Somatic hybridization for citrus rootstock breeding: an effective tool to solve some important issues of the Mediterranean citrus industry

Abstract

The prevalence of sour orange rootstock in the southern and eastern part of the Mediterranean Basin is presently threatened by the spread of Citrus Tristeza Virus (CTV) and its main vector Toxoptera citricida, combined with abiotic constraints such as drought, salinity and alkalinity. The search for alternative CTV-resistant rootstocks that also withstand the other constraints is now considered an urgent priority for a sustainable citrus industry in the area. Complementary progenitors can be found in citrus germplasm to combine the desired traits, particularly between Poncirus and Citrus genera. The production of somatic hybrids allows cumulating all dominant traits irrespective of their heterozygosity level, and would appear to be an effective way to solve the rootstock challenge facing the Mediterranean citrus industry. This paper presents the results obtained during a regional collaborative effort between five countries, to develop new rootstocks by somatic hybridization. New embryogenic callus lines to be used for somatic hybridization have been created. Protoplast fusions have been performed at CIRAD and IVIA laboratories, focusing on intergeneric combinations. Analysis of ploidy level by flow cytometry and molecular markers confirmed the acquisition of new interesting tetraploid somatic hybrids for six combinations. Diploid cybrids with intergeneric (Citrus × Poncirus) nucleus and C. reticulata or C. aurantifolia mitochondria were also identified for four combinations. The agronomical performance of a pre-existing somatic hybrid between Poncirus trifoliata and Citrus reticulata was validated in calcareous soils in Morocco. Somatic hybridization is now integrated into the breeding programs of the five Mediterranean countries.

Population dynamics of aphids (Aphididae) on orange (Citrus sinensis ‘Thomson Navel’) and mandarin (Citrus reticulata ‘Blanco’)

“…The citrus industry is one of the main components of Mediterranean agriculture, helping to guarantee incomes in underprivileged rural zones. Furthermore, citrus fruits provide the main source of vitamin C in the Mediterranean Basin, contributing to the general nutritional supply (Dambier et al, 2011). In Algeria, the citriculture has a strategic importance because it is a source to supply fresh fruits (Biche, 2012).…”

Protoplast fusion in the genus Gentiana: genomic composition and genetic stability of somatic hybrids between Gentiana kurroo Royle and G. cruciata L.

“…These markers include the most popular, namely, RAPD (Xu et al 1993;De Filippis et al 1996;Szczerbakowa et al 2003;Guan et al 2010), microsatellites SSRs (Fu et al 2003;Cappelle et al 2007;Dambier et al 2011), AFLP (Brewer et al 1999;Guo et al 2002;Fu et al 2004;Tu et al 2008), ISSR (Scarano et al 2002;Trabelsi et al 2005;Xiao et al 2009) and, more recently, DArT markers (Smyda-Dajmund et al 2016). …”

Progress in plant protoplast research

“…Somatic hybridizations and cybridizations in Citrus resulted in rootstocks resistant to biotic and abiotic constraints and in increased yield and fruit quality (Dambier et al 2011), as well as in brown spot resistant scions (Soriano et al 2012). New seedless triploid Citrus cultivars are produced via haploid + diploid fusion and symmetric fusions of elite diploid cultivars can lead to superior allotetraploid breeding parents (Grosser and Gmitter 2005).…”