Study On The Regulation Effect And Physiological Basis Of Delayed Sowing Date On The Development Of Spike And Floret Of Winter Wheat

The field experiments were carried out in 2014-2015 and 2015-2016 at the experimental station of Dongwu Village,in Dawenkou Town,Daiyue District,Tai?an,Shandong,P.R.China.Two widely planted cultivars,Tainong 18（a cultivar with bigger ears）and Jimai22（a cultivar with middle-sized ears）,were selected as the experimental materials（henceforth referred to as“T18”and“J22”,respectively）and sown in a field on five dates（24 September and 1,8,15,and 22 October）.The studies were focused on the regulation effect of delayed sowing dates on the floret development and grain set of winter wheat.The relationship between floret development and accumulation and distribution of assimilates during florets development was discussed.The result elucidated the change in the endogenous hormones levels in the different spikes and stems during floret development,and explored the relationship between endogenous hormone contents and its balances and accumulation and distribution of assimilates,and clarified the regulation mechanism of endogenous hormone changes on the accumulation and distribution of assimilates.The main results are shown as follows:1.Effect of delayed sowing dates on the grain yield and related components in winter wheatDelayed sowing significantly reduced the number of spikes per unit area,but increased the number of grains per spike,while there was no significant difference in grain weight among sowing dates.The maintenance of grain yield was due mainly to the similar proportions of decreased spikes per square meter and increased grains per spike.It can be seen that the maintenance of high yield is mainly due to the increase of grain number per spike.The effect of delayed sowing date on the growth and development of winter wheat population was significant before the jointing stage.With the advancement of the growth process,the difference among sowing dates gradually decreased.The number of shoots per unit area,leaf area index and dry matter accumulation per unit area of winter wheat before the jointing stage were significantly different among treatments.After the jointing stage,the gaps in the number of shoots per unit area and leaf area index and the accumulation of dry matter were significantly reduced.The sowing date changed the population structure of winter wheat,and the delayed sowing date reduced the number of tillers before winter,but increased the number of tillers in spring,and the ratio of before winter tillering to spring tillering increased significantly.Both the number of effective tillers and ineffective tillers was reduced with delayed sowing date.However,the number of ineffective tillers decreased significantly,so the ratio of effective tiller to ineffective tiller was increased.The rate of tiller survival before winter and whole growth period were significantly increased with delayed sowing date,and increase in the rate of tiller survival before winter was more significant.Obviously,delaying the sowing date increases the proportion of the main stem,and reduces the proportion of effective tillers in the group at the maturity period.Delayed sowing period increased the translocation and translocation rate of dry matter stored in vegetative organs before anthesis and the contribution to grain yield,but the dry matter accumulation and the contribution to grain yield after anthesis of wheat plants decreased.Delayed sowing date reduced the amount of above-ground nitrogen uptake,which led to decrease nitrogen uptake efficiency,but the nitrogen utilization efficiency was significantly improved.There was no significant difference in nitrogen use efficiency and nitrogen harvest index among treatments;The grain nitrogen concentration decreased,but the nitrogen production efficiency increased significantly with delayed sowing date,indicating that the late sowing treatment increased the ability to utilize the nitrogen absorbed by the wheat for grain production,and reduced the nitrogen demand required for the production of unit mass of grain.Delayed sowing significantly reduced nitrogen translocation in vegetative organs and nitrogen uptake after anthesis,but increased nitrogen translocation efficiency in vegetative organs and contribution to grain nitrogen after anthesis,indicated that winter wheat with delayed sowing date has strong nitrogen translocation and redistribution capacity.2.Effect of delayed sowing dates on the differentiation characteristics of florets in spikesDelayed sowing date resulted in a decrease in the maximum number of florets per spike,while the number of fertile florets per spike and the number of grains per spike increased,and the setting rate and survival rate of florets were significantly improved.There was no significant change in the setting rate of fertile floret.With the delay of the sowing date,the average differentiation rate increased significantly,while the average degeneration rate showed the opposite.The sowing date caused significant differences in the maximum number of florets by affecting the differentiation rate of florets and the duration of differentiation.The degenerated duration is not affected by the change of sowing date,so the decrease of the average rate of degradation is the reason for the decrease in the degenerated number of floret,and also the guarantee for the improvement of the survival rate of florets.Correlation analysis showed that the number of grains per spike was significantly positively correlated with the number of fertile florets,the survival rate of florets and the setting rate of florets,but the correlation between total number of spikelets and the maximum number of differentiated florets and grain number per spike did not reach a significant level.The increase in the number of grains per spike is achieved through increasing both the number of fertile florets per spike and the survival rate and the setting rate of florets.3.Effect of delayed sowing dates on the accumulation and distribution of assimilatesThere was a significant positive correlation between the number of fertile florets at anthesis and the dry weight of spike,the ratios of dry matter and nitrogen between spikes and stems,which indicated that the survival number of fertile florets at anthesis was not only related to the total dry matter supply for spike,but also related to the distribution of dry matter in the spikes and stems.Delayed sowing significantly increased the distribution of ¹³C assimilates,water-soluble carbohydrates and nitrogen in the spikes and the corresponding ratio of spikes to stems.Delayed sowing date resulted in decrease in water-soluble carbohydrate content and C/N ratio in spikes,and an increase in nitrogen content during the process of floret differentiation.However,delayed sowing date significantly increased the water-soluble carbohydrate content in the panicle and C/N ratio,while the nitrogen content is significantly reduced during the stage of floret degradation.Correlation analysis showed that the number of fertile flowers per spike and the average differentiation rate of floret were positively correlated with the distribution ratio of water-soluble carbohydrates and nitrogen and the corresponding ratios of spikes to stems,which was positively correlated with the nitrogen content during floret differentiation process,indicating that nitrogen metabolism is beneficial to the differentiation of florets.The number of fertile flowers is positively correlated with the content of water-soluble carbohydrates and C/N ratio during the process of floret degradation,while the average degenerated rate was negatively correlated with the content of water-soluble carbohydrates and C/N ratio in the spike during floret degeneration,indicating that carbon metabolism is beneficial to floret development and decrease in the floret degeneration,and a higher C/N ratio is beneficial to the survival of florets.4 Effect of delayed sowing dates on the levels and balance of endogenous hormones in spikes and stemsThe contents of endogenous hormones indole-3-acetic acid（IAA）,gibberellic acid（GA₃）,zeatin riboside（ZR）and zeatin in the spikes increased with the delay of the sowing date,while the abscisic acid（ABA）content showed a downward trend.The GA₃/ABA,IAA/ABA and（ZR+zeatin）/ABA ratios in the spikes all increased with the sowing date,indicating that delayed sowing date was beneficial to increase in GA₃/ABA,IAA/ABA and（ZR+zeatin）/ABA ratios increase in the spikes..In addition,the ratios of contents of GA₃,IAA,ZR and zeatin between spikes and stems also increased with the delay of the sowing date,while the ABA showed the opposite.Correlation analysis showed that the number of fertile florets at anthesis was positively correlated with the contents of GA₃,IAA,ZR and zeatin in the spikes and the corresponding ratios between spikes and stems and GA₃/ABA,IAA/ABA and（ZR+zeatin）/ABA ratios,but negatively correlated with the ABA content in the spikes and the corresponding ratio between spikes and stems.This shows that in the present study,the higher the contents of GA₃,IAA,ZR and zeatin and the lower the ABA content,the more the number of grains.The higher contents of GA₃,IAA,ZR and zeatin and lower ABA content in spikes are important physiological basis for the formation of more grains.Moreover,higher GA₃/ABA,IAA/ABA,and（ZR+zeatin）/ABA ratios are beneficial to survival of more fertile flowers.In addition,the distribution of the ¹³C assimilates and the water-soluble carbohydrate content in spikes were positively correlated with the levels of IAA,GA₃,ZR+zeatin and the corresponding ratios between spikes and stems and IAA/ABA,GA₃/ABA,（ZR+zeatin）/ABA ratios.However,there was a negative correlation between the ABA content in the spikes and the distribution of the ¹³C assimilates and the water-soluble carbohydrate content in the spikes and the corresponding ratios between spikes and stems.This indicates that higher contents of GA₃,IAA,ZR and zeatin in the spikes and higher ratios of GA₃/ABA,IAA/ABA and（ZR+zeatin）/ABA facilitate the transport of more assimilates into the spikes.The lower ABA content and the corresponding ratio between spikes and stems can alleviate the inhibition of assimilates into the spikes and provide favorable conditions for the survival of more fertile florets.