The Research On The Tolerance Of Citrus Rootstock Ziyangxiangcheng (Citrus Junos Sieb.) To Alkaline Stress And Its Effects On Scion Growth And Fruit Quality

Citrus is widely cultivated in China,the acreage of the citrus industry in our country rank the first in the world,but some citrus producing areas are facing soil abiotic stress because of the significant differences in natural conditions and diverse soil types.Especially,in the saline and alkali environment,the photosynthetic rate of citrus plants decreased,the growth was slow and finally reduced the yield and fruit quality.Citrus is a grafted cultivated crop,rootstocks are very important for the growth and development of plants.Therefore,it is of great significance to studying the tolerance of citrus rootstocks to salt and its effects on fruit quality for improving the citrus industry status.In this study,‘Lunwan' navel orange grafted on Citrus junos(Cj)and Poncirus trifoliate(Pt)rootstocks,the content differences between Cj and Pt were analyzed which include the mineral elements,hormones,lignin,glutathione,vitamin E and citric acid.Analyzed the fruit sugar metabolic differences from physiological and molecular levels.The main findings are as follows:1.The content of mineral elements,as well as hormones,lignin,glutathione,citric acid and vitamin E in different parts of ‘Lunwan' navel orange grafted on Cj and Pt rootstocks were measured.The absorption and transport efficiency of mineral elements in Cj were higher than that in Pt in the saline environment.The content of K in roots,perennial branches and new leaves in Cj were much higher than that in Pt;and the content of Na in roots,perennial branches in Cj were also significantly higher than that in Pt;however,the content of Na in annual branches were converse.Leaves are the most sensitive part to deficiency of mineral elements,the content of Fe,Mn,Zn,Cu in new leaves were significantly higher in Cj than in Pt,and the content of Zn,Cu in old leaves were also much higher in Cj than in Pt.The content of IAA in Cj roots were significantly higher than that in Pt,but ABA content in roots and leaves were much lower in Cj than in Pt.In roots,the citric acid content in Cj were significantly higher than that in Pt,but the content of malic acid were opposite.GSH is a free radical scavenger,the content of GSH and VE in roots were much higher in Cj than in Pt,but there were no significant difference in leaves.The content of lignin in roots and leaves were significantly higher in Pt than in Cj.2.The fruit of ‘Lunwan' navel orange grafted on Cj and Pt were both harvested at 140,210,240,270 and 300 days after flowering(DAF).The physiological qualities in Cj and Pt ‘Lunwan' navel orange during fruit ripening were measured.The single fruit weight and peel thickness were higher in Cj than in Pt during fruit ripening;the content of VC were significantly higher in Pt than in Cj in the harvest ripening stage;Pt has finished coloring but Cj is starting to turn color at 210 DAF.There were some differences in the content of soluble sugar and organic acid in fruit between two kinds of rootstocks.The content of sucrose,glucose and fructose were much higher in Pt than in Cj at 240 DAF and 270DAF;however the content of citric acid were converse;and there were no significant differences in soluble sugar and organic acid contents between the two kinds of rootstocks fruits in the last ripening stages.According to the comparing analysis of transcript levels of sugar and orignic acid related genes,we found that the transcriptional peak of CsSS,CsSPS,CsSUC4,CsHXK1,CsPKP3,CsCS4,CsACO1,and CsGS1,which are involved in the synthesis and transport of sucrose,the synthesis and degradation of orignic acid were earlier in Pt than in Cj during fruit ripening.The expressions of CsSS,CsSPS,CsSUC1,CsSUC4,CsGDH1,CsGS1 were increased rapidly at 300 DAF.