View/Open - ResearchSpace - University of KwaZulu-Natal

Literature review
from insects appears as tracks across the medium which are visible due to
surrounding fungal or bacterial growth (SMITH, 2000b).
Explant material may harbour internal micro-organisms (SMITH, 2000b). In such a
case, it is very difficult to establish clean cultures. Explants that are least likely to
harbour internal contaminants include explants taken from growing shoot tips, ovules
of immature fruit, immature and mature flower parts and runner tips (SMITH, 2000b).
Explants that are more likely to harbour internal contaminants include explants taken
from bulbs, slow-growing shoots or dormant buds, roots, corms and underground
rhizomes (PIERIK, 1997; SMITH, 2000b). In such cases seeds are often aseptically
germinated to provide clean explants from the root, hypocotyl, cotyledon and shoot
(PIERIK, 1997). In these situations the use of antibiotics or fungicides in the medium
is generally not useful (SMITH, 2000b). Although these agents can repress the
growth of some microorganisms, they can also suppress the growth of the plant
tissue or even kill it (SMITH, 2000b).
2.9.3 Medium composition
A number of standard formulae for tissue culture media have been developed to
provide optimum nutrients and growth regulators for specific plants (KYTE & KLEYN,
1996). The selection or development of a suitable culture medium is vital to the
success of the culture (SMITH, 2000b). The approach to the development of a
suitable medium will depend on the purpose of the culture (SMITH, 2000b).
The medium generally contains water, inorganic salts, plant growth regulators,
vitamins, a carbohydrate and a gelling agent (SMITH, 2000b). High quality water
should be used as an ingredient of the plant culture media (PIERIK, 1997; BEYL,
2005). Ordinary tap water contains cations, anions, particulates, micro-organisms
and gases that may influence the reaction of the tissue culture media with the tissue
(BEYL, 2005). The most commonly used method of water purification involves a
deionization treatment followed by one or two glass distillations (PIERIK, 1997;
BEYL, 2005).
67