Nuclear Genome Analysis Of Citrus Somatic Hybrids And Their Progeny

Citrus is one of the most important fruit crops in the world. Protoplast fusion technique circumvents the difficulties of citrus genetic improvement by conventional methods, such as polyembryony, different flowering time, pollen/ovule sterility, long juvenility, and creates many unprecedented germplasms. The newly created germplasms enriched the gene bank of citrus. Theoretically somatic hybrids integrate bilateral genetic information and exhibit characteristics of both parents. Whereas variance will occur within the hybrids. The genetic research on somatic hybrids can highlight the principle of hybridization of parents and also contribute -to the practical breeding of fruit crops. In this study, the genetic stability of intergenric and interspecific somatic hybrids in citrus were evaluated by SSR and AFLP analysis. The main results were as follows:i) The statistic showed AFLP analysis can produce average 45 bands with a primer pair. AFLP analysis of the somatic hybrids between Bonnaza navel orange and grapefruit , Newhall navel orange and Bingtang tangerine, showed that some plants lost parents' markers and some possessed new bands absent in the parents. The results show that the fusion processes is accompanied with genetic recombination leading to the loss of some special band or occurrence of some new bands in the hybrids.ii) Similarity coefficency among the fusion regenerates of the 2 intergeneric hybridizations, 'Page' tangelo+ trifoliate orange and Dancy tangerine+ trifoliate orange were much higher. That shows the hybrids seldom varied. In particular, no varience was identifid in the hybrids of Dancy tangerine and trifoliate orange . But much more variation was observed in the interspecific hybrids of Newhall navel orange+ Bingtang tangerine and Bonnaza navel orange + grapefruit. It may be due to the high homogeneity between the parents, which results in high genetic recombination and new bands in AFLP analysis as well. And this result was also confirmed in SSR analysis. SSR analysis demonstrated all the hybrids of interspecific somatic hybrids from Newhall navel orange+ Bingtang tangerine lost the band present in both parents, whereas new band was detected in the SSR fingerprinting of all the hybrids from Cleopatra mandarin + sour orange. But the exact reason for this phenomenon is not certain.iii) AFLP and SSR analysis revealed that the progenies of the hybrids from Key lime+ Valencia orange and Cleopatra Mandarin + Sour orange are very stable at the genetic level and almost no variation was identified.The feasibility of identifying citrus somatic hybrids with SSR analysis was also evaluated in the paper. SSR analysis is applicable for quick screening of citrus somatic hybrids for its advantages, such as time saving, positive demonstration and good repetition. But the shortage of SSR primer limits its application in other plants except several model plants. With the development of bio-informaition, more SSR primers can be attained from GENE BANK and used into some economic and poorly-studied crops.