Effect of grafting and pruning on flowering and seed set in cassava (Manihot esculenta Crantz)

Abstract

Seed setting is a major constraint to cassava improvement. Some varieties set seed and others rarely set seed because they have poor flowering patterns. This limits inclusion of some would be elite genotypes in conventional cassava improvement through crossing breeding. Increasing flowering is important as it facilitates routine cross-breeding operations in nurseries, reducing operating costs and speeding up the production of segregated populations. Grafting and leaf pruning were reported to enhance flowering, fruit and seed production in other plants and crop species. The aim of this study was to enhance profuse flower induction and seed set in poor flowering cassava genotypes in order to make them available for use in breeding programmes. The specific objectives were: i) to determine the effect of grafting on flowering and seed-set in cassava, and ii) to establish the effect of pruning on flowering and fruit-set in cassava. Field and screen house experiments were conducted at National Crops Resources Research Institute - Namulonge and at National Forestry Resources Research Institute – at Kifu, Mukono. To evaluate the effects of grafting on flowering, fruit-set and seed emergence, a randomized complete block experimental design with three replications was used. A split plot design with three replications was used to test the effect of leaf removal on flowering and fruit-set. The poor flowering and seed setting variety TME204 was grafted on to high flowering and good seed-setting variety NASE14. Self-grafts and non-grafted plants of each genotype were included as controls. Data was collected on branching habit, number of; inflorescence, male flowers, female flowers, flower stalks, fruits, seeds set and seed emergence. Results obtained showed significant (P < 0.001) variation among the graft combinations for the number of female and male flowers. Pruning intervals were highly significant (P<0.001) for the number of inflorescences, flower stalks, female flowers and male flowers and at P<0.01 for the number of fruits. Non-grafted NASE14 and whip self-grafted TME204 had the least seed emergence percentages (22.3%). Highest seed emergence (68.9%) was realised for non-grafted TME204. Grafting and leaf pruning did not enhance flowering, fruit-set and in cassava genotypes used in this study. Cassava meant for crossing should not be pruned. Other flower induction techniques could be used.