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Analysis of genetic diversity in Tunisian citrus rootstocks

Snoussi Trifa H., Duval M.F., Garcia-Lor A., Perrier X., Jacquemoud-Collet J.P., Navarro L., Ollitrault P.. 2015. In : Navarro Luis (ed.), Sabater-Muñoz Beatriz (ed.), Moreno Pedro (ed.), Peña Leandro (ed.). Proceedings of the XIIth International Citrus Congress: International Society of Citriculture. Leuven : ISHS, p. 147-154. (Acta Horticulturae, 1065). International Citrus Congress: Citrus and Health. 12, 2012-11-18/2012-11-23, Valence (Espagne).

Breeding and selection of new citrus rootstocks are nowadays of the utmost importance in the Mediterranean Basin because the citrus industry faces increasing biotic and abiotic constraints. In Tunisia, citrus contributes significantly to the national economy, and its extension is favored by natural conditions and economic considerations. Sour orange, the most widespread traditional rootstock of the Mediterranean area, is also the main one in Tunisia. In addition to sour orange, other citrus rootstocks well adapted to local environmental conditions are traditionally used and should be important genetic resources for breeding. Prior to initiation of any breeding program, the exploration of Tunisian citrus rootstock diversity was a priority. Two hundred and one local accessions belonging to four facultative apomictic species (Citrus aurantium, sour orange; Citrus sinensis, sweet orange; Citrus limon, lemon; and Citrus aurantifolia, lime) were collected and genotyped using 20 nuclear SSR markers and four InDel mitochondrial markers. Sixteen distinct Multi-locus genotypes (MLGs) were identified and compared to references from French and Spanish collections. The differentiation of the four varietal groups was well-marked. Each group displayed a relatively high allelic diversity, primarily due to very high heterozygosity. The Tunisian citrus rootstock genetic diversity is predominantly due to high heterozygosity and differentiation between the four varietal groups. The phenotypic diversity within the varietal groups has resulted from multiple introductions, somatic mutations and rare sexual recombination events. This diversity study enabled the identification of a core sample of accessions for further physiological and agronomic evaluations. These core accessions will be integrated into citrus rootstock breeding programs for the Mediterranean Basin.

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