The effect of conditioning Acacia mearnsii De Wild. hedge-plants under shadenetting on rooting, elemental uptake and productivity of cuttings

Abstract

Acacia mearnsii is a commercial forestry tree in South Africa, largely grown from open-pollinated seeds. Clonal deployment of superior selections of the species is restricted due to its poor rooting ability. The effects of conditioning parent hedge-plants under three levels of reduced light (80% black; 60% red and 40% black/ white shadenet) were investigated. Hedge-plant nutrition, carbohydrate content, productivity and rooting of cuttings were measured. Conditioning hedge-plants under 80% black shadenet for five weeks gave the highest rooting percentages in both seasons (39.3% and 22.1%) (p < 0.05), despite having a lower productivity of 42.5 cuttings per hedge-plant (p > 0.05). As the shading increased to 80% black, so the rooting increased, and stem/leaf total non-structural carbohydrate levels decreased (r = −0.61 to −0.97). Conditioning under shadenet reduced leaf and increased stem total macronutrient percentages but increased both leaf and stem total micronutrient concentrations. Total macro- and micronutrient levels were greatest after conditioning under 80% black shadenet, except for stem-nitrogen, stem-carbon and leaf-manganese, which had the lowest values (p > 0.05). In conclusion, hedge-plant conditioning under 80% black shadenet can significantly improve rooting of A. mearnsii cuttings, which could facilitate the commercial clonal propagation of the species.