**7. Conclusion**

226 Genetic Diversity in Plants

using ISSR markers. In that study, grapefruits and pummelos were seperated clearly and similarity value of this two species was 0.79. Besides, all pummelos were distinguished and it might be of thier zygotic origin. Same results obtained from SRAP data (Uzun et al., 2011c). At the same way, Yong et al., (2006) also seperated pummelos using SSR markers. It was concluded that pummelos were monoembryonic and there was a high level of

In the grapefruit group some accessions such as 'Wheeny', '*Citrus hassaku'*, 'Cocktail' and 'Oroblanco' were clearly separated from pummelos and grapefruits and nested between this two species according to various marker systems (Uzun et al., 2010; Uzun et al., 2011c). 'Wheeny' originated as a chance seedling in Australia and under heat-deficient climatic conditions in Australia and New Zealand it is a summer-maturing variety. While the fruit is grapefruit-like in most respects, the monoembryonic nature of seeds and some ofthe other characters suggest that it is probably a pummelo hybrid (Hodgson 1967). *C. hassaku* was reported as an independent species (*Citrus hassaku* Hort. Ex Tanaka) and originated as a chance seedling in Japan and its characteristics strongly suggest the pummelo-mandarin parentage with pummelo predominant (Hodgson 1967). On the other hand, *C. hassaku* was notified as a pummelo hybrid (Kahn et al., 2001). 'Cocktail' was indicated as a hybrid between 'Frua' mandarin and low acidity pummelo (Kahn et al.,*.*  2001). Another accession 'Oroblanco' was reported as a hybrid between acidless pummelo

High level of similarity was found in grapefruit cultivars in various studies. Low level of polymorphism was detected in grapefruits and some of them were identical (Uzun et al., 2010; Uzun et al., 2011c). Fang and Roose (1997) found very low polymorphism in grapefruits based on ISSR data and notified that all grapefruits were derived from the same ancestral tree by mutation. There was no variation in grapefruits in other previous studies based on izozyme (Roose, 1988) and SSR (Luro et al., 2000) data. At the same way, Corazza-Nunes et al. (2002) detected high level of similarity in grapefruits. Most grapefruits, despite considerable variation in agronomical traits such as, rind and flesh color, fruit size, were nearly identical (Fig. 7). Cultivars with distinct morphological characters (pigmented or yellow flesh colour, seedy and seedless fruits) such as

Henderson, Ruby, Duncan showed complete genetic similarity (Uzun et al., 2010).

Fig. 7. Although grapefruits have distinct fruit characters, low level of genetic variation

found among them (from left to right; Davis Seedless, Shambar, Red Blush).

polymorphism in the pummelos (Yong et al., 2006).

and grapefruit (Kahn et al.*,* 2001).

It is reported preservation of the genetic diversity represented in all the plant ecosystems throughout the world has become a major issue of international concern. The loss of increasingly large numbers of plant species through habitat destruction threatens the availability of a diverse plant germplasm base which will be needed to feed future generations. *Ex-situ* conservation of genetic resources of citrus was considered as imperative for this situation. (Bretting and Widrlechner, 1995, as cited in The Citrus and Date Crop Germplasm Committee, USA, CDCGC, 2004). Approaches to *ex-situ* conservation include methods like seed storage, field genebanks and botanical gardens. DNA and pollen storage also contribute indirectly to *ex-situ* conservation of genetic resorces. Advances in biotechnology, especially in the area of *in vitro* culture techniques and molecular biology provide some important tools for improved conservation and management of plant genetic resources (Rao, 2004).

It is suggested better understanding of genetic diversity and its distribution is essential for its conservation and use. It will help us in determining what to conserve as well as where to conserve, and will improve our understanding of the taxonomy and origin and evolution of plant species of interest. Information of these subjects is essential for collecting and use of any plant species and its wild relatives. Understanding genetic diversity that is present in collections is required to better management of conserved germplasm. Through improved characterization and development of core collections based on genetic diversity information, it will be possible to exploit the available resources in more valuable ways (Rao & Hodgkin, 2002).

Genetic variability in citrus is considered to be the result of many factors, such as hybridization, mutation and type of reproduction (mostly apomictic). The low intraspecific diversity found in cultivated species such as sweet orange contrasts with the high variability of agriculturally important traits such as ripening period and color and size of fruits (Herrero et al., 1996, as cited in Novelli et al., 2006). Understanding of genetic diversity in Citrus is essential for planning and application of breeding programs, establishing germplasm collection and carrying out molecular studies. It is also important for citrus researcher and breeders to arrange their future studies.

### **8. Acknowledgements**

The authors wish to thank Kahraman GURCAN from Agricultural Biotechnology Department of Erciyes University for his valuable assistance.
