Abstract:

Sweet potato (Ipomoea batatas (L.), a hexaploidy, self-incompatible species with2n=6x=90 chromosomes, is the seventh most important food crop in the world. Uganda is the third largest global producer after China and Nigeria, and a secondary center of diversity where subsistence farmers mostly grow it as a starchy staple for food security. Through a purposive sampling of 21 districts of Uganda, a total of 1303 sweet potato accessions with 565 vernacular names were collected from farmers’ fields in 171 sub-counties. Great variations were observed in the numbers of accessions grown in the different districts and morphological characteristics in the farmers’ fields. The level of morphological variation as estimated using the Shannon Weaver diversity index (H1) for the traits ranged from 0.10 to 0.99 with an overall mean of 0.71±0.03, an indication of high diversity. Cluster analysis using the unweighted pair-group method using arithmetic averages (UPGMA) grouped 1256 of the accessions into 20 major clusters and many sub-clusters and classified 899 accessions as morphologically distinct and 357 as duplicates. The morphologically distinct genotypes differed significantly for yield, dry matter content, sweet potato virus disease and Alternaria blight resistance (p=0.05). Most of the genotypes had mean total root yields of less than 20.0 t/ha, low specific gravity values of less than 2.0, and low disease resistance. A total of 192 superior genotypes were selected for further evaluation and use in hybridization schemes and variety development. Ten fluorescent-labeled simple sequence repeat (SSR) markers were used to assess the genetic relationships among the superior genotypes. The mean pair-wise genetic distance among the 192 genotypes was 0.57, an indication of high genetic diversity. The 192 genotypes were grouped into four major clusters. The SSR markers used in the study were highly informative with average polymorphic information content (PIC) of 0.62. Two duplicate genotypes were identified through SSR genotyping. The genetic potential of sweet potato germplasm in Uganda has been understood through this study.