| Drought has become an important environmental stress that affect the world agricultural production.Canola(Brassica napus)is one of the most important oil crops in China,drought often occurs in spring and autumn.Researches concerning on the growth and development of canola response to drought stress and physiological metabolic mechanism could reveal the mechanism of drought resistance,which would be of great importance for improving drought tolerance and breeding drought tolerant cultivars.In this experiment,nine canola genotypes were used to conduct water stress,thereafter canola cultivars with drought tolerance were screened out and used to compare drought tolerance among different growth stages and analyze physiological mechanism responsing to drought stress occurred at different growth stages.The main results are as follows:(1)Two drought tolerant and two drought susceptible rapeseed genotypes were screened out through drought tolerance evaluation.According to change of MDA,proline content,stomatal conductance and other physiological index and yield of nine canola conventional genotypes under drought condition at flowering and by using combination of drought-resistant coefficient method and principal component analysis,drought resistance genotypes Zhongshuang No.5(G7),Alku(G8)and drought sensitive genotypes NORIN 40(G2),LINE 40(G5)have been screened out.(2)Canola yield and quality were greatly influenced by drought stress at flowering stage.The results of four genotypes under drought stress at different stages showed that drought stress at flowering had the greatest influence on yield,followed at pod stage,and there is no significance at seedling stage.Drought stress at flowering leaded to yield decreased in a range of 20.0%?49.2%.Compared the effect of drought stress on yield component at different stages,drought stress at flowering make the pod numbers per plant decreased in a range of 19.4%?58.2%,seed numbers per pod decreased in a range of 15.7%-20.1%,while 1000-seed weight increased in a range of 22.0%?37.4%;the opposite trend was observed at seedling stage and pod stage.The drought stress at flowering and pod stage leaded to the increase of protein content and decrease of oil content in seeds.(3)The largest decline of dry matter accumulation in the drought process was at seedling stage;the largest decline of dry matter accumulation at maturity was at flowering stage.Measuring the dry matter accumulation at the end of drought stress,drought stress at seedling stage had a great influence on it.The dry matter accumulation decreased in a range of 22%?38%,followed by the flowering,and drought stress at pod stage had a smaller influence on dry matter accumulation.When the drought plant were watered,the growth recovery was greatest at seedling stage.At maturity,drought stress of seedling and pod stage had no significant influence on biomass,while biomass decreased in a range of 17%?35%under drought stress at flowering.(4)Drought stress at flowering stage had a greatest influence on plant height and the length of main inflorescence.The rapeseed morphological indexes reduced with no significance under drought stress at flowering and pod stage.Plant height and the length of main inflorescence reduced significantly under drought stress at flowering.The plant height of G2 and G8 decreased by 9%and 8%(P<0.05),respectively.The length of main inflorescence of G2,G5 and G8 decreased by 24%,20%and 19%(P<0.01),respectively.(5)Drought resistance of canola was correlated with intercellular CO2 concentration negatively,and correlated with water use efficiency positively.Drought has caused net photosynthetic rate,stomatal conductance and transpiration rate decreased,and the decreased amplitude was increased as the drought stress stronger,the decrease amplitude was highest when the soil water was 50%?30%.As the drought stress stronger,intercellular CO2 concentration decreased firstly and then increased,the decrease of intercellular CO2 concentration of drought-sensitive genotypes G2 and G5 was higher than that of drought-resistant genotypes G7 and G8,so there was a negative correlation between the decrease amplitude and drought resistance of canola genotypes.As the drought stress stronger,the water use efficiency and stomatal limitation value were increased firstly and then decreased,the stomatal limitation value of drought-sensitive genotypes G2 and G5 are higher than drought-resistant genotypes G7 and G8,the increase amplitude is correlated with drought resistance of canola genotypes negatively.The increase amplitude of water use efficiency of G7 and G8 were higher than G2 and G5,and it was correlated with drought resistance of canola genotypes positively.(6)The increase of conductivity was lower and that of leaf temperature was higher under drought stress.Under drought stress,the proline content,MDA content and electric conductivity of canola leaves were increased with stronger drought stress.The increases were higher at flowering stage;the increase of drought-resistant varieties increased is relatively small.Different growth stages in soil moisture content falls below 30%,the physiological indices began to rise significantly.When Soil moisture down to 20%,The proline content of different varieties in the flowering under drought stress increased to 72?100 times,the MDA content increased to 59?133 times,the conductivity increased 34?579 times;among of them G8 were the lowest value.Leaf temperature of canola was increased under drought stress at seedling and flowering,and the increase amplitude was positively correlated with drought resistance of canola genotypes,and the increase amplitude of leaf temperature of G7 and G8 was higher than that of G2 and G5 at flowering stage.Leaf temperature of canola were decreased slightly under drought stress at pod stage,but the decline was not significant.(7)Drought stress occurred at flowering stage affected canola yield and was the most sensitive stage for identification of drought tolerant cultivars.Flowering stage of canola plants comprised of leaves,flowers and pods and showed the most growth increment,which was also the most sensitive to drought stress.Drought stress occurred at flowering stage reduced the rate of photosynthesis and dry matter accumulation,which also affected flowering and pollination,finally reduced the pod number per plant and seeds per pods,thus resulted in reduced canola yield.While at pod stage of canola,the growth and development was mainly from pod due to leaves abscission,therefore the inhibiton degree of pods number was much lower than that at flowering stage.The thousand seed weight was also affected,while the yield reduction degree was lower than that at flowering stage but higher than that at seedling stage.Drought stress occurred at seedling stage mainly reduced dry matter,but showed nonsignificant effects on seed yield.Therefore,the identification of canola cultivars' drought tolerance should be conducted at flowering stage.By combining agronomy and physiological characters at flowering and pod stages from two growing seasons,Alku(G8)was the most drought tolerant and Zhongshuang No.5(G7)was after;NORIN 40(G2)was the most drought susceptible and LINE 40(G5)was after. |
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