The Effect of Plant Growth Regulators (PGRs) on Efficient Regeneration of 12 Recalcitrant Indica Rice (Oryza Sativa L.) Genotypes

Biotechnological approaches provide an efficient and expeditious system for developing agronomic features of rice at the cellular and molecular level compared to traditional breeding methods. The in-vitro regeneration method optimization of recalcitrant indica rice genotypes is a critical step for the biotechnological approaches for further development as the optimum concentrations of Plant Growth Regulators (PGRs) for in-vitro regeneration vary from genotype to genotype. Here, 12 important rice genotypes, including local cultivars and varieties, were collected from different regions of Bangladesh and evaluated for their in-vitro regeneration potentiality. Mature dehusked sterilized rice seeds were inoculated on different basal media (MS, N6, B5) supplemented with different concentrations of 2,4-Dichlorophenoxyaceitic acid (2,4-D) for callus induction. Induced calli were transferred to N6 media supplemented with different combinations of 6-Benzylaminopurine (BA) and 1-Napthaleneacetic Acid (NAA) for shoot induction. Regenerated shoots were rooted on half-strength MS media without supplementation of any hormones. Treatments of different concentrations and combinations of plant growth regulators showed varying results. Maximum callus induction frequencies were observed with 2.5-3.0 mg/l supplementation of 2,4-D on N6 media where Saat, Jamaibabu and Nimikhanai showed the highest callus induction frequencies (84.44%; 78.89 and 80% respectively) and maximum shoot initiation was observed at 2.5 mg/l BA +1.0 mg/l NAA and 3.0 mg/l 6-BA +1.5 mg/l NAA supplemented media where rice genotypes BRRI Dhan71, Nayapaijam, Nimikhanai and BRRI Dhan28 showed the highest shoot induction frequencies-86.67, 85.00, 86.67 and 88.33% respectively. Nearly all of the induced shoots showed root formation on half-strength MS media. This study demonstrates variations in regeneration response of the rice genotypes where cultivars Jamaibabu, Nayapaijam and Nimikhanai showed the highest in-vitro regeneration potential.