SNP Polymorphisms Among Individual Wild Citron Plants (Citrus Medica) Growing In Ruili, Yunnan And Development Of SNP Markers For Citrus Maxima

Citrus have been cultivated for more than 4,000 years. They are also notorious for being able to hybridize between different species from even different genera, and for being easy to produce bud mutations. All these have added to our difficulty of doing classification and cultivar identification researches.DNA molecular markers have provided new means for the studies of citrus taxonomy and cultivar identification, and single nucleotide polymorphism (SNP) markers are especially useful for their high occurrence in the genome. Analysis of SNPs should allow us to better evaluate the genetic diversities of citrus plants and better understand the phylogenetic relationships among species and genera. SNP markers can also be used in the construction of genetic maps, in the analysis of gene functions, and in the marker-assisted breeding etc.In this study, SNP markers were used to analyze the genetic diversities of the wild citron (Citrus medica) plants growing in Ruili, Yunnan province and pommelos (Citrus maxima) in the national citrus germplasm repository of China. Results are as follows:A. Studies on the genetic diversities of wild citrons growing in Ruili, YunnanLeaves of 15 individual citron plants were collected from 3 local populations(â… ,â…¡,â…¢) growing wild in Ruili, Yunnan province. PCR-SSCP was used to screen for SNP markers and a total of 15 polymorphic SNP primers were identified from 102 primer-pairs. Polymorphic electrophoresis bands were scored and clustered. The results showed that these individuals could be clustered into 3 groups by SNP polymorphisms. Plantâ…¡5 stood out as a single group.â…¡1,â…¡2,â…¡6 andâ…¢1,â…¢2,â…¢5,â…¢6 were grouped together as a second group. The rest samples were clustered as a third group. It was shown that there is no relevance between molecular markers' results and geographical distribution, indicating that there was no clearly identifiable genetic drift or all these individuals belonged to the same breeding population. It was shown that combined use of SNP markers identified all citron samples used in this study, demonstrating that SNPs are capable of discriminating individual citrus plants.B. Studies on the genetic diversities of pommelo cultivarsPrimers suitable for analyzing SNPs in pommelos were screened by using PCR-SSCP technique. In the mean time, allele-specific primers were designed to investigate the potential of using allele-specific or hyplotype-specific PCR to evaluate the genetic diversities among pommelo cultivars. Results indicated that hyplotype-specific PCR could efficiently identify 59 tested pommelo samples and should be a valuable method for the identification of pommelo cultivarsC. ConclusionsPCR-SSCP was capable of showing the SNP polymorphisms and discriminating individuals of wild Citrons with relatively high efficiency.Allele-specific PCR had higher efficiency and less time-consuming in the identification of SNPs than PCR-SSCP and should be more useful in the future.