Plant regeneration of Carica papaya L. through somatic embryogenesis in response to light quality, gelling agent and phloridzin

Difficulties to develop an easy and reproducible protocol to get healthy and well formed plants from somatic embryos of papaya (Carica papaya L.) had included low germination, callus production at the base of the embryo radicle and the occurrence of hyperhydric plantlets among others, and by consequence unsuccessful transfer to the field. With the aim of improving a propagation method, the effects of light quality, gelling agent and phloridzin concentration on the germination of somatic embryos of hermaphrodite C. papaya L. var. Maradol were studied. Somatic embryos were grown on half strength MS medium, with the addition of Chen vitamins [Chen, M.H., Wang, P.J., Maeda, E., 1987. Somatic embryogenesis and plant regeneration in Carica papaya L. tissue culture derived from root explants. Plant Cell Rep. 6,348-351], solidified with three distinct gelling agents: Sigma (R) Agar-Agar, Difco (R) Bacto agar and Phytagel (R); supplemented with phloridzin and exposed to different light qualities: blue (54 mu mol m(-2) s(-1)), red (65 mu mol m(-2) s(-1)), gro-lux (68 mu mol m(-2) s(-1)), red + blue, white (32 mu mol m(-2) s(-1)) and wide spectrum (49 mu mol m(-2) s(-1)) during a period of 4 weeks. Results show that light quality and gelling agent had important effects on germination and plant growth, while 3.0 mg L-1 phloridzin had an important role on germination as well as in root development. Somatic embryos exposed to white light, culture medium solidified with 3.0 mg L-1 phytagel and 3.0 mg L-1 phloridzin showed longer roots. Meanwhile, germination and plant length were promoted on an improved culture medium solidified with 7.5 g L-1 Difco (R) Bacto agar, 3.0 mg L-1 phloridzin and exposed to gro-lux lamps. Under these conditions, 70% of somatic embryos germinated and developed normal roots without hyperhydricity. The regenerated plantlets with well developed roots and shoots were successfully transferred to a greenhouse with a survival rate of 95%. (C) 2008 Elsevier B.V. All rights reserved.