medium density, but improvement for high populationdensity was ignored completely.3. The development of agronomic performence showed increasing upright leaves began in the 1970s, ASI gradually narrowed, lodging rate decreased, ear length and ear diameter were slightly increasing, barren tip was longer, and grain weight were larger. The future of maize breeding should focus on the coordination of the relationship between 1000-kernel weight and kernels per row under the premise of increasing population density, continuously reduce the barren tip and lodging rate, maintain the high degree of heterosis, and improve the plant type. 4. The agronomic performance of inbred lines indicated that the improvement for yield and yield components of inbred lines was better, the average rate was 0.025 t/hm2/year; the higher the density, the greater yield gain; the yield of new inbred lines was higher than that of old ones during 1960s-1990s. The improvement for plant type of inbred lines was singnifecent. Leaf angle, plant height and ASI were decreasing; leaf orientation vaule, max leaf area and greenscore were increasing. Among ear traits, barren tip shortener, ear length, ear diameter and rows per ear remained basically unchanged, 1000-kernel weight and kernels per row were slightly increasing.