Study On The Regulation Technology Of Nitrogen Fertilizer Level On Young Spike Differentiation Of Wheat With Different Spike Types

Increasing the number of wheat grains per spike is one of the important goals and measures of wheat high yield cultivation.As an important process of yield formation,young spike differentiation of wheat determines the number of spikelets,number of florets,fruity and kernel number per panicle.Spikelets are considered to have high heritability,but are sensitive to cultivation environment.Therefore,the multi-spike wheat variety Ji Mai 22（JM22）and the large-spike wheat variety Tai Nong 18（TN18）were selected as test materials in this experiment,and three nitrogen fertilizer levels were set,namely 120 kg ha^-1（N1）,240kg ha^-1（N2）and 360 kg ha^-1（N3）.this study studied the regulation effect of nitrogen fertilizer level on the differentiation process of young spikelets of wheat,In order to provide theoretical basis for the regulation of spikelets and grains per spike,and to provide technical support for high-yield cultivation of wheat.The main research results are as follows:1.Effects of nitrogen fertilizer level on wheat yield and its component factorsThe number of spikelets of two wheat varieties increased with the increase of nitrogen fertilizer application rates.However,the number of grains per spike of the two varieties reached the maximum at the nitrogen application rate of 240 kg ha^-1,which was significantly higher than that of the other two treatments.The 1000-grain weight of the two varieties decreased gradually with the increase of nitrogen nitrogen fertilizer application rates,and N1treatment was significantly higher than the other two treatments.The yield of multi-spike type JM22 was 9547.52 kg ha^-1at the nitrogen application rate of 360 kg ha^-1.However,the yield of large spike type TN18 was higher at 240 kg ha^-1and 360 kg ha^-1nitrogen application levels,and there was no significant difference between the two nitrogen application levels.2.Effects of nitrogen fertilizer level on spikelets per ear of wheatThe number of spikelets per spike of two different types of wheat was significantly affected by nitrogen fertilizer level,which firstly increased and then decreased with the increase of nitrogen application rate,and reached the maximum under the nitrogen application rate of 240 kg ha^-1,and the levels of the three types of nitrogen were N2>N3>N1.The spikelets per spike of JM22 and TN18 treated with N2 and N3 were 8.6%,6.7%and 6.2%,4.9%higher than those treated with N1,respectively.Under the same nitrogen fertilizer level,TN18 was significantly higher than JM22,and the number of spikelets per spike of TN18under N1,N2 and N3 treatments was 5.6%,6.3%and 8.0%higher than that of JM22,respectively.3.The effect of nitrogen fertilizer level on the differentiation process,ergodic days,and morphological characteristics of young paniclesThe increase of nitrogen fertilizer rate could accelerate the process of spike differentiation and shorten differentiation time.The beginning time of differentiation of floret primordium under each treatment was N3>N2>N1,The elapsed days of TN18 were greater than 2 days that of JM22 in the central to final double ridge stage.From the final double ridge stage to the differentiation stage of protective primordium JM22,the number of elapsed days of TN18 under N2 was the same,while the elapsed days number of TN18 under N2 was 2days longer than that of N1 and N3.With the increase of nitrogen fertilizer,spike differentiation elapsed days of the two varieties decreased gradually,and the elapsed days number under N1,N2 and N3 treatments was 18,16 and 14 days.The length and width of young spike in the three stages of differentiation after the middle of the second row increased first and then decreased with the increase of N application rate,and reached the maximum when N application rate was 240 kg ha^-1.TN18’s length was significantly greater than that of JM22,but there was no significant difference in width between the two varieties.4.Effects of nitrogen fertilizer level on endogenous hormone content and ratio in spikelets during young spike differentiationThe content of GA₄and ZR in young spikelets of the two varieties increased firstly and then decreased with the increase of amount of nitrogen fertilizer.The ratio of GA₄/ABA and ZR/ABA increased with the increase of nitrogen fertilizer at the central to final and front of double ridge stage,respectively.The ratio of GA₄/ABA and ZR/ABA increased first and then decreased in other periods,reaching a maximum nitrogen application rate of 240 kg ha^-1.The ratio of TN18 to two hormones is greater than JM22.ABA showed a gradual decline with the increase of nitrogen fertilizer.Correlation analysis of hormone content and ratio with spikelet number revealed that,in addition to ABA and the number of spikelets.were significantly and negatively correlated,the other hormone content and ratio were significantly and p significant positively correlated with spikelet number.This result suggests that it is possible to reduce the ABA content and increasing GA₄and ABA content is conducive to the increase of spikelet number.5.Effect of nitrogen fertilizer level on the gene relative expression in spikelets during young spike differentiationThe amount of nitrogen fertilizer affected the relative expression of related genes in the process of young spike differentiation,and then affected the number of spikelets.The expression of FUL2 and VRN1 genes increased gradually with the improve of nitrogen application,while the transcription levels of VRT2 and SPL17 showed an upward and downward trend,and the transcription levels were strongest under N2.The relative expression levels of the four genes mentioned above all showed that TN18 was greater than JM22.VRS1expression showed an overall trend of"V"shape,with the lowest transcription level under N2.The VRS1 expression level of JM22 is higher than that of TN18.The correlation analysis between the gene expression level and spikelet number revealed that,VRS1 expression was significantly negatively correlated with the number of spikelets,while the expression level of other genes was significantly positively correlated with pikelet number.The results indicated that lowering VRS1 and increasing the transcription level of the other four genesfavors an increase of the number of spikelets.6.Effects of nitrogen fertilizer levels on the contents of soluble sugar and protein in leaves during young spike differentiationWith the increase of nitrogen fertilizer,the contents of fructose,sucrose,glucose and soluble protein all showed a trend of first increasing and then decreasing,which were manifested as N2>N3>N1 and there were significant differences.The content of three soluble sugars in TN18 was higher than that in JM22,and the opposite is true of soluble protein.The suitable nitrogen fertilizer input not only had a significant effect on the content of soluble sugar in leaves during young spike differentiation,but also had a significant relationship with the content of soluble protein in leaves.In conclusion,Nitrogen application of 240 kg ha^-1promoted the accumulation of GA₄and ZR in panicle at front and central double ridge stage of wheat,and increased the ratio of GA4/ABA and ZR/ABA in the early and middle panicle of the second row.The transcriptions of FUL2 VRN1 and SPL17 and VRT2 were increased in the central to final of double ridge stag,and the transcriptions of VRS1 in the whole double ridge stage were decreased.Prolongs the days of differentiation,increases the length and width of young spike,promotes the formation of spikelet primordium.The contents of soluble sugar and soluble protein in functional leaves of wheat were increased,and sufficient nutrients were provided to ensure the smooth progress of young spike differentiation,thus increasing the number of spikelets.