Genetic diversity of cassava (Manihot esculanta crantz) germplasm and effect of environment on resistance to Cassava Brown Streak and Cassava Mosaic Diseases in Burundi

IITA supervisor: Dr. Tumwegamire, S.Cassava is an important cash crop for many small scale farmers in Burundi. Most small scale farmers use local landraces and though they have farmer preferred traits, their genetic diversity is unknown and marred by phenotypic susceptibility to Cassava Brown Streak Disease (CBSD) and Cassava Mosaic Disease (CMD). This limits future breeding programs to improve cassava production and resistance to diseases in Burundi. Due to this, disease tolerant genotypes from other countries were introduced to Burundi to help improve on their germplasm and then determine the relationships between local landraces and improved germplasm. Objectives of this study were to (1) assess the genetic diversity among cassava landraces and introduced cassava genotypes using morphological and molecular markers, (2) determine effects of genotype by environment (GxE) interaction on resistance to CBSD and CMD diseases in varied agro-ecological zones of Burundi. Genotype characterization was done using 17 qualitative agro morphological traits while molelcular analysis was conducted using SNP genotyping data from DaRTseq using KDCompute on 118 genotypes. For objective 2, the effect of GxE interaction on resistance to cassava viral diseases was determined using 18 accessions arranged in alpha lattice design on 9 blocks per site. Data was taken on sprouted cuttings, whiteflies population, foliar diseases, root necrosis, growth parameters and yield. Results for objective 1, on 118 accessions revealed more than 18,000 SNPs but there with low genetic distance (Fst