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Variation of plants derived from indirect somatic embryogenesis in cotyledon explants of papaya

Siwaporn Homhuan^a, Boonyuen Kijwijan^a, Preeya Wangsomnuk^a, Kitti Bodhipadma^b, David W.M. Leung^c,*

 
ABSTRACT:     Somatic embryogenesis in papaya (Carica papaya) cv. Kaekdum was induced from embryogenic callus derived from cotyledon explants by culturing on modified half-strength MS basal medium supplemented with 15 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D), 400 mg/l glutamine, 80 mg/l adenine sulphate, 170 mg/l NaH₂PO₄·H₂O, 15% (w/v) coconut water, and 60 g/l (w/v) sucrose. The somatic embryos were grown on modified half-strength MS basal medium supplemented with 2 mg/l 2,4-D and 60 g/l sucrose. Upon transferring to MS basal medium, somatic embryo germination and plantlet conversion were observed. Variations at the morphological and molecular level were examined in the somatic embryo-derived plants which, after acclimatization, were grown under field conditions. Three types of primers (S-02, S-03, and S-07) were used for random amplified polymorphic DNA analysis. The results from DNA fingerprints revealed both monomorphic and polymorphic bands with sizes ranging from approximately 190–7120, 120–4990, and 280–3600 base pairs, respectively. The size differences might be related to morphological variations observed in the field-grown papaya plants derived from somatic embryogenesis. These morphological variations include plant height, number of flowers, floral length, number of fruits, fruit dimension, and fruit shape. Since these plants produced only hermaphrodite flowers, it is likely that the somaclonal variation could occur in field-grown papaya plants derived from indirect somatic embryogenesis.

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* Corresponding author, E-mail: david.leung@canterbury.ac.nz

Received 11 Feb 2008, Accepted 10 Sep 2008