The potential of Agrobacterium-mediated transformation of farmer preferred sweet potato genotypes in Kenya
Njiru, Joshua Mugendi
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Sweet potato [Ipomoea batatas (L.) Lam] is a valuable source of food and a source of industrial raw material; its tubers provide high levels of starch, lysine, vitamin A and ascorbic acid. Globally, sweet potato is one of the highest yielding crops with a yield potential of 30 tons/ha. The sweet potato is grown in more than 100 countries. It is already. the seventh most produced food crop in the world surpassed only by wheat, rice, maize, Irish potato, barley and cassava. Approximately 95% of the world annual output is produced in developing countries, in Asia and sub-Saharan Africa. However in Africa sweet potato yields are very low due to abiotic (drought, salinity and temperatures) and biotic factors. In Kenya, sweet potato production does not meet the demand and there is need to increase production both in terms of hectareage and yields. In addition, farmers suffer significant yield loss and the yield levels are 20% of the crops potential (30 tons/ha). Sweet potato biology presents many challenges to conventional breeding through sexual hybridisation. High pollen sterility, sexual incompatibility and the hexaploid nature of sweet potato have resulted in very limited improvement of this important root crop by conventional breeding methods. Genetic engineering can be used to compliment conventional breeding strategies as it is faster and fairly more accurate in transferring target genes. The objective of this study was to genetically transform Kenyan farmer preferred sweet potato genotypes. The Agrobacterium tumefaciens strain EHAIOI harboring the RNAi with a bar selectable marker gene and Agrobacterium tumefaciens strain EHAlOI harboring a GUS reporter gene were used to transform sweet potato using Monsanto sweet potato transformation protocol. Bialaphos (0.5 mg/L) was use to identify transgenic plants. Five sweet potato varieties were used in this research; Mugande, Spk 004, Spk 013, Ksp 36 and Enaironi. All the tested genotypes were able to induce callus from the stem and leaf explants used and transient gene expression was observed to be positive from all the genotypes. Under selection pressure (0.5 mg/L bialaphos) Mugande had the highest transformation frequency of 62.8% from the leaf explants and 40.8% from the stem explants while Enaironi had the lowest having 17.2% from the leaf explants and 6.4% from the stem explants. Out of the five genotypes tested in this research 3 genotypes were able to regenerate transgenic plantlets. Mugande had 4 transgenic plantlets, Spk 004 had 1 and Spk 013 had 1 plantlet. Confirmation of transformation for bialaphos surviving plantlets was done using polymerase chain reaction (PCR). The results from this study provide new opportunities for improving the yield of sweet potato via genetic engineering.