Effects Of Heat Stress During Grain Filling On Grain Yield And Starch Quality Under Different Nitrogen Levels Of Waxy Maize

The experiments were carried out in 2015-2016 in experimental farm and intelligent greenhouses of Agricultural College,Yangzhou University.The response of waxy maize grain yield and starch quality under different nitrogen(N)levels(N topdressing at jointing stage were 0,5 and 10 g/pot for pot trial and 0,150 and 300 kg/ha for field trial,named as N1,N2 and N3,respectively)to heat stress during grain filling was studied using Suyunuo5 and Yunuo7 as materials.The main results were as follows:1.Effects of heat stress during grain filling on grain yield and starch quality under different N levelsHeat stress during grain filling decreased the grain yield significantly,and the value rose first and falls later under different temperature(ambient and high temperature)conditions with the increase of N topdressing amount at jointing stage.Heat stress decreased the soluble sugar and starch content and increased protein content.With the increase of N topdressing,protein content under both ambient and high temperature conditions increased gradually;the soluble sugar content decreased gradually under ambient temperature condition and falls first and rose later under high temperature condition,respectively.The starch content rose first and fall under high temperature condition and the value was similar among three N levels under ambient temperature condition.Heat stress increased the starch iodine binding capacity,and the value under both ambient and high temperature conditions rose first and falls later with the increase of N topdressing amount.The starch granule size was increased by heat stress,and the value gradually decreased and rose first and falls later under high and ambient temperature conditions,respectively.Heat stress decrease the peak,trough,final and breakdown viscosities and increase the setback viscosity and pasting temperature of waxy maize flour.The starch peak viscosity under N2 condition was increased and the value under N1 and N3 conditions was decreased by heat stress,respectively.The breakdown viscosity under both N1 and N2 levels was not affected by heat stress and the value under N3 level was decreased by heat stress.With the increase of N topdressing,the peak and breakdown viscosities for flour and starch were decreased gradually under ambient temperature condition and the two values rose first and fall later under high temperature condition,respectively.The gelatinization temperatures of flour and starch(onset,peak and conclusion temperature)under different N levels were increased by heat stress.The flour gelatinization enthalpy under N3 level was not affected and the value under N1 and N2 levels was increased by heat stress,respectively.The starch gelatinization enthalpy under N1 level was increased and the value under N2 and N3 levels was decreased by heat stress,respectively.The retrogradation percentage of flour under different N levels was increased by heat stress.The retrogradation percentage of starch under N1 and N2 levels was increased and it under N3 level was decreased by heat stress,respectively.With the increase of N topdressing,the retrogradation percentage of flour was similar between N1 and N2 levels and higher than N3 level under ambient temperature condition;the value under high temperature condition was similar between N2 and N3 levels and higher than N1 level.The starch retrogradation percentage falls first and rose later with the increase of N topdressing under both ambient and high temperature conditions.2.Effects of sown date on grain yield and starch quality under different N levelsThe grain number,weight and yield rose first and fall later with the increase of N topdressing under different sown dates.Those three parameters were higher under S2 of spring sown dates,while grain weight and yield were higher under S3 and the grain number was high under S4 of summer sown dates.With the increase of N topdressing,the protein and starch content rose first and fall later under normal temperature(average value of two varieties under S1 and S4 treatments).Under high temperature(average value of two varieties under S2 and S3 treatments),the protein content was increased by N topdressing but no difference was observed between N2 and N3,while starch content increased gradually with the increase of N topdressing.The blue value,maximum absorption wavelength and iodine binding capacity was higher under S2 and S3 treatments under spring and summer sown dates,respectively,in consistent with the pot trial.The starch granule size was higher under S1 and S3 under spring and summer sown dates,respectively.With the increase of N topdressing,the iodine binding capacity and granule size of starch rose first and fall later under both temperature treatments.Under spring sown dates,the flour peak and breakdown viscosities for Suyunuo5 were higher at S2,the breakdown viscosity of Yunuo7 also higher at S2,while peak viscosity was lower at S2,respectively.The starch peak and breakdown viscosities for both varieties were higher at S1.All pasting characteristics under summer sown dates were higher at S3.Under normal temperature conditions,with the increase of N topdressing,the flour peak and breakdown viscosities were higher under N1 level and no difference between N2 and N3,while the starch peak and breakdown viscosities were lower under N3 level and no difference between N2 and N1.The peak and breakdown viscosities gradually decreased with the increase of N topdressing under both temperature conditions.The retrogradation percentage of flour and starch was high under S2 and S3 treatments under spring and summer sown dates,respectively.Under normal temperature condition,the retrogradation percentage of flour rose first and fall later,while the value of starch fall first and rose later,with the increase of N topdressing.Under high temperature condition,the retrogradation percentage of flour was lower under N3 and no difference between N1 and N2,while value of starch was high under N1 and no difference between N3 and N2.