Synergistic interaction of exogenous auxin and reduced level of stockplant irradiance on the rooting of cola acuminata (Pal. De Beauv.) stem cuttings: applications for agroforestry trees domestication

ABSTRACT The establishment of an efficient propagation protocol is one of the most important steps in the domestication of agroforestry trees. Using Cola acuminata as a biological model, the present study investigated the interaction between exogenous auxin and reduced levels of stockplant irradiance for its effect on the rooting of stem cuttings. In a 3 × 4 factorial experiment, three levels of stockplant irradiance and four concentrations of indole 3-butyric acid (IBA) were tested for their effect on the rooting potential of leafy stem cuttings. Relationship between flavonoid content of stockplants and rooting potential of stem cuttings was also investigated. Results showed that percentage of cuttings rooted significantly increased, as did the mean number of roots, with decreasing levels of stockplant irradiance. Likewise, rooting was enhanced by all applications of IBA. 100% rooting was achieved under the combination of 50% and 25% ambient irradiance together with 2% and 4% IBA. The mean number of roots was greatest (11.4 ± 0.2) when 4% IBA was combined with 25% ambient sunlight. Flavonoid content of plant extracts decreased with stockplant irradiance. There were significant negative correlations between flavonoid content of plant extracts and the rooting parameters of cuttings.