ORIGINAL ARTICLE

Evaluation of Drought Stress Factors Response on Somatic Embryogenesis and Plantlet Regeneration from Mature Caryopsis Culture in Traditional Indian Black Rice (Oryza sativa L.)

The present study was aimed to establish the induction of embryogenic callus followed by plantlet regeneration under the drought stress conditions induced by Polyethylene glycol (PEG) and Mannitol in Indian Black rice (Oryza sativa L, Co 57), a traditional Indian cereal food. Mature caryopsis was used as an explant for the induction of embryogenic callus cultured on Murashige and Skoog (1962) medium fortified with 2,4-dichlorophenoxyacetic acid (2.0mg/L) either alone or in combination with various concentrations of mannitol (25mM, 50mM, 100mM, 150mM, and 200mM) and also on medium enriched with various concentrations of PEG (0.5%, 1.0%, 2.5%, 5.0%, and 7.0%) in order to achieve the drought tolerant embryogenic callus. Moreover, plantlet regeneration could be possible from the sub-culture of embryogenic callus to MS-medium fortified with 2.0mg/L of 6-benzylaminopurine (BAP) in combination with 0.5mg/L of α- Naphthalene acetic acid (NAA) in presence of mannitol (25mM, 50mM, 100mM, and 150mM) and also on PEG (0.5%, 1.0%, 2.5%, and 5.0%) supplemented regeneration medium. Results revealed that mannitol concentration was increased up to (200 mM) in presence of 2, 4-D (2.0mg/L) was proved to be lethal for the induction of somatic embryogenesis followed by plantlet regeneration. However, mature caryopsis explants cultured on high concentration of mannitol (150mM) fortified nutrient medium produces the low frequency (33.23±1.84^a %) of somatic embryogenesis and also the minimum number (4.98 ± 0.28^a) of somatic embryos per callus. Similarly, the high concentration of PEG (5.0 %) produces the low frequency (21.66±1.61^a %) of somatic embryogenesis and minimum number (4.04 ±0.57^a) of somatic embryos per callus. Significantly, the high concentration (150mM) of mannitol with BAP (2.0mg/L) and NAA (0.5mg/L) was observed to produce the low frequency of drought tolerant plantlet regeneration (10±0.57^a %) and minimum number (1.80±0.21^a) of plantlets per embryogenic callus whereas during PEG treatments, the lowest frequency (8.12 ±0.58^a %) of plantlet regeneration and the minimum number (1.61 ±0.19^a) of plantlet regeneration could be recorded. Furthermore, drought tolerant plantlets were transferred to plastic cup soil and gradually acclimatized under the greenhouse conditions. Present study thus establishes regeneration technique under drought conditions in black rice crops that could be useful for the improvement in rice crop in general and black rice in particular.