Studies On The Photosynthetic Characteristics And High Temperature Resistance Of Different Raspberry Cultivars

Raspberry（Rubus idaeus）is a popular fruit for the third generations in the world,for its fragrance,pleasant tastes and reasonable nutrition composition,which also has a strong effect on health care.It has extensive market and good prospects for development.Many cities are actively engaged in the introduction and cultivation.Anhui province has a mild and sunny climate,four distinctive seasons.But in summer,temperatures in this area often approach 35⁴0℃,sometimes even higher.High temperature has become the most significant abiotic stresses which limiting the growth and productivity of raspberry in this area.At present,there are few reports on the high temperature resistance of raspberry varieties.In order to explore the photosynthetic characteristics and heat resistance of different raspberry varieties,and provide scientific basis for the correct selection of cultivars in production.The main research object of this experiment is three red raspberry varieties（‘Autumn-Bliss’,‘Heritage’,and‘U.S.Ruby’）.In the determination of changes in photosy-nthetic parameters,supplemented with blackberry（‘Hull’）,wild raspberry（‘Rubus xantho-carpus Franch’）for comparative analysis.During the treatment of high temperature stress,physiological and biochemical indicators of the three red raspberry varieties were analyzed,compare the heat resistance of different raspberry varieties by the principal component analysis.The results of the study are as follows:1.The diurnal variation of photosynthetic parameters of the five raspberry cultivars showed a“double-peak”pattern.The peaks appeared at 9:00 and 15:00,and there were obvious“midday breaks in photosynthetic characteristics”,which were mainly the combined effects of stomatal limitation factors and non-stomatal limitation factors.As a result,the stomatal limitation factors dominated;the changes in the intercellular CO₂concentration（Ci）and stomatal limitation（Ls）were in the opposite direction,and the increase in stomatal limitation was closely related to the midday depression of raspberry.2.The net photosynthetic rate（Pn）of five raspberry varieties was as follows:Rubus xanthocarpus Franch>Hull>Autumn-Bliss>Heritage>U.S.Ruby;The transpiration rate（Tr）,stomatal conductance（Gs）and the light use efficiency（LUE）of blackberry and wild raspberry were higher than three red raspberry varieties,while the WUE was the opposite;photosynthesis was more affected by the ecological factors,and Tr and Gs were dominant factor in the photosynthetic rate of raspberry.3.The light saturation point（LSP）of three red raspberry varieties ranged from 839 to898μmol·m^-2·s^-1,and the light compensation point（LCP）ranged from 17 to 24μmol·m^-2·s^-1.The apparent quantum efficiency（AQY）at 0.028-0.044,the CO2 saturation point（CSP）is between 1475-1500μmol·mol^-1,the CO₂ compensation point（CCP）is between 60-90μmol·mol^-1,and the carboxylation efficiency（CE）is between 0.039-0.057mol·m^-2·s^-1;Autumn-Bliss has the highest LSP and CSP,Heritage has the highest LCP,CE,and the lowest CCP,U.S.Ruby has the highest AQY,and LSP is the smallest;They are all shade C₃ plants.4.During the high temperature stress process,the relative electrical conductivity, malondialdehyde（MDA）content,and proline content of three red raspberry varieties all increased with the increase of temperature,the increase in electrical conductivity and MDA content of Heritage and U.S.Ruby were greater,and the increase in Autumn-Bliss’s Pro content was greater;The contents of SOD and soluble protein increased at first and then decreased.Autumn-Bliss increased the most,and U.S.Ruby decreased the most.Chlorophyll content showed a downward trend.The higher the temperature,the greater the decline.The fall of Autumn-Bliss was lower than Heritage and U.S.Ruby.5.The principal component analysis method was used to evaluate the heat tolerance of three red raspberry cultivars.According to the scores and contribution rates of the 6 factors,Autumn-Bliss 0.782>Heritage 18 0.309>U.S.Ruby-0.241.Autumn-Bliss has strong heat resistance.Heritage and U.S.Ruby have poor heat resistance.