| Keeping improvement the yield per unit area is the hard requirement of wheat production in China.Increasing planting density is one of the important measures to increase yield per unit area.With the increase of planting density,the stem is slender,the degree of fullness is reduced,and the amount of lignin accumulation is reduced,the wheat population quality becomes worse.It is easy to have a large area of lodging.Different lodging resistant cultivars have different performance in stem morphological index due to the difference of genetic background.Therefore,to study the difference of lodging resistance in different lodging resistant varieties of wheat is helpful to breed and increase the lodging resistance of stem.The stalk of wheat has both mechanical stiffness and flexibility.Therefore,the evaluation of stalk quality of wheat should be considered comprehensively.The research proves that reasonable nitrogen fertilizer timing can improve the lodging resistance of wheat stalk and the quality of wheat stalk can be improved by applying basal fertilizer: fertilizer: jointing booting fertilizer1:1:1.On the premise of appropriately increasing the density,lodging resistant variety jimai(JM22)and lodging sensitive variety shannong 16(SN16)were selected in this experiment.The density was 3 million plants per hectare,nitrogen fertilizer was applied with 300 kg per hectare,1/3 of nitrogen fertilizer and all phosphate fertilizer and potash fertilizer were applied as basal fertilizer,and the remaining 2/3 of nitrogen fertilizer was applied with four topapplication modes.in the elongation stage,full fertilizer(CK);In the standing to jointing stage and booting stage,1:1 fertilizer(T1);in the elongation stage and anthesis stage1:1fertilizer;(T2)in the booting stage,full fertilizer(T3).The differences of lodging resistance of different lodging resistant varieties under the same treatment and the effects of nitrogen fertilizer timing on the lodging resistance of whole wheat stem were expounded from the aspects of the internode apparent characteristics,mechanical characteristics and lignin metabolism of stem.In order to improve stem quality to provide theoretical basis and support for optimizing cultivation measures.The main results of this experiment are as follows:1.Effects of nitrogen fertilizer timing on stem apparent traits of wheatDifferent fertilizer timing had a certain influence on stem lodging resistance of wheat.In the experiment,anthesis stage,filling stage and maturity stages were selected to measure the apparent traits of wheat plants,including plant height,node length,center of gravity height,stem thickness,wall thickness and stem fullness.The results showed that there was no significant difference in plant height among different cultivars,the sensitive cultivars with high barycentric height lodging were higher than those lodging resistant varieties,and the proportion of barycentric height in plant height increased significantly with the delay of growth process.At booting stage,the wall thickness and stem fullness of stem can be significantly increased by applying fertilizer.Under the same treatment at the same time,the wall thickness and fullness of stem at different internodes decreased successively from the internodes at the base and the difference was significant.standing to jointing stage: booting stage: 1:1 fertilizer not only ensures enough tiller number,but also provides sufficient nutrition for later grain filling and improves the fullness of stem.2.Effects of nitrogen fertilizer timing on stem mechanical characteristics of wheatWith the help of the stem strength tester,three stages were selected,namely anthesis stage,filling stage,maturity stage,to measure the breaking strength at each node of the stem of the two varieties.The results showed that the breaking strength of stem was T1>T3>T2>CK in the filling stage and maturity stage and T1> CK> T2 and T3 in the anthesis stage.At maturity stage,T1 treatment at the second internode of SN16 at the base was 36.47%,21.07% and 18.82% higher than other treatments;JM22 T1 treatment was 20.13%,16.67%and 9.87% higher than other treatments(the average of the two years).Lodging resistance varieties of each internode stem lodging breaking strength is significantly higher than sensitive varieties,different internodes upward from the base breaking strength is abate,in turn stem breaking strength with the development of growth timing was increased then reduced,reach the maximum breaking strength in filling stage.Correlation analysis showed that the stem enrichment degree and breaking strength was significantly positively related.3.Effects of nitrogen fertilizer on lignin metabolism in wheat stalksThe accumulation of lignin in anthesis stage,filling stage and maturity stage,the expression of key enzyme gene in lignin synthesis pathway,the activity of starting enzyme in lignin synthesis pathway and the deposition amount and rule of three monomers weremeasured.The results showed that the lodging resistance varieties of lignin accumulation was significantly higher than that of lodging sensitive varieties,from anthesis stage to maturity stage of lignin accumulation and three kinds of monomers precipitation amount has been increasing,amount of lignin synthesis pathway gene expression of key enzyme to reduce gradually,lignin synthesis pathway of initial enzyme activity has also been gradually reduced,T1 treatment can increase the stem each internode lignin accumulation of the sum of the three kinds of monomers.Taking the second internode at the base of maturity stage as an example,S monomer increased by 13.01%,25.62% and 5.55% in the second internode T1 treatment of SN16 compared with CK,T2 and T3,and 24.62%,11.34% and 11.22% in the T1 treatment of JM22 compared with CK,T2 and T3.Booting stage,anthesis stage fertilization can slow down the stem each internode from anthesis to filling stage and filling stage to the maturity stage of lignin accumulation is reduced.All the fertilizer in jointing stage was not conducive to lignin synthesis in later growth timing,and the breaking strength of stem was reduced.The accumulation of lignin,s-type lignin monomer,g-type lignin monomer and the sum of the three monomers decreased from the basal internode to the stem.This indicated that the nitrogen fertilizer timing had a significant effect on the lignin synthesis pathway and metabolites in the culm.Under the condition of population densification,the purpose of improving the quality of stem and enhancing the lodging resistance of the whole stem of wheat can be achieved in the timing of applying rational topdressing nitrogen fertilizer.4.The effect of nitrogen fertilizer timing on wheat yieldReasonable nitrogen fertilizer timing can significantly increase wheat yield.Under different topdressing conditions in this experiment,topdressing at booting stage can significantly increase the 1000-grain weight of wheat at harvest,and the yield is the highest at T1(standing to jointing stage : booting stage 1:1),SN16 T1 treatment was 7.47%,4.37% and5.49% higher than other treatments;JM22 T1 treatment was 9.97%,6.58% and 12.59%higher than other treatments(the average of the two years).Although the 1000-grain weight of T3(all topdressing in booting stage)treatment was higher,the yield of T3 was lower than that of T1 due to the late topdressing timing and the small number of panicle formed by plants,indicating that late fertilization was not conducive to the improvement of yield. |
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