| Rape is the main oil crop in Tibetan areas,and as the main source of cooking oil,the study of rape is particularly important for Tibetan areas.Low temperature is the main limiting factor for the growth of rapeseed at high altitude.Unreasonable planting density leads to poor light exposure of individual plants.It remains to be discussed whether low light conditions affect the low temperature tolerance of rapeseed.In this study,54 hybrid progeny of brassica juncea and brassica napuscreated by our research group were used as experimental materials.Different light intensities were set,and the differences of morphological indexes,physiological and biochemical indexes of rapeseed under different light intensities were compared.At the same time,the low temperature tolerance of rapeseed under different light intensity was compared and the low temperature tolerance of rapeseed under low light and high light were selected.The results showed that:(1)The hypocotyl length was inversely proportional to light intensity,and leaf area,root length and other morphological indexes were proportional to light intensity.(2)Based on the low light resistance coefficient and membership function formula,through the calculation of morphological and physiological indicators;Three cultivars with strong tolerance to low light and four cultivars with no low tolerance and high sensitivity to low light were screened.It was found that chlorophyll content,photochemical efficiency(ETR)and photochemical quenching(qp)values of rapeseed growing under high light were significantly higher than those growing under low light.(3)Through the analysis of chlorophyll fluorescence parameters and chlorophyll of rapeseed growing under different light intensity,it was found that low temperature would significantly reduce the values of ETR,qp and chlorophyll of rapeseed.(4)In order to further verify the influence of low temperature on chlorophyll fluorescence parameters and other indexes of rapeseed,by comparing the influence of low temperature on the total content of Fv/Fm,qp,NPQ,ETR,chlorophyll a,chlorophyll b,carotenoid and chlorophyll under different light intensity,experimental measurement indexes of rapeseed growing under high light were decreased respectively after low temperature treatment:15.56%,79.88%,80.29%,80.52%,16.8%,17.72%,18.433%,20.62%;The indexes of rapeseed growing under low light were decreased by5.16%,26.1%,103.2%,25.75%,23.48%,23.37%,25.66% and 24.32%,respectively.(5)Based on the formula of low temperature tolerance coefficient and low temperature tolerance membership function,one strong low temperature tolerance strain,eight low temperature tolerance strains,seven no low temperature intolerance strains,and three no low temperature intolerance and high sensitivity to low temperature were screened through calculation and comparison of no low temperature tolerance coefficient and membership function under low light.Based on the formula of low temperature tolerance coefficient and low temperature tolerance membership function,by comparing the low temperature tolerance coefficient and membership function under high light,2 strong low temperature tolerance lines,7 low temperature tolerance lines,4 no low temperature intolerance lines,3 no low temperature intolerance and high sensitivity to low temperature were screened.It was also found that the chlorophyll fluorescence parameters of the strong-tolerance strains screened under different light intensity were less affected by low temperature than those of the no low-tolerance strains.(6)Cross analysis of low temperature resistant strains and low temperature resistant strains screened under different light intensity;It was found that strain XZ2 showed good low temperature tolerance under different light intensities,and strain XZ20,XZ41 and XZ42 showed low temperature tolerance under different light intensities.(7)Through the correlation analysis of chlorophyll fluorescence parameters of rapeseed before and after low temperature stress under different light intensity,it was found that with the decrease of temperature,the synthesis of chlorophyll would be affected,As the main carrier of plant photosynthesis,chlorophyll has an important influence on the physiology and biochemistry of rapeseed as for The net photosynthetic rate(photochemical efficiency ETR)and light energy utilization rate(photochemical quenching qp)were decreased.In this study,phenotypic and physiological indexes of the hybrid progeny of brassica juncea and brassica napus were analyzed under different light intensity and low temperature conditions.The low light tolerance strains and low temperature tolerance strains under different light intensity were screened and obtained,which provided theoretical support and germplasm basis for the cold resistance gene mining and breeding of the hybrid progeny of hybrid progeny of brassica juncea and brassica napus. |
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