Study Of Drought Resistance Mechanism And Identification Parameters Screening In Maize

Study the impact of different periods of drought on maize growth and development, physiological and biochemical characteristics by the combination of field experiments and pot environment;Study the relationship between various physiological indicators;Compares the resistant differences exist amoung varieties;Explore the relationship between physiological and biochemical indicators and drought resistance of maize,and make mechanisms for drought resistance clear;Determine the indicators of resistance evaluation of crop drought; Set up a optimize index system with scientific and accurate evaluation of maize drought resistance to provide theoretical basis and technical guidance for the efficient production in maize drought Breeding.The main conclusions are as follows:1.The actual drought resistance of varieties(express to drought index)followed from strong to weak are:Jingdan 28＞Zhongdan 808＞Zhengdan 958＞Jingke 308＞Liaodan 565＞Jingke25＞Jidan 261＞Nongda 108＞Sidan 19＞Danyu 39＞Shen 21＞Jingdan 508＞DH3719.Uses the method of ciuster analysis and membership function to identify and evaluate frought resistance of varieties.By drought level from weak to strong they are divided into non-resistant varieties—DH3719,Jingdan 508 and Shenyu 21;Resistance varieties—Danyu39,Sidan 19 and Jidan 261;Medium resistant varieties Nongdal08,Jingke308,Jingke25,and Liaodan565:Highly resistant varieties—Jingdan28,Zhengdan958 and Zhongdan808.2.The degree and reasons of maize yields decreasing resulted from water stress vary in different stages.The results we study under water stress at different stages show that any growth stages under water stress may cause maize yields decreasing,and the yields decrease severely at tasselling silking stage,followed by the jointing stage,seedling stage seems relatively lighter.Tasselling silking is the critical period for maize moisture,drought can cause the interval which is from loose powder to silking(ASI)prolonging,result in infertility flowering,kernel number decreasing significantly,thereby seriously affect maize production. Water stress inhibits maize leaves,plant height,root growth and dry matter accumulation,and water stress at jointing stage is the greatest impact to them.3.Use the method of gray relational grade to analysis physiological indicators and drought index.The correlation sizeorder is PSâ…¡photochemical efficiency(Fv/Fm)＞the SOD activity＞ch1a/b＞variable fluorescence(Fv)＞POD activity＞net photosynthetic rate(Pn)＞relative water content＞maximal fluorescence(Fm)＞Soluble protein content＞Proline content＞Soluble sugar content＞Relative conductivity＞Malondialdehyde content＞fixed fluorescence(F_O).The physiological and biochemical indexes and drought resistance of varieties we mentioned above shows a significant correlation,they can be used as good parameters for maize drought resistance identifying indicators,it also can be used for evaluating the drought resistance of corn varieties.4.The accumulation of osmotic adjustment defense drought is one of the physiological mechanisms for maize drought.In the course of water stress,the changes of soluble protein content performance by the trend of firstly increasing and then decreasing and increasing finally,the comparison percentage of soluble sugar content and drought resistance are highly significant negative correlation(r=0.6952^**).Proline content and soluble protein content are increasing,they are in highly significant positive correlation(r=0.7382^**;r=0.6354^**) to the varieties' drought resistance.Maize varieties of strong drought resistance have stronger osmotic adjustment ability than those of weak drought resistance.5.With the time of water stress prolonging,SOD activity and POD activity have increasing trend,they are in highly significantly positive correlation(r=0.9365^**;r=0.8803 ^**)to the drought resistance of varieties.At the same time,MDA content is gradually increasing with the time prolonging of water stress and the comparison percentage of MDA content and drought resistance are negatively correlated(r=0.6909^**),comparing to weak drought-resistance maize,the leaves of strong drought-resistance maize accumulate less MDA,have higher SOD activity and POD activity,it shows that the strong drought-resistance varieties of maize have enzymatic scavenging system which has a strong ability of scavenging radical,and less cell membrane damage.6.Under water stress,chlorophyll content and chlorophyll a/b ratio decrease gradually with the stress time prolonging,water stress not only makes the process of chlorophyll biosynthesis weakened,but also speeds up the chlorophyll decomposition because of the reactive oxygen in plants greatly accumulates.In the process of chlorophyll decomposition, chlorophyll a is probably less stable than chlorophyll b,which results in chlorophyll a/b ratio decreasing,under water stress,chlorophyll a/b ratio and varieties' drought resistance performance highly significant positive correlation(r=0.8869^**).Under water stress, chlorophyll attenuaties so as to avoid the photosynthetic apparatus damage because of excessive absorption of solar energy.7.With the time of water stress,the nitrate reductase activity changes of corn varieties performance a trend of firstly increasing,then dropping,it shows that in the whole stress process,especislly in the early stage of water stress,it can rapidly induct nitrate reductase activity improving,enhance its nitrogen metabolic capacity,in the mid and late stress,nitrate reductase activity continues to decline,and its ability of nitrogen metabolism is inhibited. Water stress makes the leaf net photosynthetic rate of various maize varieties have varying degrees of decline than those for check.The comparison percentage of net photosynthetic rate and the drought resistance of varieties are highly significant positive correlation(r=0.7197 ^**).Water stress makes the carbon and nitrogen metabolism of corn weakening,and inhibits maize growth and development,varieties of strong drought resistance have higher metabolic capacity than the weak ones.8.Water status and photosynthesis in leaves of maize are closely related,with the light response curve of net photosynthetic rate and the CO₂ response fitting we can calculate: Under water stress,the maximum net photosynthetic rate(Pmax),light compensation point (LCP),light saturation point(LSP),the apparent quantum yield(AQY),CO₂ compensation point(CCP),CO₂ saturation point(CSP),apparent CO₂ carboxylation efficiency(β)and dark respiration rate(R_d)of maize leaves are significantly decreas.Maize photosynthetic capacity decreases under water stress.9.Under water stress,basic fluorescence(F_O)increas significantly,the comparison percentage of F_O and drought resistance of varieties shows significantly negative correlation(r =-0.8843^**);Maximal fluorescence(Fm),variable fluorescence(Fv)and PSâ…¡photochemical efficiency(Fv/Fm)decrease,and they are significantly positive correlation(r =0.7944^**;r=0.8987^**)to drought resistance.F_O increases and Fv/Fm declines,it indicates the damage which is not easy to reverse produces a phenomenon of photoinhibition in PSâ…¡reaction center,the primary photochemical activity of PSâ…¡is inhibited,the active center of PSâ…¡is injuried.Varieties of strong drought resistance still have strong photochemical activity,but the degree of their injury is lower.10.Under water stress,photochemical quenching(qP),the actual photochemical efficiency((?)PSâ…¡)and apparent electron transport rate(ETR)decrease,Non-photochemical quenching(qN)increases.qP decline indicates that the proportion of the open parts in PSâ…¡reaction center reduces.Potential activity of PSâ…¡is inhibited.qN increase shows the potential ability of heat dissipation in PSâ…¡,excessive light energy quenches by non-photochemical and many other forms of dissipation,it effectively avoids or reduces the damage to the photosynthetic apparatus which is caused by excessive light absorption of PSâ…¡.Under water stress,ETR and(?)PSâ…¡are lower than the check,you can consider water stress results in the yield of PSâ…¡photochemical quantum declining.The proportion used for photochemical reaction declines,and the photosynthetic electron transport rate decreases.