Assessment of genetic diversity, combining ability, stability and farmer preference of cassava germplasm in Ghana

[摘要] English: The aim of this study was to assess genetic diversity, combining ability, heterosis, heritability oftraits, stability and farmer preference of cassava germplasm in Ghana in order to structure aneffective breeding programme. The assessment of genetic diversity in a collection of localcassava genotypes using 33 SSR markers revealed a high overall heterozygosity. The SSRmarkers identified 63 duplicates in the collection. The heterotic pools were distinct for thesavannah and the forest ecological zones and this was the basis for the selection of progenitorsfor the rest of the study. Seven and five cassava progenitors were crossed in a diallel designwithout reciprocals in the forest and savannah ecologies respectively. The progenitors andprogenies were evaluated for CMD, CBB, yield and its components in two seasons in the forestand one season in the savannah zone. The GCA:SCA ratio indicated that the GCA was largerthan SCA for average root number, indicating additive gene effects and a possibility forimprovement by selection. SCA was larger than GCA for harvest index and fresh root yield,indicating environmental effects on the trait and confirms the non-additive effects mainlydetermining expression of root yield. The parental genotypes were selected from a particularregion where CMD is the main economic constraint. Debor had the best GCA effect for cassavamosaic severity reaction; while Tuaka had the best GCA effect for fresh root weight. Debor xKwasea was the best combination for CMD resistance. Debor and Kwasea were the best parentsfor resistance breeding to CMD. The predictability ratio varied between 0.58 and 0.84. CMD androot number had a ratio close to one for the savannah and forest zones, showing that these traitswere highly heritable and influenced by additive gene action. Marker assisted selection was usedto search for new sources of CMD resistance in the progenies and progenitors. Crosses amongCIAT elite genotypes and landraces revealed progenitor Dabodabo as a putative source of newgenes to CMD resistance.

[发布机构] University of the Free State