| Wheat is one of the important grain crops in China and an important food source for human beings,and its yield and quality are directly related to people’s living standards and national food security.Growth and development under natural conditions can be greatly influenced by environmental factors,and abiotic stresses in the environment have a particularly pronounced effect on the growth and development of the crop.The wheat germination period is also an important period to measure the strength of drought resistance of wheat.Plants are subjected to environmental stresses such as drought during growth,which affects the yield of wheat.Therefore,exploring drought resistance identification methods for wheat,screening drought-resistant germplasm resources of wheat,and revealing the physiological mechanisms of drought resistance in wheat can provide theoretical guidance for research to enhance the level of drought resistance in wheat and lay the foundation for further cultivation of new drought-resistant germplasm.In this study,337 representative wheat materials were selected and treated with PEG-6000 to simulate drought conditions,and the differences of five traits,including germination potential,germination rate,plant dry mass,aboveground dry weight and belowground dry weight,were investigated under drought stress.The drought tolerance indexes were selected and evaluated by using a combination of drought tolerance coefficient(DC),frequency distribution analysis,drought tolerance evaluation value(D value),principal component analysis,affiliation function analysis,cluster analysis and stepwise regression analysis.At the same time,wheat varieties with different drought resistance were selected as test materials,and different concentrations of PEG-6000 were used to simulate different degrees of drought stress,and the differences of four wheat varieties with different drought resistance levels were initially revealed by measuring physiological index parameters.The main results were as follows.1.337 wheat varieties were tested for drought stress during the germination period using-0.5 Mpa of PEG-6000 to simulate drought stress.The results showed that the germination potential,germination rate,plant dry mass,aboveground dry weight and belowground dry weight of each variety were reduced to different degrees;the results of paired t-test showed that they all reached a highly significant level(P < 0.01),with t-values ranging from-83.992 to-26.236,indicating that all indicators were inhibited and reduced under drought stress,but the degree of inhibition of each indicator by drought stress varied differed.The correlation and frequency analysis of each index showed that the correlation coefficient between each index was significantly positive,and the correlation coefficient between relative germination potential and relative above-ground dry weight was 0.551,while the correlation coefficient between relative plant dry mass and relative below-ground dry weight was 0.997.The different distribution frequencies of each index easily caused the information of each index to cross each other,and there were large deviations in the identification of drought resistance of varieties,which could not obtain objective and accurate evaluation results.Therefore,it is necessary to introduce comprehensive indicators to evaluate the drought resistance of wheat.2.The drought resistance coefficients of each index were transformed into three new independent composite indexes through principal component analysis,and the composite index values of each principal component were calculated and combined with the affiliation function method to find out the comprehensive evaluation value(D value)of drought resistance of 337 wheat varieties,the higher the D value,the stronger the drought resistance.Cluster analysis was performed using Rstudio software,and the results screened 29 highly drought-resistant varieties,88 drought-resistant varieties,107 drought-sensitive varieties,and 113 drought-hypersensitive varieties.Correlation analysis was conducted between the comprehensive evaluation value of drought resistance(D value)and the drought resistance coefficient of germination index,and the drought resistance coefficient of each index was highly significantly and positively correlated with the D value,indicating that the D value was reliable and effective as a criterion for drought resistance identification.The correlation coefficients of germination potential and germination rate with D value were the highest,0.846 and 0.926,respectively.stepwise regression analysis showed that the indicators closely related to D value were germination potential and germination rate,therefore,germination potential and germination rate could be used as preliminary screening indicators for wheat drought resistance identification.3.Four different types of drought-resistant materials were randomly selected by the previous D value ranking results and the classification results of cluster analysis: the highly drought-resistant material Nanda 2419,the drought-resistant material Tianmai 989,the drought-sensitive material 14MA-429,and the highly drought-sensitive material Zhoumai38.The chlorophyll content,antioxidant enzyme activity,MDA content and free proline content of the four materials were measured at 10% PEG-6000(mild drought)and 20%PEG-6000(severe drought),and it was found that with the increase of drought stress,the total chlorophyll content of each material maintained the trend of increasing and then decreasing,and the POD and SOD activities increased,and the increase was consistent with the drought tolerance category.The increase in POD and SOD activities was consistent with the drought resistance category,with Nanda 2419 > Tianmai 989 > 14MA-429 > Zhoumai 38,CAT activity showed a trend of increasing and then decreasing,and MDA and free proline content both showed an increasing trend.Compared with the control,MDA content increased by 14.40% and 48.74% under mild drought and severe drought in Nanda 2419;36.89% and 60.81% in Tianmai 989;44.47% and 78.73% in 14MA-429;and 77.65% and113.56% in Zhoumai 38.Zhoumai 38 showed the greatest differences under different drought stresses,while Nanda 2419 showed the least difference and showed the strongest resistance.The free proline content of Nanda 2419,Tianmai 989,14MA-429 and Zhoumai38 increased by 47.69%,40.49%,29.09% and 10.53% under mild drought,and 3.04 times,2.69 times,2.56 times and 2.54 times more than the control under severe drought. |
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