| The experiment was conducted at the Xinxiang experimental station of Chinese Academy of Agricultural Sciences in 2013~2014. The different genotypes of Maize Zhongdan 909(ZD) and Xundan 20(XD) were taken as material, and we set density and chemical regulation as treatment. The sowing density treatment was set to 4.5, 6.0 and 7.5, 9.0, 10.5 ×104 plants hm-2 five population densities, chemical regulation treatment was for six leaf stage application of Ethylene-Chlormequat-Potassium(ECK) 2 ml L-1 and control(CK) spraying water of the same volume. In morphology, lodging resistant mechanism and the level of enzyme, we have studied the development of two varieties of different densities, lodging resistance, leaf antioxidant, the leaf nitrogen metabolism key enzyme activity, and the effect of density gradient on the yield and yield constitute factors, then to explore the mechanism of the effect of density gradient on summer maize lodging and premature senility; on this basis, we have studied the effects of ECK on lodging-resistance and anti- premature senility of different density of summer maize. The results were as follows:(1) Sowing density higher than 7.5×104 plants hm-2 lead to the deterioration of the yield components, resulting in production decrease, ECK treatment optimized yield components, increase production. The relationship between yield and density of XD and ZD was conic. The highest Yield appeared in 7.5×104 plants hm-2; ECK treatment increased the yield of two varieties of different density populations; which, in high density populations(≥7.5×104 plants hm-2), XD-TR and ZD-TR yield have been increased than their respective CK significantly, increase range were 3.77%~8.15% and 6.73%~68.94% respectively. With the increase of sowing density, the number of ears per hectare increased, grain number per line and 1000 kernel weight showed the trend of decrease, and the line number per ear were not changed significantly. ECK treatment improves the effective ear number, 1000 grain weight, grain number per line of the two varieties significantly under high density populations(≥7.5×104 plants hm-2).(2) Increasing sowing density lead to stem slender, tall and soft, prone to lodging, ECK treatment lead to dwarf plant height, stalk thickening, and lodging resistance. The increase of sowing density significantly improved the plant height, ear height, gravity center height, length of basal internodes and lodging while decreased stem diameter, dry weight of unit length of internodes, breaking-resistance and lodging resistant index. Differences between varieties: lodging resistance of ZD is better than XD. ECK treatment significantly decreased the plant height, ear height and gravity center height, markedly shorten the length of internodes, increased the diameter, dry weight of unit length of internodes, breaking-resistance and lodging resistant index, and thus decreased the lodging, improved the ability of lodging resistance.(3) Increasing sowing density lead to dry weight per plant decreased, leaf area index(LAI) increased after anthesis; ECK treatment improve LAI and prevent premature of high density group. The individual dry matter weight decreased with the increase of density. LAI was increased with the density increase, but decreased gradually with the maize growth process and the LAI reduce amplitude was increased with the increase of sowing density; high density group easy to premature. ECK treatment increased the dry weight per plant and LAI of two varieties, and the effect of anti premature aging was significant.(4) Increasing density lead to the antioxidant properties of leaves decrease, leaves were easily premature, the oxidation resistance was improved by ECK treatment, and ECK prevented leaves from premature aging. With the increase of sowing density, ZD and XD individual leaf area showed a decreasing trend, and the decline range of each density in turn increases; the SPAD value and soluble protein content of different position leaves showed a downward trend; superoxide dismutase(SOD), catalase(CAT), and peroxidase(POD) activity was decreased; and the content of malondialdehyde(MDA) was increased; and there are differences between leaf position and variety about these indicators. ECK treatment significantly increased SOD, CAT, POD activity and SPAD value and soluble protein content, decreased MDA content of leaves at different positions of all population density, increase the leaf area per plant. The leaf area amplitude of high density populations decreased, and the leaf area of late filling stage was increased, and the leaf senescence was delayed.(5) Increasing density decreased the activity of key enzymes of nitrogen metabolism, lead to maize group premature easily; ECK treatment increased the nitrogen metabolism key enzyme activity, prevent premature senility. After anthesis, ZD and XD ear position leaf nitrate reductase(NR), glutamine synthetase(GS), glutamic oxalacetic transaminase(GPT), glutamic pyruvic transaminase activity(GPT) and free amino acid content were significantly decreased as the increasing of sowing density, ECK treatment significantly increased the activity of key enzymes of nitrogen metabolism of ear leaf and free amino acid content in the two varieties, promote the nitrogen metabolism, anti-aging effect is remarkable. |
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