Influence of surfactants on growth and regeneration from mature internodal stem segments of sweet orange (Citrus sinensis) cv. Hamlin

The development of a reliable shoot regeneration system for mature tissue of citrus is of major importance to accelerate the evaluation of commercial traits. Three non-ionic surfactants were evaluated independently in terms of their affects on the growth and regeneration of mature internodal stem segments of sweet orange cv. Hamlin in culture. Growth and shoot development of explants were influenced by type of surfactant added to the regeneration medium DBA3, its concentration and order of flush growth used for explant preparation. Supplementation of Pluronic F-68 at 0.001% (w/v) to the medium was the superior treatment resulting in significantly higher fresh weight gain of explant, improved mean number of shoots per explant and the percentage of explants giving shoots (33.5% from first flush) and shoot yield was twofold higher compared to treatments without surfactant (17%). Triton X-100 was the least responsive in terms of its affect on the growth and regeneration of stem segments but such shoots had a normal phenotype. Explants cultured on DBA3 medium containing Tween 20 exhibited growth and shoot yield similar to treatments without surfactant, but at concentrations 0.01-0.5% (v/v), the shoots became vitrified and failed to graft successfully in vivo. Growth and shoot yield of explants showed a general decline between flushes especially from second and third harvests. Shoots derived from stem segments which were cultured on media containing Pluronic F-68 and no surfactant had a higher survival rate (70-80%, respectively) compared to treatments using Triton X-100 at 0.001-0.1% (v/v) (33% survival). All acclimatized grafts exhibited typical mature wood characteristics and flowered 14-16 months after transfer to the greenhouse.