Genetic variability of sorghum landraces from lower Eastern Kenya based on simple sequence repeats (SSRs) markers

The aim of this study was to estimate the genetic variability of sorghum landraces grown in lower eastern Kenya based on simple sequence repeats (SSRs) markers. A total of 44 landraces obtained from the farmers and four improved varieties were analyzed using 20 SSR markers. All markers were polymorphic with polymorphism information content (PIC) value ranging from 0.04 to 0.81 with a mean of 0.49. Heterozygosity ranged from 0.00 to 0.04 suggesting that each detected a single genetic locus and that each of the sorghum accession used was stable. The alleles ranged between 2 and 10 and an average of 5.05 alleles per primer pair. The gene diversity ranged from 0.04 to 0.83 with a mean value of 0.53. All possible allele combinations ranged from 2 to 10, while major allele frequency ranged from 0.32 to 0.98. Genetic distances varied from 0.15 to 0.90 with two genotypes Karuge 1 and Karuge 2 obtained from Kiritiri in Mbeere having the minimum (0.15) and indication of very close relatedness. The diversity of the landraces was structured more on geographical locations and on seed colorations than agroecological conditions. Such intraregional genetic proximity in sorghum landraces would arise through seed exchanges among farmers. Analysis of molecular variation indicated higher variation within populations than among the groups. The genetic diversity can be exploited in hybridization programs to improve sorghum varieties grown by farmers in semi arid areas.Key words: Genetic variability, landraces, simple sequence repeats, sorghum

High-resolution linkage map and chromosome-scale genome assembly for cassava (Manihot esculenta Crantz) from 10 populations

Cassava (Manihot esculenta Crantz) is a major staple crop in Africa, Asia, and South America, and its starchy roots provide nourishment for 800 million people worldwide. Although native to South America, cassava was brought to Africa 400–500 years ago and is now widely cultivated across sub-Saharan Africa, but it is subject to biotic and abiotic stresses. To assist in the rapid identification of markers for pathogen resistance and crop traits, and to accelerate breeding programs, we generated a framework map for M. esculenta Crantz from reduced representation sequencing [genotyping-by-sequencing (GBS)]. The composite 2412-cM map integrates 10 biparental maps (comprising 3480 meioses) and organizes 22,403 genetic markers on 18 chromosomes, in agreement with the observed karyotype. We used the map to anchor 71.9% of the draft genome assembly and 90.7% of the predicted protein-coding genes. The chromosome-anchored genome sequence will be useful for breeding improvement by assisting in the rapid identification of markers linked to important traits, and in providing a framework for genomic selectionenhanced breeding of this important crop.Bill and Melinda Gates Foundation (BMGF) Grant OPPGD1493. University of Arizona. CGIAR Research Program on Roots, Tubers, and Bananas. Next Generation Cassava Breeding grant OPP1048542 from BMGF and the United Kingdom Department for International Development. BMGF grant OPPGD1016 to IITA. National Institutes of Health S10 Instrumentation Grants S10RR029668 and S10RR027303.http://www.g3journal.orghb201