Genetic transformation of sweet potato[ipomoea batatas(L.) lam] with nicotiana protein kinase 1 gene to enhance drought stress tolerance
Sweet potato [Ipomoea batatas (L.) Lam] is a valuable source of food and 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. However in Africa sweet potato yields are very low. The area under sweet potato in Africa is approximately 1,714,000 hectares with an annual production of about 5.5 million tons. Drought stress is one of the most significant abiotic constraints to sweet potato production in sub Saharan Africa. The application of biotechnology tools like genetic engineering for the improvement of important crop plants has been shown to have great potential. The objective of the study described herein was to genetically transform selected sweet potato cultivars with a tobacco Nicotiana Protein Kinase 1 gene which has been shown to confer drought stress tolerance in transgennc maize, yeast and Arabidopsis thaliana. Four orange-fleshed sweet potato cultivars namely KSP36, Ukerewe, Mayai and Carrot were used in this study. It was possible to regenerate plants from KSP36 and Ukerewe cultivars on three concentrations (0.5, 1.0 and 1.5 mg/L) of Indole-3 acetic acid (IAA) with average regeneration efficiencies of 8.3% and 6.2%, respectively. The concentration of 1.0 mg/L IAA was found to be the best (P<0.002) for regeneration of Ukerewe and KSP36 sweet potato cultivars. The study also established that the use of leaf or stem as explant had no significant (P<0.219) effect on regeneration efficiency of the tested cultivars. However it was confirmed (P<0.001) that regeneration efficiency is genotype-dependent in sweet potato since plant regeneration was only achieved in two of the four tested cultivars. The Agrobacterium tumefaciens strain EHA101 harbouring the binary vector plasmid pSHX004 with the NPKI transgene and bar selectable marker gene was used for genetic transformation of Ukerewe and KSP36 sweet potato cultivars. Putatively transformed callus and plantlets were screened by including 0.5 mg/L bialaphos in sweet potato culture media. Putative transformation efficiencies of 1.04% and 1.59% were achieved for KSP36 and Ukerewe, respectively. The putatively transformed sweet potato produced in.this study need to undergo drought stress tolerance assays and RT-PCR to assess expression of NPKI gene and actual drought stress tolerance. The regeneration efficiency was a very important factor influencing transformation efficiency. The findings of this study could provide new opportunities for producing drought stress tolerant sweet potato for sub Saharan Africa using genetic engineering.