Phenotypic and molecular characterization of released and elite sweetpotato varieties in Ghana compared with virus-tested putative ramets

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Following release of Ghanaian sweetpotato varieties which are selections from exotic introductions, no effort was made to maintain true-to-type virus-tested foundation seed stocks. Original exotic virus-tested plants of Ghanaian released and elite varieties obtained from CIP were introduced and compared with putative ramets using morphological descriptors and molecular markers, yield and quality attributes and severity of virus symptoms with time. Planting materials of cultivars and introduced virus-tested materials of same genotypes were field multiplied at Fumesua, Ghana, before planting in replicated trials at two locations during the 2011 major growing season. Standard morphological descriptors and molecular markers were used to assess similarity of genotypes, while yield and virus symptoms during growth were used to determine benefits of using virus-tested planting material. The Ghanaian released varieties Otoo and Sauti were found to be closely related with original source material. Conversely, Faara and Okumkom were found not to be closely related with original source material. The recently introduced virus-tested genotypes, Mogamba and Kenya, yielded significantly (p < 0.05) higher than putative ramets and could be used as a source of clean planting material. On the contrary, TIS 3017 and TIS 8266 also introduced recently, produced significantly (p < 0.05) lower yields than putative ramets. These varieties should be cleaned locally using in vitro tissue culture techniques. Mogamba was found to be the genotype with the lowest expression of virus symptoms and recorded the highest yield. More attention should be given to maintenance of seed quality of virus-free stocks and continuous selection for trueness to type.
A Thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the Degree of Master of Science in Agronomy(Plant Breeding), August-2012