Genetic Identification Of 'Luzhai' Sweet Orange And A Graft Chimera Of Citrus

Spontaneous mutation often occurs in Citrus orchards,Some bud mutation and chimera can be directly used for breeding.Here we analyzed the quality of two field bud sports and identified their genetic background and differences to related cultivars by morphological observation and molecular marker,such as SSR(Simple sequence repeat),AFLP(Amplified fragment length polymorphism) and SSAP(Sequence-specific amplification polymorphism).The results indicated both were new germplasms and could be applied to the industry as elite cultivars.'Luzhai' sweet orange(Citrus sinensis),a bud mutant of sweet orange found in Guangxi,has stable genetic traits;a putative chimera of navel orange(Citrus sinensis)/Satsuma mandarin(Citrus unshiu),found in top-worked navel orange orchard(using Poncitrus trifoliate as the rootstock and Satsuma mandarin as inter rootstock),has fruits with appearance resembling 'Washington' navel orange and the pulp color similar to Satsuma mandarin.Main results are as followed:1.The flavor of 'Luzhai' sweet orange mature fruit is of rich flavor.The content of TSS is about 15%,however,that of TA is lower than 0.5%.Besides the higher content of fructose,sucrose,and glucose than those of 'Bingtang' sweet orange at 63.03 mg/g,43.49 mg/g and 72.17 mg/g respectively,the content of quinic acid,malic acid and citric acid are also much higher than those of 'Bingtang' sweet orange.There oxists significant difference in the phylliform index,the stoma density and stomatal longitudinal diameter between 'Luzhai' sweet orange and 'Bingtang' sweet orange,but was not in the transverse diameter.In morphology,the phylliform of 'Luzhai' sweet orange is almost elliptical, with higher stoma density and different stoma size,the anther and megaspore are normally developed as well.SSAP analysis indicated that polymorphism locus existed between 'Luzhai' and 'Bingtang' sweet orange.2.A graft chimera was discovered which originated from the top work of 'Washington' navel orange(Citrus sinensis) scion onto Satsuma mandarin(Citrus unshiu). The graft chimeras and their donors were investigated in morphology,cytology, biochemistry as well as by molecular markers.Some characters of the chimera,such as juice sacs,stoma length,which were determined by L1 cell layer,were similar to those of Satsuma mandarin,while other characteristics determined by L2 cell layer resembled 'Washington',including pollen morphology and fertility and seeds number.The extract from the fruit pulp of chimera and their donors was studied using HPLC.The results indicated that the mature fruit of the chimera had the same carotenoids profile as Satsuma mandarin,in whichβ-cryptoxanthin accumulated predominantly in the juice sacs.SSR and cpSSR analysis suggested that both nuclear and chloroplast genomes of the chimera were composed of its donor plants respectively.Based on the results above,we concluded that the chimera was a periclinal chimera consisting of L1 derived from Satsuma mandarin and L2/L3 from 'Washington' navel orange.It combined the valuable traits of its donor plants and could be used as a commercial cultivar for the fresh market of citrus industry.