Abstract
Melia volkensii is a tree species growing in semi-arid regions of East Africa, and is recognized as one of the most valuable forestry species in such regions of Kenya. The use of root cutting is an easy method for its clonal propagation, but the most appropriate conditions have not been systematically examined. In this study, the relationship between diameter of root cut edge or fresh weight and formation frequency of adventitious bud were assessed. In addition, roots were divided into two fragments, and formation frequency of adventitious bud was compared between cross-sections roots without root tip and roots with root tip. Both the diameter of the cut edge and fresh weight of roots forming adventitious buds were significantly higher than in those not forming them (unpaired t-test, p<0.01). Formation frequency of adventitious bud was 77.0% in roots satisfying the criteria of cut edges diameter >15 mm and fresh weight >20 g, but it decreased (37.2%) in roots that did not meet this criteria. Based on anatomical analysis, an effect of the developmental stage of root fragments on adventitious bud formation was suggested, and root size is thought to reflect the stage of root development. The formation frequency of adventitious buds was 72% even in cross-sectioned roots, and the proportion was not significantly different from that of normal root tip (p>0.05). Therefore, it is concluded that root cutting using cross-sectioned roots are also available for clonal propagation. Key words: Clonal forestry, anatomical analysis of root, availability of cross-sectioned roots.
Highlights
Nodular and compact callus formation was observed within two to four weeks on most roots eventually forming adventitious buds (Figure 1c); adventitious buds developed from the callus (Figure 1d)
Adventitious buds were observed in 50 out of 94 roots (53.2%). Both the diameter of the cut edge and fresh weight were significantly different between roots that formed adventitious buds and those that did not form them (p < 0.01), and roots that formed adventitious buds were larger than those that did not form them (Figure 4)
Effect of sectioning of root cutting on adventitious bud formation
Summary
The tree is recognized as one of the most valuable species for agroforestry purposes in the area because of features such as its drought tolerance, fast growth, high wood quality and ant resistance (Kariuki et al, 1990; Mulanda et al, 2015). Superior varieties will be developed in the near futures, and the availability of clonal propagation protocol has important implications in the distribution of these varieties. This is because cloned trees maintain the genetic makeup of their mother trees, and the use of clones with homogeneous and desirable traits will improve productivity in forestry and agroforestry (Park et al, 1998; McKey et al, 2009). Other easy and costeffective method for clonal propagation is needed for M. volkensii
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