Genetic studies on iron and zinc concentrations in common bean (Phaseolus vulgaris L.) in Ghana.

Iron and zinc deficiencies cause high health risk to young children and expectant mothers in sub Saharan Africa. The development of biofortified common bean (Phaseolus vulgaris L.) varieties could address the acute micronutrient deficiencies with associated improvement in the nutrition and health of women, children and adults. The objective of this study was to determine the mode of gene action and genetic advance in iron and zinc levels in common bean. Field experiment was carried out using six generations of two populations made of crosses between pairs of low iron, low zinc and high iron, moderate zinc genotypes (Cal 96 Ë£ RWR 2154; MCR-ISD-672 Ë£ RWR 2154). Each generation (P1, P2, F1, F2, BC1P1 and BC1P2) was evaluated on the field in a randomized complete block design with three replications. Generation mean analysis were performed for each trait measured in each of the crosses while iron and zinc levels were quantified by x-ray fluorescence. The study showed that both additive and non-additive gene effects were important in determining the expression of high iron and zinc levels. Iron concentration in the common bean seeds ranged from 60.68 to 101.66 ppm while zinc levels ranged from 25.87 to 34.04 ppm. Broad sense heritability estimates of iron and zinc were high in the two crosses (62-82% for Fe and 60-74% for Zn) while narrow sense heritability ranged from low to high (53-75% for Fe and 21-46% for Zn). Heritability and genetic gain were used as selection criteria for iron and zinc, and it was concluded that doing so would be beneficial for future improvement.

High-density DArT-based SilicoDArT and SNP markers for genetic diversity and population structure studies in cassava (Manihot esculenta Crantz).

Cassava (Manihot esculenta Crantz) is an important industrial and staple crop due to its high starch content, low input requirement, and resilience which makes it an ideal crop for sustainable agricultural systems and marginal lands in the tropics. However, the lack of genomic information on local genetic resources has impeded efficient conservation and improvement of the crop and the exploration of its full agronomic and breeding potential. This work was carried out to obtain information on population structure and extent of genetic variability among some local landraces conserved at the Plant Genetic Resources Research Institute, Ghana and exotic cassava accessions with Diversity Array Technology based SilicoDArT and SNP markers to infer how the relatedness in the genetic materials can be used to enhance germplasm curation and future breeding efforts. A total of 10521 SilicoDArT and 10808 SNP markers were used with varying polymorphic information content (PIC) values. The average PIC was 0.36 and 0.28 for the SilicoDArT and SNPs respectively. Population structure and average linkage hierarchical clustering based on SNPs revealed two distinct subpopulations and a large number of admixtures. Both DArT platforms identified 22 landraces as potential duplicates based on Gower's genetic dissimilarity. The expected heterozygosity which defines the genetic variation within each subpopulation was 0.008 for subpop1 which were mainly landraces and 0.391 for subpop2 indicating the homogeneous and admixture nature of the two subpopulations. Further analysis upon removal of the duplicates increased the expected heterozygosity of subpop1 from 0.008 to 0.357. A mantel test indicated strong interdependence (r = 0.970; P < 0.001) between SilicoDArT and DArTSeq SNP genotypic data suggesting both marker platforms as a robust system for genomic studies in cassava. These findings provide important information for efficient ex-situ conservation of cassava, future heterosis breeding, and marker-assisted selection (MAS) to enhance cassava improvement.