Drought Resistance Evaluation And Physiological Mechanism Of Brassica Napus Germplasm

In recent years,drought has occurred frequently.As one of the three rape types with the best comprehensive characters,Brassica napus has relatively poor drought resistance and high requirements for water.Therefore,it is very important to screen the germplasm materials of Brassica napus with strong drought resistance and improve the drought resistance evaluation system at different growth stages.In this study,six core germplasm of Brassica napus were used as materials.PEG simulated drought method was used in germination stage and pot water control method was used in budding stage to analyze the morphological and physiological characteristics of Brassica napus under different treatments.Based on the drought resistance coefficient,the drought resistance ability of each material was identified by comprehensive evaluation methods such as principal component analysis,membership function analysis and grey correlation analysis.Screening drought resistance identification indexes at different growth stages to provide theoretical basis for drought resistance germplasm evaluation and drought resistance breeding of Brassica napus.The test results are as follows:1.After PEG treatment,the changes of germination characteristics of 6 Brassica napus materials were analyzed.It was found that the germination rate,seedling rate and seedling height decreased significantly,the germination and seedling time were delayed,and the growth rate slowed down.Among them,the germination rate was more than 90% and grow stably on the 2th day after 0%-15% PEG treatment,but the growth is still less than 85%on the 7th day after 25% PEG treatment.The seedling rate and seedling height changed significantly among materials with the extension of treatment time;The main root length elongated continuously under the treatment of 0%-10% PEG,then began to decline,and the root length injury rate could reach 63.21%,and the higher the PEG concentration,the slower the increase in 7 days;The biomass per plant also increased first and then decreased,but lagged behind the length of taproot,and the maximum value was concentrated in 15%-20%.2.After analyzing the changes of agronomic characters after drought stress at the bud stage,it was found that the change trend of agronomic characters of the six materials was basically consistent with that at the germination stage.The above ground fresh weight,stem diameter and heel diameter decreased with the aggravation of drought.Among them,the above ground fresh weight was greatly affected by drought(35.52%),reached a significant level among all treatments,and the variation range of stem diameter and heel diameter was relatively small;The biomass gathered to the main stem and root,resulting in the increase of stem dry weight and root dry weight,and the decrease of leaf dry weight.When the drought is serious,some rape materials are seriously inhibited,the overall biomass accumulation decreases,and the decrease of stem weight is greater than that of root weight,so the root shoot ratio increases significantly.3.The analysis of the changes of physiological indexes of rape in different growth stages under drought stress showed that the water content in the two growth stages decreased significantly with the aggravation of drought.The water content in the germination stage decreased sharply when the PEG concentration was 20%,which was 59.07% lower than that of CK.However,a large amount of water was lost in the bud stage under MD treatment,which was worse than that in the germination stage.The changes of MDA content in different periods were basically the same,but the change range was small at the bud stage,and the degree of membrane lipid peroxidation was light.In addition,the change range of MDA content was negatively correlated with the drought resistance of rape materials.After drought treatment,the activities of antioxidant enzymes and osmoregulation substances increased first and then decreased,and there was little difference between the two periods.The chlorophyll content also increased first and then decreased,but the chlorophyll content in the bud stage was higher than that in the germination stage,and the photosynthetic capacity was strong.4.The comprehensive analysis of germination characteristics and physiological index changes during germination showed that the changes of each index were representative when PEG concentration was 10% and 20%,which could be used as a reference concentration for PEG simulation of drought stress test.5.The drought resistance of six materials in two growth stages was comprehensively evaluated by principal component analysis and membership function analysis.The evaluation results of drought resistance in germination stage were XY3 > XY2 > XY5 >XY6 > XY1 > XY4,and the drought resistance in bud stage was XY2 > XY5 > XY6 >XY3 > XY1 > XY4.XY2 and XY5 showed high drought resistance in both periods,which can be used as the core parents for breeding drought resistant varieties.The grey correlation analysis showed that Pro,CAT,germination rate,SP,water content,Chla were highly correlated with drought resistance during germination of Brassica napus,while SS,Chla/b,taproot length,POD,stem diameter and SOD were highly correlated with drought resistance at budding stage,which could be used as reference indexes to measure drought resistance identification at each stage.The correlation degree of MDA in the two growth stages is the smallest,so it should not be used as a reference index.