| The experiment was carried out in Jin Jia town of Changtu County of Liaoning ProvinceTie Ling City, scientific research base of Shen Yang Agricultural University and keyLaboratory of Specialty Maize Genetics Breeding and Physiology of Shen Yang City from2009to2010. Using four large scale OPV varieties on production since1950s and thirty-onemaize hybrids and their parental inbred lines as experimental materials, evolutions ofagronomic traits, yield heterosis, dry material accumulation, physiological characteristics andqualities of Chinese maize varieties and their parental inbred lines during the yearreplacement were explored to define the importance of agronomic and quality traits to yieldformation. The main results were as follows:1. Yields of different year varieties increased with the advancing of era, and the averagegrowth rate among years were respectively16.7%,15.7%and21.6%under the low, mediumand high densities and the differences among years were significant or highly significant,which showed that effects of yield improvement were significant in recent years.Ear length,ear diameter, rows per ear and100-kernel weight of different year varieties increasedsignificantly with the increase of yield. Greater bald degree and lower seeding rate of recentyear varieties indicated that these two indexes developed in negative direction. Plant heightand ear height of1970S and2000S varieties were significantly higher than other years, andthe ratio of ear height/plant height of1970S varieties of were significantly higher than otheryears which indicated gravity centers of1970S varieties were higher, hovever, the gravitycenters of other years varieties were gradually reduced.During the year replacement, theangles of stem and leaf of all varieties gradually reduced while the LOV and value of greenduration obviously increased; branch number of tassel of recent year varieties significantlyreduced and rates of lodging and discount fell greatly. Correlation and path analysis showedthat100-kernel weight, rows per ear, grain number, ear length, ear diameter, grain length andLOV were highly significant positive correlation with yields under the low, medium and highdensity; the first three contribution rate on Yield were grain length, ear diameter and earlength.2. Yields of inbred lines increased with the increase of era, increasing margins of differentyear were from3.1%to37.3%under the three densities; ear length and grain number had notobvious change; ear diameter, grain length,100-grain weight and LOV showed increasing trends of different extent while lodging rate, discount rate, tassel length and branch number oftassel showed decreasing trends and the differences between recent year varieties and formeryear varieties were significant or highly significant, which indicated that the positiveimprovement of these traits was the main reason for yield increasing. Correlation and pathanalysis showed that100-kernel weight, ear diameter, grain length and LOV under the threedensity were significant positive correlation and ear width, ear length and LOV did morecontribution to yield.3.Yelds of different year single cross hybrids and their mid-parent values all took onincreasing trends with the advancing of era. Absolute heterosis increased with the advancingof era and average ratios of the absolute heterosis increased by3.9%,7.9%and18.8%respectively under the low, medium and high density, while the relative heterosis, mid-parentheterosis and heterosis indexes decreased slightly under the low and medium density but tooka slight upward trend under the high density; ultra-high-parent heterosis varied gentlybetween years and ultra-low-parent heterosis of1980S-1990S varieties was significantlylower than1970S. Through the analysis above showed that heterosis made more contributionsto yields under the low density, while heterosis got smaller and smaller with the increase ofdensities, which indicated that explaining factors made more contributions to yields.4. Dry matter accumulation of different year varieties increased wavely with theadvancing of era. Dry matter accumulation of1950S varieties were less than the other yearsvarieties in all stages; Dry matter accumulation of2000S varieties were higher than the otheryears varieties in late filling stage and dry matter accumulation of stem, leaf and sheath werehigher than the other years varieties in mature while the proportion of grain dry weight waslower and the economy coefficient was smaller. Comparisons of different year varieties, thestem translocation, transfer rate and grain contribution rate of1990S varieties were all thehighest; leaf translocation of1980S varieties were the highest while leaf transfer rate andgrain of1950S varieties were the highest; sheath translocation and transfer rate of1980Svarieties were the highest while grain contribution rate of1950S varieties were the highest.Filling intensities of1950S and1990S varieties were stronger but their duration were shorter;filling durations of1970S and1980S varieties were longer but their filling intensities weresmaller; varieties of2000S had stronger filling intensities and longer filling durations goodfor high yield. Dehydration rates from1950S to1980S varieties gradually accelerated whiledehydration rates of1990S and2000S varieties were significantly lower than other yearsvarieties. 5Determination results of net photosynthetic rate, chlorophyll content, protectiveenzymes and membrane lipid peroxidation content of ear leaves of different year varietiesshowed that with the advancing of era, the net photosynthetic rate increased; content ofchlorophyll a, chlorophyll b and chlorophyll increased and the trend were more obvious inlate filling stage; carotenoid/chlorophyll decreased, which indicated that green-stay of latervarieties were better that of early varieties, which would be helpful to later photosynthesis;activities of superoxide dismutase (SOD) increased and content of membrane lipidperoxidation (MDA) decreased, and the trend was particularly prominent in late filling stage,which indicated that the later varieties had stronger abilities of scavenging reactive oxygenspecies.6. Content of Starch from1970S to2000S varieties increased and average growth rateamong years were0.88%,0.81%and0.77%under the low, medium and high density, anddifferences between1970S and other year varieties were significant; content of fat, proteinand starch showed a negative correlation,which indicated that content of starch increasedwhile content of fat and protein decreasd during the variety replacement from1970S to2000S.Bulk density changed more gently and the differences among years were not obvious.Correlation analysis showed that content of starch and grain bulk density were positivelycorrelated with yield, while content of protein, fat and lysine were negatively correlated withyield. The analysis above showed that qualities gradually declined during the replacements ofmaize varieties in northern China.7. During the replacements of Inbred lines, content of starch and fat of1980S inbred lineswere higher than that of other years inbred lines while content of protein was significantlylower than other years inbred lines; content of lysine from1970S to1990S inbred linesgradually decreased. |
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