INFLUENCE OF PHYSIOLOGICAL STATE OF FRESH AND DRY EXPLANTS ON IN VITRO CULTURE RESPONSE IN RICE (Oryza sativa L.)

Fresh or dry naked seed-explants of different maturity were cultured in vitro and their responses were investigated on a medium containing 2mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) as growth regulator. It was found that the explants at lower maturity had lower rates of callus induction and lower production of callus masses than those with the more matured ones in the original cultures. However, the quality of the callus induced from the younger explants was much better since the ratio of somatic embryogenic to non somatic embryogenic callus produced by younger explants was higher and grew faster in the subsequent proliferation cultures. In comparison with fresh young seed-explants and dry ones at the same maturity, dry ones generally responded better in terms of the rate of callus induction and the quality of callus. The strategy of using immature naked seed-explants for obtaining more embryogenic callus was highly effective especially for those varieties with relatively poor in vitro culture response.