Evaluation And Physiological Mechanism Of Drought Resistance In Rape Seedling Stage

Drought is one of the most common threats to environment and the most serious limiting factor in crop production.Rapeseed is one of the important oil crops in our country.The drought resistances of different varieties can be widely different.This experiment will use PEG6000 to stimulate an arid environment.The effects of drought on the growth of rapeseed in seedling stage will be systematically studied by comparing 504 genotypes and filtering 10 genotypes that have different resistances.The main conclusions are as follows:(1)Drought stress can reduce shoot fresh weight,dry weight,root dry weight,and leaf water content to varying degrees.But reductions of different genotypes are not the same.The responses of different genotypes' s root morphology such as primary root length,total root length,root surfarea,root volume,root avgdiam and root tips to drought stress are different.Drought stress can increase the root-shoot ratio of genotypes with different resistance.(2)The comprehensive evaluation of the drought resistance of 504 rapeseed genotypes and the related analysis of different indexes of the rapeseed genotypes show that the correlation coefficient r between drought resistance subordinate value U and shoot fresh weight,dry weight,root dry weight,total dry weight,total root length,of root volume is all greater than 0.7,and the correlation coefficient with root dry weight,root surfarea and root volume is greater than 0.8.The results show that the root surfarea and the volume of root system in root morphology represent a stronger drought resistance in seedling stage,which could be used as the screening index of drought resistance genotypes.(3)By taking the value U as the dependent variable and drought resistance coefficient of each trait index as the independent variable,the experiment makes a regression analysis of 504 rapeseed genotypes.The results show that the variation interpretation rate of the root system,such as root dry weight,root surfarea and root volume,to drought-resistance membership function is higher than 70%,while the rate of shoot fresh weight and dry weight,total dry weight,total root length is only about 50%.(4)Among rapeseed genotypes of the same growth,varieties with strong resistance have more developed roots.Under drought conditions,the root morphology of drought-resistant genotypes,such as root length,total root length,root surfarea,root volume,root tips,is not significantly increased or decreased,but the root morphology of sensitive genotypes is significantly decreased.(5)In this experiment,a drought-resistant membership function value method based on drought resistance coefficient was used to comprehensively evaluate 504 genotypes.33 strong resistant rapeseed genotypes and 13 sensitive rapeseed genotypes were selected.Comprehensive analysis of various morphological indices of different resistant genotypes showed that the aboveground part of sensitive genotypes is larger but that of drought-resistant genotypes is smaller under normal condition.The primary root length,total root length,root surfarea,root volume and root tips of the sensitive genotypes are decreased,while the root avgdiam of root system was increased.But the primary root length,total root length,root surfarea,root volume and root tips of drought-resistant genotypes were elevated,while the root avgdiam of root system decreased.(6)Through the specific analysis of the drought resistance coefficient of different resistance rapeseed genotypes,drought stress can improve the root-shoot ratio of different resistant genotypes,and the biggest correlation between sensitive genotypes and membership function values is root tips,and the root tips is positively correlated with total root length and root surfarea.The most significant correlation between drought-resistant genotypes and membership function values is the root surfarea.(7)The results of water culture test on drought resistance of different resistant rapeseed materials showed that the accumulation of proline,soluble protein and the content of MDA in Leaf were lower than that of sensitive material(408)in resistance material(61).(8)The potted test of the drought resistance of different rapeseed materials showed that drought stress can significantly reduce the photosynthesis of rape seedlings,under the same drought stress,the net photosynthetic rate,stomatal conductance and transpiration rate of stronger drought resistant materials(61,404)are larger than those with weaker drought resistance(141,408).