Abstract

The effect of different auxin concentrations, leaf areas and propagation media on the rooting ability of leafy stem cuttings of Milicia excelsa were investigated using a non-mist propagation system in Ghana. Three separate experiments tested (i) indole-3-butyric (IBA) concentrations ranging from 0.0 to 1.6%, (ii) leaf area treatments of 0, 10, 20, 40 and 60 cm2 obtained by trimming the leaves, and (iii) four propagation media, namely fine sand (diameter 2 mm or less), coarse sand (2–4 mm), decomposed sawdust and a 1:1 mixture of coarse sand and sawdust. In each experiment, cuttings were taken to a standard length of 6 cm from shoots of previously pruned pot-grown stockplants grown under 40% shade. IBA had no significant effect on final rooting percentage (P > 0.05, ANOVA), although values declined with successive increases in IBA concentration above 0.2%. Addition of IBA increased root number by approximately 80%, but was also positively correlated with cutting mortality (r = 0.81, P < 0.05). Percentage rooting and root number were positively related to leaf area (r = 0.89 and 0.90, respectively, P < 0.05), whereas shoot production, leaf abscission and mortality decreased significantly (P < 0.05) with increasing leaf area. highest rooting percentages and root numbers were recorded in sawdust. Overall, moisture content of the media was positively related to root number (r = 0.98, P < 0.05), but negatively related to mortality and leaf abscission. Foliar relative water content (RWC) increased in all experiments during the first 2 weeks after insertion by 1.3–15.3%, higher values being recorded in media with a sawdust component. These results suggest that an application of not more than 0.2% IBA should be used for mass propagation of Milicia excelsa cuttings, with a leaf area of around 40 cm2 and a medium with a high moisture holding capacity (24% or less water by volume).