Rootstock breeding strategies for the mediterranean citrus industry; the somatic hybridization potential

Sour orange was the dominant rootstock used in the mediterranean basin, however, because of the spread of citrus tristeza virus (CTV), there is an urgency to develop alternative rootstocks resistant to tristeza and well adapted to the constraints of the area. Constraints for rootstocks prevailing in the mediterranean context. The major problems affecting this citrus area are salinity, alkaline pH due to calcareous soils, tristeza, nematodes and Phytophthora. A new generation of rootstocks exhibiting good grafting compatibilities with local cultivars of citrus, and cumulating tolerance to these constraints must be worked out. Possible strategies for new rootstock development. Interesting traits of tolerance for biotic and abiotic stresses are present in the Citrus and Citrus-relative gene pools. To use this genetic diversity, the sexual recombination presents some limits because of the citrus reproductive biology and the high degree of heterozygosity of most citrus cultivars and rootstocks; on the other hand, the somatic hybridization is more promising for obtaining good agronomical traits and tolerances to pathogens such as tristeza and Phytophthora. Somatic hybridization program for citrus rootstock breeding. A total of 17 callus lines with potential interest for rootstock breeding was obtained by the Cirad-Flhor team from ovule and seed culture. They were used to isolate protoplasts after electrofusion and somatic hybrids were selected after plantlet regeneration, of which a vigorous and resistant to tristeza promising intergeneric somatic hybrid between P. trifoliata and C. deliciosa, presently propagated by soft-wood cutting for further multilocal evaluations. However, the use of the embryogenic callus obtained after fusion during the regeneration process would be an interesting alternative for mass propagation