Abstract:
Higher production of Sri Lankan Citrus spp. is needed to reduce the import expenditure. Lack of elite planting material
is one of the major barriers for intensive cultivation. Development of an efficient in vitro regeneration protocol is
essential for elite planting material production and genetic improvement of Citrus. This study evaluated the effect of
maltose concentration on local Citrus spp. for direct somatic embryogenesis followed by plant regeneration. Mature
embryos of Naran (Citrus crenatifolia), Heennaran(Citrus reticulate) and Panidodam (Citrus sinensis) were used as
explants. In experiment 1, cotyledons of Naran were placed in 100mg/l and 200mg/l of maltose with liquid MS to
select the effective maltose level. Multiple som atic embryos formed from single Naran cotyledons after 5 days of
culture. Significantly higher frequency of som atic embryogenesis was observed from 200mg/l maltose level. In
experiment 2, Heennaranand panidodam cotyledons were placed in selected level of 200 mg/1 of maltose. Somatic
embryos of Heennaran cotyledons developed into seedlings of different heights from 0.5 cm to 5 cm after 5 days of
cotyledon culture. Percentage of first somatic embryogenesis from total explants was 87% . The secondary somatic
embryos were formed in 30°/fr of cotyledons. In Panidodam, 78% and 69% of initial and secondary somatic embryos
were formed, respectively. A significant difference could not be detected between two species on somatic
embryogenesis on 200 mg/1 of maltose level in liquid MS culture. Possibility for genetic transformation of Citrus was
also tested: Cotyledon explants were transformed by Agrobacterium bearing 35S: VlmybA2 for induction of
anthocyanin pigments. Putative 35S: VlmybA2somatic embryos emerging from transformed cotyledons, produced
purple dots after 1 week of culture indicating the potential of transformation. This study indicates the potential of this
protocol for efficient somatic embryogenesis for future multiplication and crop improvement programmesthrough
genetic transformation of Sri Lankan Citrus spp.
