| Wheat is an important cereal crop in the world.Henan Province is one of the main wheat producing areas in China,where the genetic improvement of wheat cultivars has made the constant increase of wheat yield during the recent 70 years.The present study was aimed at studying the genetic improvements in yield,yield components and associated biological characteristics of wheat cultivars grown in Henan Province by using 30 cultivars released in various periods from landraces to new cultivars planted in 21st century.The results showed that the yield level of wheat cultivar had been increased remarkably due to cultivars substitution in Henan Province.There were more than two times(108.8%)of increase of yield for new cultivars in comparison with the landraces based on the current culture techniques,and the annual genetic gain was 1.81%.The main changes of yield components were increases of thousand grain weight and grain number of spike during the wheat genetic improvement process over the past 70 years in Henan Province,and especially the thousand grain weight contributes the most to the increases of grain yield.The number of spikes in unit area was almost unchanged.The aboveground biomass and harvest index all had increased in genetic improvement of wheat in Henan Province,and the most remarkable genetic improvement was harvest index,that the annual genetic gain was 1.38%.The bases of biology for grain yield genetic improvement in Henan Province were analyzed on the genetic improvements in the accumulation,distribution and transportation of assimilates in various periods,and source-sink relationship.The results showed that assimilate increasing after anthesis was an important base of yield genetic improvement.Compared with the landraces,the accumulation of assimilate of modem cultivars was increased by 53.5%,and the annual genetic gain was 1.78%.The factors of the assimilate increasing after anthesis were the constant increase of the photosynthesis rate and leaf area index.The photosynthesis rate of flag leaf had significantly increased at anthesis and 25 days after anthesis,respectively,over the past 70 years in Henan Province,and the annual genetic gains were 0.58%and 0.29%,respectively.At the same time,the leaf area index of modern cultivars also had an significantly improvement compare with the landraces.With yield rising,the output rate of assimilate accumulated before anthesis was increased from 8.91%for landraces to 31.99%for modem cultivars.The results of assimilates distributed to each vegetative organ showed that the assimilate accumulation of sheath and stalk of modern cultivars didn't decrease compare with the landraces at anthesis,but decreased significantly at mature period,and the panicle weight increased significantly.The analysis of source-sink relationship suggested that the absolute source and the absolute sink were smaller,and source was relatively larger than sink for old cultivars.The absolute source and the absolute sink were larger,but source was relatively smaller than sink for modern cultivars.The results indicated that the restriction factor was accumulation of assimilate for increasing yield in future.With respect to the plant architecture,the most remarkable genetic improvement was the decreased of plant height.Plant height decreased from 133.53cm for landraces to 76.86cm for modem cultivars,and the annual genetic gain was 0.71%.In addition,the gravity center of leaf layer had significantly decreased,leaf area increased continuously,and the space structure of leaf layer transformed from hanging type to erect type.The findings in the current study indicate that during the process of wheat genetic improvement in Henan Province,not only has dwarf breeding made great achievements,but breaking strength breeding has also achieved a remarkable result comparable to the former.The breaking strength of stems has significantly increased from 2.10 and 1.27 N/single-stalk to 4.59 and 2.63 N/single-stalk at anthesis and 25 days after anthesis,respectively,over the past 70 years in Henan Province,and the annual genetic gains were 1.99%and 1.78%,respectively.In the process of wheat genetic improvement,the morphological structure and chemical components of stalk relate to lodging resistance also had significantly improvement.Compared with previous wheat cultivars,the stems of modern ones are bigger,the stem wall is thicker,and the lignin content is higher,which was the main reason of breaking strength increased continuously.Finally,a discussion was made on the genetic improvement of wheat yield in future. |
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