| Object: Maize grain yields have increased from about1900-2000kg ha-1in the1950s to5873kg ha-1in2012in China. Maize varieties have been upgraded5-6times, and planting density and fertilizerapplication increased, planting patterns improved with yield increase. Previous studies had focused onyield traits, physiological characteristics, resistance to stress, etc, from the viewpoint of improving maizevarieties, which were systematic works. This study is to research maize morphological characteristics,population structure and function, define changes of those above during yield improvement, with the keypoint of yield improvement; and also compare yield changes in the three areas, analyze how ecologicalconditions to effect on maize yield gain during yield increase. These results will provide theoretical basisand technical support for breeding and selecting maize varieties, improving agricultural measures.Method: This study included11maize varieties released from the1950s to2010s (1950s OPCs: Baihe,Yinglizi;1960s: Jidan101;1970s: Zhongdan2;1980s: Sidan8, Danyu13, Jidan180;1990s: Yedan13;2000s:Zhengdan958and Xianyu335;2010s: Nonghua101) that have been widely used in China. These varietieswere planted at a range of plant population densities (37500,52500,67500, and82500plant ha-1) andnitrogen applications (0,150,225, and300kg N ha-1), which were performed at the CAAS NortheastResearch Station (Gongzhuling, Jilin Province) between2011and2012. The experiments were arranged ina split-split plot design with nitrogen treatments as the main plots, planting densities as subplots, and maizevarieties as the sub-subplots, which to simulate scenario of maize production over the past60years. Thestudy is to analyze the change rules of those indexes during yield improvement by investigating plantmorphological traits (plant height, ear height, internode length, internode diameter, leaf angle, leaf area perplant), population structure (LAI, VDLA), population quality (lodging, empty plant, light distribution) anddry matter accumulation at different periods (stem, leaf, grain), yield traits (yield per unit area, yield perplant, ear number, grain number per ear and grain weight) and so on. The study is to also analyze thedifferences on biomass, yield per unit area, yield per plant and ear characters between locations throughtesting those at Changji in Xinjiang province, Gongzhuling in Jinlin province, and Xinxiang in Henanprovince in2011and2012.Results:The following results were obtained by the experiments in2011-2012:(1) Changing trends of biomass and yield on maize varieties released in different eras. The biomass ofpopulation was increased after flowering, and the harvest index or yield had improved with upgradedmaize varieties. With plant density increase, grain yield per plant of all maize varieties were decreased. Theolder maize varieties had high yield under low plant density while the new varieties yielded high underhigher plant density. The grain yield per plant and yield per unit area had improved with the application ofnitrogen fertilizer increase. In addition, the yield components had all increased with the improvement ofmaize varieties. Plant density increase made ear number increased while made grain number per ear andhundred grains weight reduced. Those components were all increased with the application of nitrogen increase.(2) Changes of plant morphological characteristics and population structure during the maize yieldimprovement. Plant height was increased slightly and ear height was decreased by20-38cm, the lengths of2-4internodes and the mean internodes length below ear were all significantly decreased, numbers ofleaves of all maize varieties were stable which kept between22and23, with the maize varieties upgraded.Leaf area of per plant was increased from the1950s to the1990s, and decreased slightly after the1990s.Leaf angle of the whole plant became smaller (decreased from42°to30°), LOV was increased (increasedfrom33°to51°), especially above the ear. Leaf area index of population increased with maize varietiesimproved because of the optimum of plant density for high yield. There was increase in plant and earheight, ear coefficient, decrease in leaf angle and leaf area per plant, improvement in LAI when plantpopulation was increasing. With nitrogen application increase, plant height and ear height were bothincreased, leaf angle was increased, LOV became smaller, and leaf area per plant was increased.(3) Population quality had been optimized during yield improvement. With the improvement of varieties,the transmittance of each depth in the canopy increased. Even at the high plant density, light distribution inthe bottom of canopy for modern hybrids was keep at0.04-0.05. Stem lodging decreased significantly withupgraded genotypes. Modern hybrids have stronger resist to lodging than old ones. Average empty plantrates obviously reduced at a rate of0.16%-0.29%/year when new hybrids replaced old ones. With thedensity increasing, stem lodging and empty plant ratio increased, while the light transmittance of thecanopy reduced. Nitrogen fertilizer increase made stem lodging increased but empty plant rate decreased.From relations between morphological characteristics and population quality, it showed the direction ofleaves and light distribution in the canopy were significantly correlated; correlations between ear height,numbers and length of internodes below the ear and stem lodging were significantly positive.(4) Yield gains in the different regions. Ecological conditions markedly influence the maize developmentand matter accumulation, which both affect maize yield. The results of experiments that were conducted inthree different regions (Changji, Gongzhuling, Xinxiang), showed the days of growth period and fillingstages had prolonged with maize varieties improved. It was the order of Changji> Gongzhuling> Xinxiangwhen compared to growth period in three areas. The average matter accumulation and yield were the orderof Changji> Gongzhuling>Xinxiang even at the optimum cultivation. From the1950s to2010s, yieldgains of Changji, Gongzhuling and Xinxiang were respectively8.81,7.14and7.98t/hm2. The contributionof genotype to yield increase was highest in Xinxiang about62.74%. Agronomic management contributed34.74%to yield increases in Changji, more than its contribution in Gongzhuling or Xinxiang. Thecontribution of genotype and agronomic management interactions to yield gain in Gongzhuling was29.89%. Further analysis of yield gain based on the basic yield in the1950s revealed relative yield gainratios of1.33,1.13, and1.92times in Changji, Gongzhuling, Xinxiang, respectively, resulting fromimprovement in genotypes and cultivation since the1950s. In Xinxiang, relative yield gain ratios was1.21times due to new hybrid breeds. Conclusion: During maize yield improvement, the days of growth period increased and number of leavesper plant neither increased nor decreased. Plant height increased and ear height decreased with upgradedvarieties. Leaf area per plant and LOV had increased, leaf became more upright over time. Lodging andempty plant decreased while light transmittance of the layers in fully canopies increased with improvinggenotypes. Lengths of internodes elongated and stem lodging increased when plant density and nitrogenapplication increased. Leaf area per plant decreased and LAI increased, light transmittance below the eardecreased, with increasing plant population. New hybrids have reasonable light distribution in the canopiesat the higher densities resulting from having more upright leaves. The decrease in stem lodging of newhybrids was due to numbers and lengths of internodes below the ear reduced with increasing year ofrelease. So these results demonstrated that the changes of morphological characteristics of maize varietiesreleased in1950-2010optimized population structure, and improved grain yield. It showed maize yieldsand the contribution to yield gain were different among regions even at the same genotypes and cultivationby different ecological regions experiments. In this study, the order of grain yield was Changji>Gongzhuling> Xinxiang while the order of genetic contribution to yield gain was Xinxiang> Changji>Gongzhuling. Our results imply that the genetic contribution to yield gain was obviously high in poorecological conditions. To continue increasing maize yield in China, breeding for improved adaptation todifferent environments is required. |
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