Study On Response Of Different Peanut Cultivars To Drought Stress And Rewatering And Its Mechanisms

Peanut is an important oil crop in our country,the cutltivated area of peanut in China is only next to that of rape,which occupies 1/4 of the cultivated area of oil crops.The total yield is the first of the national oil crops,which accounts for more than 50%.Because of stronger drought and barren resistance,peanut has become the first choice of crops in the arid and semiarid rain-fed region to develop the agricultural production.In China and around the world,peanuts are often grown in sandy loam,or area lack of irrigation,in most of the peanut planting area,rainfall distribution is usually not uniform in growing season,and they often fluctuate between months and years.Compared to other crops,peanut drought resistance is stronger,but on the critical stage of their demand for water,water lack also resulted in severe or irreversible inhibition on peanut growth and development.According to statistics,70% of the peanut cultivated area in our country are threatened by drought,the annual yield loss caused by drought reached 30%~50%.At the meantime,drought also causes decline of quality and greatly increases the risk of peanut to pollution of Aspergillus.Therefore,drought stress is the most important abiotic factor that limits peanut yield and quality improvement.This study we chose five peanut varieties of different drought resistance,study their plant traits,photosynthetic characteristics,osmotic adjustment function,proline metabolism,antioxidant properties,pods and seeds quality changes in respose to drought stress and rewatering at different growth stages.Clear the mechanism of drought resistance for different peanut varieties.It can perform an important function for identification and evaluation of peanut germplasm resources to drought resistance more accurate and effective,mining of different advantage traits of peanut varieties to drought resistance,and strengthen specific of drought breeding and effectiveness of water-saving cultivation.The experiments were conducted at the Field Crop Research Station of Shandong Agricultural University during 2013-2014.The main research results are as follows:1.Biomass(yield)and drought resistance of different peanut cultivarsDrought resistant coefficient is ratio of crop yield affected by drought stress and crop yield of control(unstressed by drought),it is an widely used standard for drought resistance identification and evaluation in current.In our study,drought resistance coefficient method was used to evaluate the drought resistance of the five peanut varieties,the results showed that drought resistance of the five peanut varieties performed consistently in response to drought and rewatering at the seedlings stage and pod setting stage,they ranked in the order: Lipudahuasheng > Shanhua 11 > Huayu 20 > ICG6848 > Hua 17.Identified drought resistance of the five peanut varieties immediately when the drought treatment was over at the seedlings stage and pod setting stage,results showed large difference to this.It suggested that there was compensation effect after the peanut plant experiented drought stress and rewatering.In the peanut production,the occurrence of drought is usually intermittent,and more attention should be paid to the compensation effect after drought.2.Biomass and harvest index response to drought stress and rewatering at the pod setting stageLipudahuasheng gained the highest drought tolerance,because the biomass did not differ significantly,and its harvest index became higher.While percentage of stem for Hua17 got higher,it was a waste of assimilate,and its biomass and harvest index both declined significantly,so yield for it decrease markedly,drought coefficient for it became the lowest.3.Plant traits response to drought stress and rewateringIn the investigated plant traits,was affected the most both at the seedlings stage and pod setting stage drought stress.The number of nodes on main stem of different peanut varieties was relatively stable in different water environment.Green leaf number on main stem was affected larger by drought stress at the pod setting stage,of the four peanut varieties except for Shanhua 11,ratio of green leaves on main stem under drought treatment to control at the pod setting stage increased significantly,indicating that drought stress extended their growth period.Because in peanut production,the growth of the first pair of lateral branches development status directly affects the number of flowers and pods of the whole plant,it can be concluded,change of branch length under drought stress is one aspect of peanut yield change.In terms of varieties,at the seedlings stage,Shanhua 11 and ICG6848 recovered better when rewatering after the drought stress treatment.At the pod setting stage,lateral branch length of Lipudahuasheng recovered closely to control when rewatering after drought stress.While under drought stress both at the seedlings stage and pod setting stage,branch length of Hua 17 was inhibited the smallest in all the five peanut varieties,after rewatering,the compensation effects was the lowest and the growth recovery degree was minimum.4.Photosynthetic characteristics response to drought stress and rewateringDrought stress at the seedlings stage did not cause irreversible inhibition to peanut photosynthetic characteristics.Under pre-flowering drought stress,photosynthetic characteristics and main chlorophyll a fluorescence parameters of the five experimental peanut varieties decreased,while most of them showed slightly over compensation effect after rewatering.SPAD value was stable in different water environments at the seedlings stage.It suggested that drought stress at the seedlings stage may not decrease the yield of peanut,suitable drought may promote the increase of yield.Photosynthetic organs and photosynthetic metabolism were sensitive to moisture at the pod setting stage,leaf SPAD value of the five peanut varieties increased under moderate drought stress,decreased after rewatering.Specially,photosynthetic characteristics and main fluorescence parameters of ICG6848 and Hua 17 declined under drought stress,and did not restore completely to control level after rewatering,this is the basic for their lower drought tolerance.5.Osmotic adjustment response to drought stress and rewateringProline,soluble sugar,free amino acid and soluble protein played a role in osmotic adjustment to some degree under drought stress.Among the four organic osmotic adjusting substances,proline was the most important as its content enhanced significantly higher than the other's.At the seedlings stage,it responded to drought more quickly for the drought resistant peanut varieties Lipudahuasheng and Shanhua 11 and medium drought resistance peanut variety Huayu 20.Moreover,the four organic osmotic adjusting substances quickly recovered equally to the control level,this is why growth for these cultivars can recovered quickly after rewatering,so it is one important reason for their enhancement of drought tolerance.On the contrary,for drought sensitive cultivars,such as ICG6848 and Hua17,the four organic osmotic adjusting substances did not timely recover to the control level,this is not beneficial for the recovery of their growth and development,so they gaied a relatively low drought coefficient.At the pod setting stage,after rewtering,content of proline in the drought resistant peanut varieties,did non recover to the control level,this is beneficial for relief damage from the other potential environmental threats,this is important for the formation of yield.However,content of soluble sugar in the drought sensitive cultivars remained higher,this is detrimental for the pod development and mature,so they gained lower yield and their drought coefficient lowed.6.Proline metabolism response to drought stress and rewateringIn higher plants,proline is synthesized from glutamate or ornithine.The rate-limiting enzyme of glutamate pathway is P5 C synthetase(P5CS).Proline synthesis through ornithine is catalyzed by ?-ornithine transaminase(OAT).Under drought stress,increased proline also contributes to the inhibition of PDH.Our results showed that proline metabolism differed induced by drought stress in different growth stages.Increase of proline content under drought stress at the seedlings stage was mainly due to the increase activity of P5 CS.Under drought stress at the pod setting stage,differences for proline content depended mainly on the comprehensive harmonies response of OAT and PDH activity.7.Antioxidant properties response to drought stress and rewateringDrought stress induced enhancement of superoxide removal related enzyme such as SOD,POD and CAT activities to different extent for the five peanut varieties.At the seedlings stage,higher POD and CAT activity after rewatering was related to higher peanut drought resistance.At the pod setting stage,higher SOD and CAT activity is good for the recovery of their growth and development,this is beneficial for relief damage from the other potential environmental threats,this is important for the formation of yield,and this is an important reason for peanut getting higher drought tolerance.8.Quality response to drought stress and rewatering at the pod setting stageAfter experiencing drought stress at the pod setting stage,yield of Lipudahuasheng increased was due to the increase of sound pod number and improvement of the total sound pod weight,the reduce of immature pod number and decrease of total immature pod weight.Yield of the other 4 peanut cultivars reduced under drought stress,was mainly due to the decrease of pod and kernel weight.After drought stress in higher crude protein and amino acid content increased in the seed kernel only for Huayu 20,reduced for the rest four varieties.Percentage of three kinds of restrictive amino acid was increased in the seed kernel for Lipudahuasheng and Huayu 20.Oil content for the five varieties of peanut were decreased after drought stress,in addition to Hua 17,the O/L became larger.This indicates that peanut seed kernel quality is not relevant to drought resistance among varieties.