Handicaps for the large scale commercial application of micropropagation.

In the last 10 years micropropagation has shown a spectacular development. However, at present the widespread use of micropropagation is handicapped by the following facts: Frequently mutations occur, particularly when applying the adventitious bud technique and callus systems. Basic knowledge concerning factors affecting organ and somatic embryo formation in various types of cultures is often completely lacking. Woody species (shrubs and trees) are extremely difficult to clone in vitro because rejuvenation can often not be induced; rooting of adult shoots is hardly possible. Internal infections are still a serious handicap for commercial application. Problems as vitrification (a physiological disease) and exudation of toxic compounds in the medium can hardly be solved. In vitro (a relatively closed system) ethylene and carbon dioxide levels can increase to an unacceptable level, often resulting in plants of bad quality. The role of the physical growth factors (light, temperature, humidity, the gas phase) is strongly neglected. During the transfer from test tube or container to soil a high percentage of the plants can be lost, because the micropropagated plants are not well adapted to the in vivo climate. Mass propagation in vitro is very labour intensive, resulting in too high a cost price. Real possibilities for mechanization are still missing. The techniques developed are not always economically viable and therefore rejected. During large scale micropropagation timing of production is often insufficiently controlled