Genotyping by Sequencing Reveals Genetic Relatedness and Duplicates amongst Local Cassava (Manihot esculenta Crantz) Landraces and Improved Genotypes in Kenya

Abstract

Future demand for cassava is expected to increase in order to mitigate climatic changes, sustain food security and provide raw materials for industry. To meet these demands, adoption of modern omics methods ensures reliability, precision and timely delivery of more productive and resilient varieties. A total of 112 mix of duplicate clones, diverse local cassava landraces (LARs) and improved genotypes (IMGs) were genotyped using single nucleotide polymorphisms (SNPs) generated through genotyping by sequencing (GBS) approach. About 17% (5808) of the 33672 SNPs were used for hierarchical clustering and ADMIXTURE analysis for ancestries. Approximately 48 and 52% of the germplasms respectively formed 17 independent clusters (identical clones or duplicates) and admixtures (unique or non-duplicated clones). Of the duplicates, 10 clusters were formed from LARs, four from IMGs and three from a mix of both LARs and IMGs, revealing their genetic relatedness. Approximately 71 and 29% of clusters comprised cassava accessions from the same and different geographical regions, respectively, with the geographical restriction of clusters attributed to the limited movement of planting materials across the country, possibly due to a weak seed distribution system or disease-driven quarantine measures. The historical sharing or exchange of stakes or stem cuttings by farmers was linked to the duplication of LARs, whereas IMGs duplication may be associated with convergent evolution, selection, or sharing of common parentage. The high number of admixtures or unique clones implied minimal loss of genetic diversity. These findings can aid designing efficient and effective cassava improvement programs through development of a core set of diagnostic markers.