The influence of stockplant fertilization on tissue concentrations of nitrogen, carbohydrates and amino acids and on the rooting of leafy stem cuttings of Cola anomala K. Schum (Malvaceae)

Agroforestry tree domestication for forest restoration and fruits and nuts production is ongoing in West and central Africa. It is focused among others on vegetative propagation techniques to capture the superior phenotypes of individual trees. Cola anomala which is a priority target for domestication has been reported amenable to vegetative propagation through rooting of leafy stem cutting, but the rooting efficiency of cuttings collected from non-fertilized stockplants was very poor. The present study addressed the effect of a range of granular NPK 20-10-10 doses (0, 0.5, 1, 2, and 5 g/plant applied at 2-month intervals for 8 months) on growth, total nitrogen content, available carbohydrate content and amino acid content of C. anomala stockplants and the subsequent rooting ability of leafy stem cuttings. Results showed that perseverance fertilizer applications significantly affected growth (p < 0.001), nitrogen content (p < 0.001), carbohydrate content (p = 0.003) and amino acid content (p = 0.001) of stockplant shoots, as well as mortality percentage (p < 0.001), rooting percentage (p = 0.04) and the number of roots (p = 0.02) of subsequently harvested cuttings. The lowest mortality rate (0 %) was associated with the highest rooting percentage (90 ± 7.1 %), while the highest number of roots per rooted cutting (2.61 ± 0.31) was obtained when NPK fertilizer was applied at the rate of 1 g/plant. This dose corresponded to the rate at which stockplant growth was maximized. Of the parameters investigated, only the content of available carbohydrate at the time of excision was significantly correlated with percentage of cuttings rooted (r = 0.90, p = 0.03) and the number of roots per rooted cutting (r = 0.90, p = 0.03). It is concluded that NPK fertilizer applied to stockplants at the rate of 1 g/plant at 2-month intervals for 8 months resulted in the fastest growth and the best rooting ability of subsequently rooted cuttings. This is valuable information to optimize the clonal propagation protocol for C. anomala and other species of the humid tropics of West and Central Africa, especially those considered to be difficult to propagate.