VARIATIONS IN THE YIELDING ABILITY OF SWEET-POTATO CLONES IN GRASSLAND AND FOREST ECOLOGIES IN CAMEROON

Twenty sweet potato genotypes were evaluated for four years in seven locations representing three agro-ecological zones in Cameroon, to study their performance across environments, to identify cultivars suitable for the different zones and to study their reaction to weevils and viruses in target sites. The best storage root yields (13.3 t ha(-1)) were in the humid forest region and the lowest (7.4 t ha(-1)) in the grassland region. Storage root counts were about the same in the humid forest and in the grassland regions. Root yields were not affected by weevil attack, but virus severity was associated with storage root field depression. Shukla's stability method was less conservative than the Eberhart-Russell method of assessing stability. The genotype grouping technique of Francis and Kannenberg was considered easier to use in grouping clones into classes of desirability and stability. The study suggests that it may not be necessary to select separately for different agro-ecological zones because high yielding cultivars of sweet potato developed for one zone are most likely to be adaptable to other zones.