SIMPLE SEQUENCE REPEAT (SSR) GENETIC ANALYSIS OF CASSAVA MOSAIC DISEASE RESISTANCE IN SELECTED F1 POPULATIONS OF CASSAVA

Thesis Abstract

Cassava mosaic disease caused by begomoviruses is the most widespread disease of cassavain Africa. Simple sequence repeat (SSR) genetic analysis of an F1 population of cassava wascarried out to identify new sources of CMD resistance. Genomic DNA extracted from parentsand progeny was amplified using polymerase chain reaction (PCR).The broad objective of the study was to investigate the socio-economic andcultural dimensions of food security among selected ethnic groups in North CentralNigeria. Specifically, the study was designed to determine food culture and practices ofthe respondents; determine the household food security status (energy availability) acrossethnic groups; determine dietary diversity of the households across cultures; identifyperceived constraints militating against household food security; and describe the copingstrategies utilized by the households during food shortages. Seven hypotheses and aconceptual framework were developed for the study. The population of the study consistsof all ethnic groups in North Central Nigeria. The zone comprises about 60 ethnic groups.Specifically, the study was carried out among Tiv, Igala and Eggon ethnic groups ofBenue, Kogi and Nasarawa States. A multi-stage sampling technique was adopted for thestudy. Three ethnic groups (Tiv, Igala and Eggon) and one village per ethnic group PCR amplifications wererun on polyacrylamide and agarose gels. SSR marker technology was used to identify markerslinked to CMD resistance via bulk segregant analysis (BSA).One hundred and fortymolecular markers from the International Center for Tropical Agriculture (CIAT) were usedto screen the parents, contrasting bulks and the individuals that make up the contrasting bulks.The bulk segregant analysis produced forty polymorphic markers. Screening of thecontrasting individuals with the polymorphic markers revealed four candidate markers (SSRY238, SSRY 51, SSRY 76 and SSRY 20) linked to CMD resistance. The correlation coefficientvalues between genotypic and phenotypic data classes for candidate markers were generallylow. The t-test value between both genotypic classes (absence of band versus presence ofband) were not significant (P>0.05) in each of the four markers. The results from this studysuggest that there are at least two new CMD resistance genes in the mapping population.