The same treatment for transgenic shoot regeneration elicits the opposite effect in mature explants from two closely related sweet orange (Citrus sinensis (L.) Osb.) genotypes

Abstract

In citrus, production of mature transgenic plants belonging to different genotypes is an important biotechnological objective. In the present study, we tried to genetically transform and regenerate mature plants from the economically important Navelina sweet orange cultivar by using the procedure previously established for the genetically close Pineapple sweet orange variety. The use of BAP at 3 mg l−1 promoted efficient shoot organogenesis in Pineapple as expected, but not in Navelina. Furthermore, different effects were observed when the auxin α-naphtalene acetic acid (NAA) was added to BAP-containing regeneration media. Although NAA addition at 0.5 mg l−1 enhanced cambial callus formation, number of shoots and their elongation in Navelina, the contrary effect was observed in Pineapple. Moreover, transformation efficiency in Navelina rose from 0 to 3% but declined from 6 to 0% in Pineapple, indicating that BAP and BAP + NAA exerted the opposite effect in transgenic shoot regeneration from two closely related cultivars. This suggests that small changes in the procedure could induce drastic alterations in regeneration and even increase the likelihood of obtaining transformants from non-responsive genotypes. Moreover, the vigour of the starting plant material and the addition of kanamycin as selective agent were determining for the generation of mature sweet orange transgenic plants.