Formation Mechanism And Regulation Measures Of Inferior Grain Of Buckwheat

In order to clarify the physiological mechanism of the formation of inferior spikelet of buckwheat,and put forward the cultivation measures to promote the filling of inferior spikelet,this research through setting up different nitrogen fertilizer application,removing the apical dominance and chemical regulatory substances treatment.The effects of buckwheat on root morphology and physiology,photosynthesis and assimilate transport,endogenous hormone content,filling characteristics of strong and weak grains,key enzyme activities of sucrose-starch metabolism pathway and final yield formation were studied.The main research contents are as follows:（1）Difference of grain filling characteristics and starch synthesis between the superior and inferior spikelet of Tartary buckwheatIn this research,Tartary buckwheat（Fagopyrum tataricum Gaertn）“cv Jinqiao 2”（JQ2）was used to determine the difference among grain filling characteristics,starch and starch synthesis enzyme activities,and photosynthetic characteristics between superior and inferior spikelet and to clarify the physiological mechanism of the formation of inferior spikelet of Tartary buckwheat.The initial growth power（R₀）,maximum grain filling rate(G_max),and average grain filling rate(G_mean)of superior spikelet were remarkably higher than those of inferior spikelet,whereas the time required to reach the maximum grain filling rate(T_max.G)was lower than that of inferior spikelet.The contribution rate to grain weight in the middle filling stage was the largest,followed by the later filling stage and the smallest in the early filling stage of superior spikelet.The contribution rate of the middle filling stage was the largest,followed by the early filling stage,and the smallest was the late filling stage of inferior spikelet.The starch content and net photosynthetic rate of superior spikelet were higher than those of inferior spikelet.The activities of adenosine diphosphate glucose pyrophosphate and soluble starch polymerase in the superior spikelet at the early filling stage were stronger than those in the inferior spikelet but lower than those in the inferior spikelet in the middle and late filling stages.In summary,low light energy utilization and biosynthesis activity at the early filling stage,andinsufficient supply of photosynthetic substances in late leaves are important physiological conditions for the low grain filling rate and the light grain weight of inferior spikelet.（2）Effect of nitrogen fertilizer application on grain filling of superior and inferior spikelet and yield of Tartary buckwheatThe poor grain filling and small grain weight of the inferior spikelet limit the yield potential of crops.The main objective of this study was to clarifying the formation mechanism of the inferior spikelet as well as putting forward cultivation techniques to promote the filling and enrichment of the inferior spikelet.Four nitrogen fertilizer applications on Tartary buckwheat（Fagopyrum tataricum Gaertn）“cv Jinqiao 2”to determine their effects on grain filling characteristics,starch synthase activities,photosynthetic characteristics,antioxidant enzyme activity,and malondialdehyde（MDA）of superior and inferior spikelet.We found that the time to reach the maximum grain filling rate(T_max.G)was the shortest for the middle nitrogen fertilizer application treatment（N2）,while the maximum grain filling rate(G_max)and average grain filling rate(G_mean)were the highest.The A value,initial growth power（R₀）,G_max,and G_meanof the superior spikelet were higher than those of the inferior spikelet,whereas its N values and T_max.G were lower.The activity of starch synthase was strong under N2.The activities of glucose pyrophosphorylase and soluble starch synthase in the superior spikelet at the early filling stage were stronger than those in the inferior spikelet but lower than those in the inferior spikelet at the middle and late filling stages.The photosynthetic characteristics and antioxidant enzyme activity were the strongest in N2 and the superior spikelet,while MDA content was the lowest.In summary,starch biosynthesis activity in the early filling stage and insufficient supply of photosynthetic substances in late leavesare important physiological factors for the low grain filling rate and light grain weight of the inferior spikelet.Suitable nitrogen fertilizer application can delay premature senescence,enhance photosynthetic efficiency,promote grain filling of the superior and inferior spikelet,and increase grain weight and final yield.（3）Effect of apical dominance removal on the inferior spikelet formation of common buckwheatThe poor grain filling and light grain weight of the inferior spikelet limit the yield potential of crops.This study aimed to assess the effect of apical dominanceremovalon the inferior spikeletformation of commonbuckwheat.The differences in grain filling characteristics,starch and starch synthesis enzyme activities,endogenous hormone content,root morphology and physiology,leaf antioxidant enzyme activity,agronomic characteristics,and yield formationof common buckwheat（Fagopyrum esculentum Moench）‘cv.Fengtian 1’（FT1）treated with and withoutapicaldominanceremoval（RA and NRA,respectively）.Compared with the NRA group,the RA group had remarkably higherinitial growth power（R₀）,maximum grain filling rate(G_max),and average grain filling rate and lower time required to reach the G_max(T_max.G).The contribution rate to grain weight of the RA and the NRA treatments followed the order:middle filling stage>later filling stage>the early filling stage.The starch synthesisactivitiesoftheinferior spikelet of FT1 increased first and then decreased with the growth period.The RA grouphad higher starch synthesis activities,stronger antioxidant enzyme activity,higherroot morphology and root activities,and lower malondialdehyde content than the NRA group.The contents of abscisic acid（ABA）and indo-3-acetic acid（IAA）in the inferior spikelet of FT1 increased first and then decreased with increasinggrowth stage,whereas the gibberellins（GA₃）content continued to decrease.The RA group had higher ABA and IAA contentsin the inferior spikeletand lower GA₃ content than the NRA group.The number of main stem branches andgrains per plant,grain weight per plant,1000-grain weight,and yield in the RA group were higher than those in the NRA group.In summary,high starch synthesis activity,high ABA and IAA contents,and low GA₃ content accounted for the increased grain weight and filling rate of inferior spikeletin the RA treatment.（4）Effects of exogenous strigolactone and strigolactone inhibitor on the non-structural carbohydrate remobilization and grain filling of Tartary buckwheatStrigolactone is a important new hormone that regulates plant growth and development and resource allocation.This study aimed to clarify the physiological mechanism of strigolactone regulating grain filling,non-structural carbohydrate（NSC）remobilization,and yield formation of Tartary buckwheat.The Tartary buckwheat‘cv Jinqiao 2’was used as experimental material to study the effects of exogenous strigolactone and its inhibitor（Tis108）on the grain filling of superior and inferior grains,NSC remobilization,and yield formation of Tartary buckwheat.Compared with the control,the exogenous strigolactone treatment could promote the grain filling of inferior grains at the early grain filling stage and the contribution rate of NSC in grain shell to grain yield.However,the treatment of exogenous strigolactone decreased the soluble starch synthase and adenosine diphosphate glucose scorphosphorylase activities in superior grains,the SOD and POD activities in leaves,transport of NSC in leaves to superior grains,and final yield of Tartary buckwheat and inhibited the grain filling of superior grains.The application of Tis108 promoted the grain filling of superior and inferior grains at the late grain filling stage,increased the activity of starch synthase in superior grains,promoted the transport of NSC from leaves to grains,increased the activities of SOD and POD in leaves,and increased the grain number per plant and final yield.In conclusion,Tis108 treatment could promote grain filling,delay senescence,and improve the final yield of Tartary buckwheat.The T10 treatment had a good application prospect in Tartary buckwheat production.