THE EFFECTS OF PLANT HORMONES ON ROOT INITIATION

Thesis Overview

INTRODUCTION

Ginger (Zingiber officinale Rosc) is a perennial herb that grows from underground rhizomes. The rhizomes are often mistakenly called the “roots”. Botanically, it is the rhizome that is characterised with the slightly hot, citrus-like taste and aroma. Ginger belongs to the family, Zingiberaceae. Members of the family are mostly advance monocotyledonous plants and are rhizomatous herbs. They are found throughout the tropical and subtropical regions but are mainly distributed in Asia. Ginger is the tenth most important spice in the world (McGee, 2004). Ginger rhizomes are used in pharmaceutical industries. It is rich in secondary metabolites such as oleoresin (Bhagyalakshmi and Singh, 1988). The demand for fresh and dry ginger and its essential oil in the world market is high. Ginger is propagated vegetatively using underground rhizomes. Most farmers use planting materials saved from previous harvest. These materials could have been sold for cash. Contingent on this, many farmers are reluctant to use healthy succulent rhizomes for planting. These are rather sold thereby resulting in shortage of planting materials.

Tissue culture technique can be applied to mass-produce seedlings for distribution to ginger farmers. This however, is not cost effective now due to lack of the necessary materials required for tissue culture. Most of the materials for tissue culture are not locally available and are therefore procured at high amount. One of such materials is the gelling agent, agar. Agar represents one of the most expensive tissue culture media components. It is widely used for preparing solid and semisolid plant tissue culture media because it withstands temperatures of about 1000C without being denatured (Scholten and Pierik, 1998). Therefore, establishment of plant micro propagation laboratories must be based on cost effectiveness. Gelatin that is cheaper when used at a concentration of 100g/1 is currently not widely used because it denatures at 250C. Methocel (methyl cellulose) an alginate is also cheaper than Agar. However, Adaoha and Roscoe (1982) observed that there are two disadvantages associated with the use of alginates. The first is that solutions cannot be autoclaved without alginate breakdown during sterilization at high temperatures. The second disadvantage is that, alginate reacts with divalent metal cations (Be2+, Mg2+, Zn2+, Cd2+, Hg2+ and Pb2+) which may cause nutrient deprivation.

It is on the basis of these considerations that the present research was set up to develop a locally available and cheap protocol that is reproducible in ginger plant tissue culture work with the following objectives:

OBJECTIVES OF THE STUDY

1. To determine the best pre-initiation treatment for in-vitro ginger multiplication.
2. To determine the effect of plant growth hormones – auxin and
cytokinin on in-vitro propagation of ginger using agar as a gelling agent.
3. To compare agar gelled medium with cassava gelled medium in in-vitro propagation of ginger at the initiation stage.