Differential Role of Indolebutyric Acid in Sugarcane Root Development

Abstract

Auxin biosynthesis, metabolism, transport and signaling pathways are crucial for plant growth and development, including rhizogenesis. Sugarcane shoots regenerated under in vitro conditions develop roots without supplementary addition of exogenous plant growth regulators. However, robust rooting in engineered clones and in vitro multiplied shoots of sugarcane is of interest to biotechnologists for mass propagation and adaptation of plants in the environment. Here we report that Indolebutyric acid (IBA), being precursor of Indoleacetic acid, has differential role in regulating the development of roots. Shoots developed under in vitro conditions of an elite genotype US-127 were placed on rooting medium, containing different levels (0.0, 1.0, 2.0, 3.0, 4.0, 5.0 and 10.0 mg L⁻¹) of IBA. Under in vitro conditions, root length varied from maximum (6.99 ± 0.17 cm) to minimum (0.50 ± 0.07 cm) in plants supplemented with IBA from 0.0 to 10 mg L⁻¹ in the multiplication medium. A dramatic change in root growth was observed in these plants when shifted to peat moss-containing pots; the plants supplemented with higher levels (5.0 mg L⁻¹) of IBA showed maximum (25.62 ± 1.41 cm) root growth which was gradually decreased to minimum (9.81 ± 0.46 cm) with decreasing concentrations (from 5.0 to 0.0 mg L⁻¹) of supplementary IBA, confirming that the root development is inversely and directly proportional to increasing concentrations of IBA under in vitro and in vivo conditions, respectively. Hence, plants treated with IBA under in vitro conditions develop more established roots upon transplanting to open environment, suggesting that supplementary IBA is desirable for establishment of root system and for adaptation of in vitro grown and/or engineered Saccharum clones to open environment without compromising the mortality of transplants.