Factors influencing conventional and semi-automated micropropagation

Several factors influence the different stages of micropropagation. For culture initiation, the choice of surface sterilisation agents can greatly affect the success of in vitro establishment. The most commonly used sterilisation agent is sodium or calcium hypochlorite. However for many woody species, only mercuric chloride could overcome contamination as shown for Hagenia abyssinica. For hairy material like Saintpaulia, hydrogen peroxide was more effective than calcium hypochlorite. Shoot multiplication is generally affected by type and concentration of growth regulators. For some species like Syringa, efficient shoot multiplication was only obtained by using nodal explants of elongated shoots which can be obtained by addition of the sugar alcohol mannitol. Mother plant treatment could sometimes influence shoot regeneration as shown in Begonia cheimantha. Rooting requires the growth regulator auxin. Some species have enough endogenous auxin content for root induction but most species require exogenous application. Moreover, for several woody species, a number of subcultures are required before the shoots are able to respond to exogenous auxin as shown in the apple cultivar Akero. In order to optimise the auxin concentration and time of exposure, we have used a special rooting system-thin stem discs. We have shown that the use of temporary immersion system for micropropagation of several fruit species as well as woody species has reduced labour costs significantly. Although there are still problems associated with the technique there is no doubt that temporary immersion systems will play a dominant role in future micropropagation of plants.