Conifer micropropagation: its function in tree improvement programs

Abstract

In contrast to herbaceous crops, many of which are propagated in vitro on a commercial scale, micropropagation of many tree species, especially conifers, is still largely experimental. Among the hardwoods, a number of orchard and ornamental trees and a few forest species can now be micropropagated on a commercial scale. However, large-scale micropropagation is, at present, possible with only one or two conifers species. One reason for the lack of commercialization of conifer micropropagation is cost. To be of use for large-scale reforestation, the cost per micropropagule would have to be reduced to a value close to that of a seedling [19]. Furthermore, micropropagules sometimes show signs of early maturation and other abnormalities. Considering these problems, micropropagation generally does not yet compare favorably with traditional rooting of cutting techniques. In some species, the efficiency of traditional rooting of cuttings techniques can be further improved by spraying ortet seedlings with benzylaminopurine. This stimulates shoot formation from axillary buds and thus results in an increase in the number of shoots available for conventional rooting of cuttings [20,28,31]. In those species where such additional shoot production is possible, the competitiveness of micropropagation vis à vis rooting of cuttings is even further eroded.