Genotypic Effect of Rootstock and Scion on Grafting Success and Growth of Kola (Cola nitida) Seedlings

Abstract

Kola (Cola nitida) is an important economic cash crop for many West and Central African countries. It has several medicinal uses in the pharmaceutical industries and also plays a major role in traditional marriages among Islamic communities across West and Central Africa. The crop is extensively cultivated in Nigeria and Ghana. However, it exhibit signs of total and partial sterility as well as self incompatibility when propagated from seeds in most cases. Therefore, grafting is seen as a method of choice in addressing the problem stated above. Though grafting accounts for some degree of success, there is the need to assess genotypic and physiological factors that account for high or low grafting success. Genetic and physiological factors (such as rootstock age) affecting grafting success and growth in kola (C. nitida) were investigated in two separate experiments. In experiment I720 kola seedlings were raised from unselected kola nuts and sown at two monthly intervals. Four groups of seedlings (180/group) i.e. 6, 8, 10 and 12 months old were thus produced. Three different scions (A1, A12 and JB1) measuring (5-10 cm) were grafted onto the four age groups of rootstocks, namely, 6, 8, 10 and 12 months. Experiment II consisted of 540 seedlings raised from three main crosses (JX1/9 × JX1/11 * B1/142 × B1/151, JX1/9 × JX1/11 * B2/177 × B2/156 and JX1/9 × JX1/11 * GX1/46 × GX1/53). Grafting was done after six months using the same set of scions as described in experiment I. Experimental design used was 3 × 4 and 3 × 3 factorial designs in completely randomised design with three replicates for experiment I and II respectively. The fixed effects were the different genotype and age of rootstock at grafting whilst the response variable was the percentage of successful grafting two months as well as growth at six monthly intervals. Results from the study showed that grafting onto 6 months old stocks gave the highest percentage success and growth of grafts followed by 8, 10 and 12 months old rootstock in that order in both trial years. The study revealed also a significant rootstock and scion interaction (P < 0.05). We conclude that successful grafting in kola depends on rootstock genotype such as JX1/9 × JX1/11 * GX1/46 × GX1/53 and has been proven suitable for use in future kola propagation studies. Nonetheless, suitable rootstock with high grafting success does not translate into vigorous scion growth.