Agronomic Performance and Susceptibility of Seven Ghanaian Improved Sweet Potato Varieties to the Sweet Potato Weevil, Cylas spp. (Coleoptera: Brentidae) in Coastal Savanna Zone of Ghana

Abstract

Sweet potato (Ipomoea batatas (L.) Lam. is an important food crop adaptable to a broad range of agro-ecological conditions. The knowledge of the performance of the available varieties under a specific ecological condition is important to improve the production. A field experiment was carried out at the University of Ghana farm during the major and minor rainy seasons of 2015 to determine the yield performance of seven improved Ghanaian sweet potato varieties (CRI-Apomuden, CRI-Ligri, Faara, CRI-Bohye, CRI-Dadanyuie, Okumkom, Sauti) and their susceptibility to the sweet potato weevil, Cylas spp. (Coleoptera: Brentidae). Significant difference was found in the storage root yield among the varieties, with CRI-Ligri having the highest in both major (23.11 t/ha) and minor (22.49 t/ha) rainy seasons. CRI-Apomuden and CRI-Ligri scored the highest levels of infestation by sweet potato weevil in the major and minor seasons (1.94 and 2.00, 1.84 and 1.96, respectively) and yield loss (44.44 % and 42.80 %, 23.84 % and 23.87 %, respectively). While the lowest infestation levels in the major rainy season were recorded on Faara and Okumkom (1.18 and 1.31, respectively) with yield losses of 10.32 % and 9.09 %, respectively. However, in the minor rainy season, there was no significant difference among Faraa, Okumkom, CRI-Bohye and CRI-Dadanyuie in terms of infestation level and yield losses. Significant difference was found in all measured root characteristics including the shortest weevil distance, root neck length, root length, root girth and root size index. The storage root infestation had a strong negative correlation with the shortest weevil distance, a strong positive correlation with the root size index and a weak negative correlation with root neck length. In this study, Okumkom appeared to be less susceptible to sweet potato weevil infestation with relatively acceptable yield performance and therefore can be recommended for use by farmers to improve sweet potato production.