| Wheat is an important crop throughout the world,and also has an important position in China.There were several replacement of wheat cultivars in China,and studies have shown significant genetic improvement in wheat yield in the past decades.With the increasing population pressure and subsequent demand for agricultural products,promoting yield of winter wheat is still one of the goals in wheat production.Genetic improvement of wheat cultivar is an important way to promote yield.With year of released,traits of cultivars that did not meet practice need in production were eliminated,and excellent traits were retained and updated.Studying on the variation of yield and related traits of winter wheat cultivars released in different years,and exploring the physiological and morphological mechanism of genetic improvement of yield have practical significance to traits selection in breeding,and also provide theoretical guidance for breaking the limits of yield increasing.By using winter wheat cultivars which were widely promoted during 1940s to 2010s in Huang-Huai-Hai region,this study aims to systematic research the change of yield and yield components,dry matter accumulation and transportation characteristics,root distribution and water use characteristics,plant height composition,lodging resistance,photosynthetic ability and source-sink relationship during wheat cultivar replacement,and in order to provide theoretical reference and direction for future breeding work.(1)Winter wheat breeding has greatly increased yield by increasing grain number per spike and thousand grain weight,while spike number per m~2 did not change significantly.Harvest index has a significant increasing with year of released,but aboveground biomass did not show the same trend.The introduction of dwarf gene increased grain number at G3,G4position.Increasing of thousand grain weight and grain number per spike were occurred at four grain position,and varied between grain position from the 1940s to 2010s,while the relative contribution of grain weight to thousand grain weight at G4 has increased over time,it is much less than at G1,G2 and G3 and with the trend of G1>G2>G3>G4.(2)Dry matter accumulation and transportation characteristics and water use characteristics of winter wheat changed significantly with year of released.Post-anthesis assimilate accumulation,post-anthesis transportation of pre-anthesis assimilate,post-anthesis transport rate of pre-anthesis assimilate and contribution rate of pre-anthesis assimilate to grain yield increased significantly over time,but pre-anthesis assimilate accumulation did not show significant trend.The increase of post-anthesis assimilate accumulation had a significant effect on yield increase,and made the most contribution.Pre-anthesis assimilate accumulation,post-anthesis assimilate accumulation,post-anthesis transport rate of pre-anthesis assimilate and contribution rate of pre-anthesis assimilate had significant direct effect on yield increase.(3)Root dry weight in the 0-200cm and 0-20cm soil layers showed an increasing trend with year of released,and the same as root dry weight density of 0-100 cm soil layer.Drought in the late growth stage increased root dry weight in the 0-200cm,The increased part of root was in 20-200cm,which indicates that drought could promote root growth of modern cultivars deeper than old cultivars.Field crop consumption did not change with year of released.Water use efficiency increased significantly with year of released.(4)Wheat population structure and photosynthetic characteristics changed significantly with year of released.Modern cultivars have less non-productive tillers and higher leaf area index after anthesis than old cultivars.Plant height reduced significantly over time,the length of each internode decreased,and the decreased proportion were not the same of five internode.The proportion of peduncle in plant height increased significantly,while the proportion of 4th internode and 5th internode in plant height decreased significantly with year of released.Stem diameter,stem wall thickness and weight per unit length of 4th internode increased significantly over time,and stem strength had the same trend.The net photosynthetic rate and SPAD value of flag leaf at anthesis and mid-milky stage showed a significant increase with year of released,and positive related significantly to yield,grain number per spike and thousand grain weight.(5)Source-sink characteristics of winter wheat changed in Huang-Huai-Hai region since1940s.Leaves senescence was slower under defoliated treatment and faster under degrained treatment than control.SPAD value of top three leaves of old cultivars were more sensitive to defoliated and degrained treatment than modern cultivars,and compensation ability between the leaves showed the same trend.Absolute source showed a decreased trend over time.Defoliated treatment reduced dry weight of stem,leaves,sheath in mid-milky stage,promoted assimilate into sink,and degrained treatment increased dry weight of stem,leaves,and sheath.Modern cultivars were more sensitive to degrained treatment,while old cultivars were more sensitive to defoliated treatment.Absolute sink increased with decade of promoted.Post-anthesis assimilate accumulation decreased and post-anthesis transportation of pre-anthesis assimilate,post-anthesis transport rate of pre-anthesis assimilate and contribution rate to grain yield increased under defoliated treatment with decade of promoted.Degrained treatment reduced post-anthesis assimilate accumulation,post-anthesis transport rate of pre-anthesis assimilate and contribution rate of pre-anthesis assimilate to grain yield,and increased post-anthesis transportation of pre-anthesis assimilate over time.Compared with modern cultivars,old cultivars had relative big source and small sink,and with higher absolute source and compensation ability between the leaves.Modern cultivars have characteristics of relative small source and big sink.(6)Defoliated treatment reduced grain weight per spike and thousand grain weight,and the decrease were occurred at four grain position.G3 and G4 were more sensitive to defoliated treatment than G1 and G2,and declining degree of grain weight per spike and thousand grain weight under defoliated treatment increased with decade of promoted.Degrained treatment increased grain weight per spike and thousand grain weight,and G1 and G2 were more sensitive to defoliated treatment than G3 and G4,grains near the cob have priority to get assimilates.Final grain weight is influenced by both the competition of assimilate and sink size during grain filling.Limit of source of modern cultivars was stronger than that of old cultivars.Changes in source-sink related characteristics were concentrated on absolute source,relative source,and relative sink during the evolution of winter wheat cultivars in Huang-Huai-Hai region.There were both source limit and sink limit of winter wheat,and source-sink composite index increased significantly with year of released.Source-sink ratio decreased significantly over time,and the type of source-sink has changed from relative big source and small sink type to relative small source and big sink type. |
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