Application Of Single Nucleotide Polymorphisms In Citrus Hybirds Identification

Citrus plants are mostly polyembronic, and their breeding progenies are therefore mostly nucellar seedlings, which makes it very difficult to obtain sexual seedlings. It is necessary to make early identification of the hybrids in order to increase breeding efficiency and reduce cost.DNA molecular markers are useful in the identification of sexual seedlings. In this study, we tried to use Single Nucleotide Polymorphism (SNP) markers to identify nucellar and sexual seedlings. Two methods, Single Strand Conformation Polymorphism (SSCP) of the PCR products and Allele Specific PCR (AS-PCR), were exploited to identify specific SNPs.Five crosses were made in this study. They were:w.murcott×418 tangerine, w.murcott×Xingyi dahongpao, jiangjin sweet orange×Xingyi dahongpao, Shatangju×Xingyi dahongpao, Xingyi dahongpao×Shatangju. Seeds from mature fruits were sowed to grow seedlings to use as experiment materials.Nine carotene biosynthesis genes were cloned from 418 tangerine and w.murcott. CHX (β-carotene hydroxylase) gene was found to possess numerous SNPs which are potential sites for PCR investigations.Although the CHX genes from 418 tangerine and w.murcott bare different SNPs, however, those SNPs were found to be difficult to be used in designing PCR primers for allele specific PCR while PCR-SSCP could only idengtify some of the hybrids. From our analysis, it should be possible to identify hybrids of w.murcott×Xingyi dahongpao, jiangjin sweet orange×Xingyi dahongpao, Shatangju×Xingyi dahongpao, Xingyi dahongpao×Shatangju using allele-specific PCR. We are going to try the method once the seedlings are big enough.