Evaluation Of Cold Resistance Of Phlox.L Introduced To Heilongjiang Province And Their Response Mechanism To Low Temperature Stress

Phlox paniculata L.and Phlox subulata L.having the characteristics of cold-resistant,rich color,long flowering period and high ornamental value were widely planted in the world.Accordingly,they have become an important flower species for landscaping in cold areas.However,there is little research on Phlox paniculata and Phlox subulata.Especially,the researches on functional genes related to cold had not been reported.In this study,we selected Phlox paniculata L.and Phlox subulata L.as materials to screen normally wintering varieties.Additionally,we analyzed and evaluated the ornamental characteristics of the materials.Then we discussed the relationship between the physical and chemical indicators by the method of low temperature stress.The stress temperature was 20 °C(CK),10 °C,0 °C,-10 °C,-20 °C.At the same time,transcriptome sequencing was carried out and resistance genes related to cold were excavated.These results provided the foundation for cold resistance mechanism and application of Phlox paniculata and Phlox subulata in cold area.The main results were followed:1.22 Phlox varieties from domestic and foreign lands were introduced and planted in Harbin.As a result,14 Phlox varieties including seven Phlox paniculata varieties and seven Phlox subulata varieties were screened out and they can live through the winter.According to phenotypic characteristics,ornamental evaluation and practical application,Phlox subulata is suitable for application in early spring large-scale mountain,slope,mosaic flower bed for crawl growth,early florescence,strong cold resistance.And Phlox paniculata is suitable for the fall,roads,flowers habitat landscape park for long florescence,large inflorescences and abundant flowers.The collocation of two Phlox varieties can formed three seasons landscape.These results provided the reference data for Phlox L.including landscape application,landscape design,etc.2.Several physiological indexes and Chlorophyll content related to cold resistance were determined under low temperature stress.The results showed that the physiological indexes of overwintering Phlox varieties showed regular changes with temperature drop under different temperature stress.Chlorophyll content,soluble sugar content,soluble protein content,Pro content,MDA content and SOD activity were increased with the decrease of treatment temperature.Chlorophyll content reached the peak at 10 °C.The contents of soluble protein,Procontent,MDA content and SOD activity reached the peak at 0 °C,and the soluble sugar content reached the peak at-10 °C.The peak value was decreased with the decrease of treatment temperature.The physiological indexes of ‘Sub-05' and ‘Sub-Jan-04' having cold-resistant characteristics were significantly higher than those of other low cold-resistant varieties.After the peak,the temperature continues to decline.The decreasing range of physiological indexes was significantly lower than that of other varieties with low cold resistance.These physiological indexes are closely related to cold resistance.The strong cold resistant cultivar‘Sub-05'was used for cold resistant gene research further.3.A strong cold resistant cultivar ‘Sub-05' was treated and then sequenced by transcriptome sequencing.99174 unknown genes sequences were obtained.Compared to CK(20 °C),8302 genes were up-regulated and 9898 genes were down-regulated at 4 °C;10638 genes were up-regulated and 17876 genes were down-regulated at 0 °C;11021 genes were up-regulated and12358 genes were down-regulated under at-10 °C.These genes play an important role in the resistance to low temperature stress.4.Six genes,including antioxidant enzyme genes(PsSOD and PsPOD),transcription factors(PsICE1 and PsCBF/DREB genes),cold regulated genes(PsCOR413pm)and(PsCOR413im)were cloned and the serial number of every gene was also obtained.Gene expression under low temperature stress showed that the expression levels of PsSOD and PsPOD gene and the expression levels of PsCBF/DREB gene were increased with the decrease of temperature.The maximum change was 10 times higher than that of the control group(20 °C).The expression levels of PsCOR413 pm and PsCOR413 im were increased rapidly at 4 °C,but decreased slightly at 0 °C and-10 °C,and still higher than that of control group at 20 °C.The results showed that the cloned target gene had a response relationship with cold stress.Cold resistant genes were cloned.It was further confirmed the accuracy of the above sequencing results.