Effects Of Stagnant Flooding On Growth,Yield And Grain Quality Of Rice Genotypes And Associated Physiological Mechanism At Different Growth Stages

In southern rice production area in China,flooding stress occurs constantly due to precipitation frequently in summer,and caused yield great loss.Rice can encounter flooding stress at any growth periods,and the flooding-tolerance of rice is different at different growth stages.In recent years,the yield potential of newly bred rice varieties has gradually increased,but the flooding-tolerance performance is poorly improved.The capacity of flooding-tolerance is big differences among rice genotypes.Several studies have reported the effect of flooding stress on growth and physiological traits of rice,but mainly focused flooding stess imposed on several rice genotypes at one of growth stage,or on some growth stages with single rice genotype.However,the effects of stagnant flooding(SF)imposed at different key growth stages(TF(SF at tillering stage),PF(SF at panicle initiation stage),HF(SF at heading stage),TF+PF+HF)on the growth,yield and rice quality of different genotypes of rice are rare studied.Therefore,this study aimed to use different rice genotypes(conventional indica rice-HHZ,conventional japonica rice-WYG3,indica hybrid rice-YLY900,japonica hybrid rice-YY4949,Sub1-introduced rice genotype-IR64-Sub1)as experimental materials which imposed to simulate stagnant flooding at different growth stages to study the followings:the characteristics of growth,endogenous hormones,energy metabolism,reactive oxygen metabolism,osmoregulation substances,yield performace and yield components,grain quality of rice genotypes response to stagnant flooding stress.The purposes of this study were to reveal the related physiological mechanism of rice response to flooding stress.The main experiment results as follows:(1)Effects of stagnant flooding on the growth traits of rice genotypesThe leaf area index,leaf biomass,stem biomass,total biomass,crop growth rate,and tiller number of rice genotypes decreased significantly under SF at each growth stages,but specific leaf weight increased significantly.At tillering stage,plant height of each rice genotype increased significantly under SF,with an average increase by 20.9%.On the contrary,plant height was decreased significantly at panicle initiation stage and heading stage under SF,with a decrease by 8.9%and 12.8%average the two year,respectively.Overall,SF at each growth stage(TF,PF,HF,TF+PF+HF),the leaf area index was decreased by 53.8%,24.3%,16.2%,and 45.7%,biomass decreased by 66.7%,48.4%,16.5%and 55.4%,crop growth rate decreased by 66.1%,45.5%,19.6%and 55.1%,tiller number decreased by 59.5%,26.9%,22.2%and 56.9%,but specific leaf weight(SLW)increased by 26.8%,26.5%,1.9%and 0.9%,respectively.Among of them,WYJ 3 showed the worst growth performance under SF,which showed the hieghtest plant height increase by 29.3%at TF,and the maximum decrease of tiller numbr and leaf area index by 33.2%and 33.6%at PF,respectively,and the maximum of tiller number,leaf biomass,stem biomass,total biomass,and crop growth rate by 26.5%and 64.7%,16.3%and 57.1%,29.3%and 69.2%,26.4%and 66.6%,and 30.1%and 68.1%at HF and TF+PF+HF,respevtively.Based on the responses of various growth indicators to SF,WYJ 3 was more sensitive to SF than other rice varieties.(2)Effects of SF on endogenous hormones at early tillering stageThe concentration of ethylene was significantly increased under SF,which increased by 169.3%on average compared with control.In addition,the increase in ethylene resulted in an increase in auxin(IAA)and gibberellin(GA3)concentrations,but decreased in abscisic acid(ABA)and cytokinin(Z,ZR,IPA).Compared with the control,the IAA and GA3 were average increased by 19.7%and 38.0%,respectively,while ABA,Z,ZR,and IPA decreased by 19.2%,9.2%,28.4%,and 9.5%,respectively.Among the genotypes,the contents of auxin and gibberellin in WYJ 3 were significantly higher under SF,and increase by 137.0%and 239.2%,respectively.The results suggest that rice tillering inhibited under SF is attribute to the imbalance of endogenous hormones.(3)Effects of SF on energy metabolites in riceThe content of chlorophyll and NSC(non-structural carbohydrate)of each rice genotype was significantly reduced under SF,and the decrease was more aggravated in more than once SF stress.On average,the contents of chlorophyll and NSC rice was decreased by 60.2%and 40.5%under SF at TF,decreased by 37.4%and 29.5%at PF,decreased by 11.4%and 27.1%at HF,and decreased by 40.3%and 33.8%at TF+PF+HF,respectively.Except at TF,YLY900 showed the highest chlorophyll content but WYJ3 was the lowest,the maximum content of NSC was produced by YLY 900 but the minimum NSC was showed by HHZ.(4)Effects of SF on antioxidant enzymes in riceThe activity of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)in rice leaves was increased significantly under SF,and the increase was more aggravated by SF frequence.The contents of SOD,POD and CAT in rice leaves increased by 69.2%,136.5%and 66.8%respectively under TF,increased by 151.8%,106.8%and 195.8%under PF,increased by 49.3%,111.4%and 147.0%under HF,and increased bu 81.2%,144.4%and 266.2%under TF+PF+HF,respectively.The highest activity of antioxidant enzymes was produced by YLY 900 under SF at all growth stages except at TF.(5)Effects of SF on osmotic regulator substances in ricethe content of MDA,Pro and soluble protein in rice leaves was increased significantly under SF,and the increase was more aggravated by SF frequency.The content of MDA,Pro and soluble protein in rice leaves increased by 136.5%,52.8%and 40.9%under TF,and increased by 500.4%,95.5%and 135.0%under PF,increased by 613.2%,69.2%,and 170.3%at HF,and increased by 915.4%,101.1%,and 227.4%at TF+PF+HF,respectively.At PF,HF and TF+PF+HF,YLY 900 showed the lowest MDA content,but the highest Pro and soluble protein content than other genotypes.(6)Effects of SF on grain yield and yield componentsPanicles,spikelets per panicle,grain filling,grain weight,biomass and HI of rice genotypes were significantly decreased udner SF.On average,panicle number decreased 34.7%(ranged from 11.1%to 66.2%),spikelets per panicle decreased 21.7%(ranged from 6.4%to 40.1%),grain weight decreased by 8.6%(ranged from 1.7%to 16.2%),which eventually led to yield great loss(average decreased by 34.3%,and ranged from 11.0%to 75.4%).The effect of flooding stress on yield loss at each period was showed T5(average decreased by 48.8%)>T2(average decreased by 39.0%)>T3(average decreased by 29.3%)>T4(average decreased 20.0%).The yield loss was seriously under TF than under PF and HF.The yield decrease was mainly caused by reduction in panicle number under TF,and caused by decreased in spikelets per panicle,grain filling and grain weight under PF and HF,and caused by all yield components decline under TF+PF+HF.Under TF+PF+HF,panicles,spilelets per panicle,grain filling and grain weight was decreased by 54.6%,30.5%,29.3%,13.7%,respectively.Among the genotypes,WYJ 3 showed the largest yield decrease under each treatment,with an average decrease of 64.2%,53.5%,39.6%,and 73.8%,respectively.On the contrary,IR64-Sub1 showed the lowest yield decrease,with an average decrease of 26.6%,18.5%,9.9%,and 36.3%,respectively.(7)Effects of flooding stress on grain quality of riceThe rice quality of each genotype was significantly decreaded under SF.The milling quality of brown rice,milled rice and head rice were decreased by 4.4%,5.6%,and 6.5%on average under SF.The appearance quality of grain length and grain width were decreased by 3.4%and 4.2%,and the chalkiness rate and chalkiness increased by 102.3%and 302.3%on average under SF.The cooking and eating quality of appearance,taste value,texture,hardness,viscosity and balance of rice decreased by 15.0%,13.4%,13.6%,14.5%,9.7%and 16.0%,respectively.Among the treatments,recall the grain quality paramters(except milled and head rice)were decreased more sharply under TF+PF+HF.Under TF+PF+HF,the brown rice decreased 5.3%,grain length and grain width decreased 5.0%and 6.0%,respectively.The chalkiness rate and chalkiness increased by 164.3%and 488.4%.The appearance,taste,texture,hardness,viscosity and balance of rice decreased by 19.8%,21.6%,19.8%,21.8%,25.6%,40.8%,respectively.In addition,it was found that the grain quality was worse at panicle initiation stage and heading stage than tillering stage under SF.(8)Correlation analysisCorrelation analysis showed that the LAI,biomass,chlorophyll and NSC of each genotype were significantly positively correlated with grain yield under SF.Therefore,genotypes with these traits such as high LAI,high biomass production,high chlorophyll and NSC content can be screened as the SF-tolerant rice line or genotype.(9)Flooding-tolerance difference of rice genotypesThe capacity of SF-tolerance of rice genotypes could be preliminary devided as V3(YLY 900,indica hybrid rice)>V4(YY 4949,japonica hybrid rice)>V5(IR64-Sub1)>V1(HHZ,indica conventional rice)>V2(WYJ 3,japonica conventional rice).according to the performance of growth,physiology,yield and quality under flooding stress.