Abstract
Inbreeding coefHcients (F) in sweet potato breeding materials were computed and the relationship between yield and F value was studied. The purpose of this study was to determine how high F value was tolerable for high-yeild breeding because it is now practically impossible in sweet potato breeding to make crosses between parents having no common ancestors in their pedigrees. Yield data were from the yield tests of seedling clones for 20 years. F values of 890 breeding materials were computed. The number of ancestors and the maximum generation in each pedigree were counted to give the outline of the pedigree. The number of ancestors in a pedigree (number of cultivars in a pedigree tree) was counted by two methods : one method (total number of ancestors) involved counting total ancestors, i.e., counting twice when one cultivar appeared twice and counting three times when it appeared three times in a pedigree. The other method (number of ancestors "except common ones") counted a cultivar only once even though it appeared more than once in a pedigree. Maximum generation in a pedigree means, for example, when the "last" ancestor is a grandparent. it is 2, and when the last ancestor is a grat-grandparent, it is 3.
