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Genetic Assessment of Egyptian Citrus Rootstock

Paper type: Assessment
Pages: 6 (1364 words)
Categories: Egypt
Downloads: 7
Views: 2

Characterization of the citrus germplasm in Egypt is critical to the helpful application of modern citrus development approaches to this commodity. In the last decade, several new species of citrus imported from China without any genetic history or phylogenetic and conservation. This study was performed for identification of a few unique Egyptian citrus species (Acidic), was not tested anywhere else before, along with to investigate the comparative phylogenetic relationship with several important Chinese citrus species. Towards this effort, the ubiquitous presence of retro-transposons and microsatellites in plant genomes propose that the implementation of these techniques in combination would permit breeders to achieve unique molecular markers and are effective in the taxonomy and phylogeny of the genus Citrus.

It is well known that, citrus taxonomy and phylogeny are often the topics of controversy and the main problem in citrus breeding, because of their long history of cultivation, the high diversity of phenotypic variation and weak information of the genealogy of complicated admixture in reproduction system and cultivated citrus (Wu et al.

, 2018). In view of the performance of our results, the separation of the three true C. reticulata, C. grandis (C. maxima) and C. medica in distinct clades or subclades in our REMAP and SSR analyses support their distinctiveness as the ” true” or “biological” basal species of edible citrus. This concept has achieved much approval and support through previous molecular studies (Uzun & Yesiloglu, 2012; Amar et al., 2014; Shimizu et al., 2016 and Curk et al., 2016).

Several earlier workers hypothesized C. limon to be of complicated hybrid origin involving two parents: citron and lime (Swingle 1943; Malik et al., 1974 and Scora, 1975), or citron and sour orange (Nicolosi et al., 2000), or sour orange and lime (Torres et al., 1978). The recent report of cytoplasmic and nuclear data of Curk et al., (2016), point to C. medica was very possibly the directly male parent of the main lemon and lime, this due to the shared genomic structure but never to act as an immediate female parent due to the cleistogamy of citron genotypes. In our results, C. limon (Eureka lemon) classified with C. medica (Fingered citron) and C. jambhiri (Rough lemon), this confirms their possible interspecific origin, as already suggested by several molecular sequence studies (Amar et al., 2014 and Wu et al., 2018).

Volkamer lemon is one of the most promising rootstocks in the Egyptian acidic, due to their tolerance to many biotic and abiotic stress. Apparently, it is a more controversial origin (Curk et al., 2016). Earlier authors considered that the ancestors of Volkamer lemon are thought to be the sour orange and lemon (Nicolosi et al., 2000). A possible originated from mandarin x sour orange (Barrett & Rhodes 1976), or mandarin x citron origin was also suggested (Carvalho et al., 2005). Evidence suggested C. medica was the male parent of”Volkamer”lemon,”Mexican” lime, “Rangpur” lime,”Rough” lemon, and”Palestine”lime (Ollitrault et al. 2003 and Curk et al., 2016). Based on our PCA data, we propose that Volkamer lemon is classed with the Egyptian C. limon and C. aurantifolia as the taxon with which it appears to be most closely affiliated. Indeed, our results agree with the last hypothesis, and both nuclear and cytoplasmic data indicate quite distant between volkamer” lemon, citron, “rough” lemon and “rangpur” lime (Snoussi et al. 2012; Penjor et al. 2013 and Curk et al. 2016).

Similarly, it is worth noting that sour orange (C. aurantium) was the main standard rootstock for citrus germplasm (Scora, 1975 and Barrett & Rhodes, 1976) and thought an offspring of C. grandis, C. reticulata and C. medica (Shimizu et al., 2016). In this study, the bitter orange and daidai which are all considered to be sour orange (C. aurantium), all clustered together with lightly aligned with grapefruit and pummelo. This results in agreement with SSR, indel markers and the recent genomic data, support the hypothesis that sour oranges are natural hybrids of a mandarin and a pummel (Barkley et al., 2006; Shimizu et al., 2016 and Wu et al., 2018). Another striking characteristic, the PCA-LTR data provides convincing evidence in supporting that pummelo appeared as the female parent of sour orange, and acidic being the paternal parent. This view was supported by the hypothesis that sour orange showed the contribution of bitter orange and acidic, like the results by Barkley et al., (2006) and Bayer et al., (2009).

Our data assume a close genetic relationship between C. reticulata (mandarin) and C. sinensis (sweet orange) highlight that C. reticulata was sharing between sweet orange and mandarins. Concordant with the view of Barrett & Rhodes, (1976). Several earlier report supports this opinion as C. reticulata was evolutionarily close with C. sinensis and suggested that sweet orange and citron as maybe female and male parents, respectively (Nicolosi et al., 2000). Parallel results were also found in the recent reclassi?cation of citrus origin (Wu et al., 2018), confirming that among mandarins and sweet orange, they find abroad association of relatedness that explains the domestication of these groups.

The grapefruit (C. paradisi) was advised as a natural hybrid between pummelo and sweet orange (Gmitter et al., 2012). Grapefruit has more similarity with pummelo than sweet orange in phenotyping and chemical formation, which indicates a backcross to pummelo. Our data was evolutionarily close grapefruit with pummelo with a small apportion of sweet orange, supporting the view of a hybrid between pummelo and sweet orange, possibly over back introgression to pummelo. Our data confirm this hypothesis since the grapefruit genotypes show identity with all pummelo species, concordant with the recent nuclear genome sequence (Shimizu et al., 2016), supporting the perspective that origins of grapefruit (a pummelo – sweet orange hybrid).

C. grandis, usually known as pummelo, is considered to be a real Citrus species (Scora, 1975 and Barrett & Rhodes, 1976), which provided rise to grapefruits and sour oranges via hybridization. According to the interpretation of the recent genomic data (Wu et al., 2018), the initial pummelo introgression within the mandarin gene pool, then the influence of which was reduced by repeated backcrosses with mandarins. Later, further pummelo introgressions did rise to sweet orange and mandarins. Indeed, the pummelo genome (C.grandis) has been a part of the parentage of several citrus cultivar”s (Barkley et al., 2006). This outcome proves that pummelo was the maternal parent of C. lemon, C. aurantium, C. sinensis and C. paradisi. Our findings agreed with the previously reported of the phylogenetic relationship of pummelo (Tanaka, 1977; Nicolosi et al., 2000 and Penjor et al., 2013) and the chemotypes diversity (Dugrand-Judek et al., 2015), highly supported that grapefruits and sour oranges are direct descendants of pummelos.

The genus Fortunella includes the kumquats, it strongly resembles Citrus species, even though their phenotype is very diverse. Pang et al., (2003), thinking that fortunella was the most initial genus while citrus was in the top phase of evolution. In our results, it is worth notice that Fortunella was nested within the citrus clade. Within this framework, our results synergistically suggest that Fortunella has interspecific variations, but it is a separate exclusive group as a genus, which is in concurrence with earlier reports (Penjor et al., 2013; Amar et al., 2014 and Wu et al., 2018).


Microsatellite and retrotransposons represent a major component of the structural evolution, varying greatly in copy number within the plant genome. To facilitate such purposes, here we report a detailed overview of the discriminating capacity, efficiency and ability of SSR and REMAP markers system in the genus Citrus and related species. A dominant marker REMAP was more sensitive and could discriminate at low taxonomic levels, especially for Egyptian acidic, while a co-dominant SSR marker can differentiate within the group level of citrus.

The PCA and the HCA have drawn a successful annotations relationship in Citreneae species, support the monophyletic nature and provide unambiguous identification or overlapping clusters of real species and related hybrids like lime, lemon, citron, sour orange, grapefruit, mandarin, sweet orange, pummelo and fortunella, resulted in their placement in different clades. This article maybe will provide new information for advancing breeding techniques and developing better conservation strategies in the genus Citrus and its relative species with particular emphasis on the Egyptian citrus rootstock.

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Genetic Assessment of Egyptian Citrus Rootstock. (2019, Dec 20). Retrieved from https://studymoose.com/genetic-assessment-of-egyptian-citrus-rootstock-essay

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