Vegetative propagation of Milicia excelsa by leafy stem cuttings: effects of auxin concentration, leaf area and rooting medium

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).