The Genetic Origin Of Sour Orange And Sweet Orange And A Preliminary Study On The Change Of Sugar And Acid In Citrus

Citrus is featured in poly-embryo and broad sexual compatibilities.These characteristics resulted in abundant variation and complex phylogenetic relationships.Therefore,the progress of the origin of citrus is slow.Exploration and elucidation of these possible mechanism could lay a foundation for the genetic improvement of citrus.Sour orange and sweet orange,as important species in citrus,played a key role in the research object.Firstly,we investigated the genetic origin of both sour orange and sweet orange using SSR markers.We also obtained a similar hybrids to sweet orange by embryo rescue,hybrid identification,molecular marker screening.Secondly,the conventional quality of different citrus varieties was evaluated.The results of this study are as follows:1.To study the genetic origin of sour and sweet orange,a set of citrus germplasms including mandarin,pummelo,sour orange and sweet orange were analyzed with 206 pairs of polymorphic nSSR primers.The result indicated that sour orange was a possible result between a pummelo(C.grandis)female parent and a wild-mandarin(C.reticulata)male parent,and the similar ratio is 0.79 or more.Sweet orange was a possible result between sour orange and ponkan,with the former as the female parent and later as the male parent and the similar ratio is 0.89 or more.Meanwhile,based on previous research progress,the origin of the sour orange: pummelo × mandarin.The possible origin of the sweet orange:(pummelo ×mandarin A)× mandarin B.2.We further selected 9 citrus varieties from sour orange,sweet orange and their relatives to analyse genetic relationship with 153 pairs of SSR polymorphism primers.The result showed two types of sour orange,named Tujuhong-1(C.aurantium)and Daidai sour orange(C.aurantium),respectively.They are similar to the Jian pummelo-2(C.grandis)which acted as female parent.and the similarity ratio is 0.85 and 0.80,respectively.They are similar to the daoxian wild mandarin-2(C.reticulata)which acted as male parent,and the similarity ratio is 0.89 and 0.85,respectively.The result showed that sweet orange originated from the hybridization with Tujuhong-1(C.aurantium)as the female parent and Jiangan(C.reticulata)as the male parent,and the similarity ratio is 0.90 and 0.93,respectively.3.Four cross combinations using three places of sour orange from Hubei,Guangdong and Sichuan Province as the female parent,Ponkan(C.reticulata)as the male parent,were carried out with 68 fruits.As a result,892 plants were recovered from seeds cultured in vitro.By SSR marker analysis,a total of 215 hybrids were verified.The result of 19 pairs of InDel markers showed that 6 plants from 215 hybrids were similar with sweet orange.By the whole genome resequencing,the GD-137 plant had the similar genetic information with sweet orange on chromosome 2.4.The fruit quality was investigated in 68 citrus.The soluble sugar,titratable acid and AsA contents of Citrus,Fortunella and Atalantia buxifolia were different.In mandarin and orange,the titratable acid content in wild mandarin was significantly higher than that of cultivated mandarin.The high titratable acid content in sweet oranges was more than 1%,while the low acid of the sweet oranges were generally below 1%.Sugar and acid contents were investigated in 56 citrus species.Fructose and sucrose were the main sugar component in C.grandis,C.reticulata,C.aurantium and C.sinensis.However,fructose and glucose were the main sugar component in C.medica,C.limon and C.ichangensis.Meanwhile,citric acid was the main component of the total acid.Total acid and total sugar showed a very significant negative correlation in 56 citrus species.There was a significant negative correlation among citric acid and fructose,sucrose and total sugar in citrus species.