CW-Department of Biochemistry and Biotechnology
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Browsing CW-Department of Biochemistry and Biotechnology by Author "Gichuki, S. T."
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Item Effect of 2, 4-d levels on callus induction of leaf and stem explants of 5 local farmer-preferred sweet potato varieties in Kenya(2010) Machuka, Jesse; Bett, B.; Gichuki, S. T.; Ateka, E.Five local and popular sweet potato (Ipomoea batatas(Lam.) varieties were selected from the major sweet potato growing areas, based on farmer-preferences and desirable characteristics. Both leaf and stem explants were incubated for callus induction with various concentrations of an auxin 2,4 Dichlorophenoxyacetic acid (2,4-D) at 0, 0.5, 1.0, 2.0, and 5.0 mg/L. The highest percentage of callus induction was realized at 2.0 mg/L and 5.0 mg/L 2,4-D in all varieties for both leaf and stem explants. Callus was induced at 3 weeks after incubation of leaf and stem explants in all tested varieties. Stem explants demonstrated a better response to callus induction at all 2,4-D concentrations and in all varieties as compared to leaf explants. All varieties responded differently to callus induction.Item Interaction of cassava mosaic disease and cassava brown streak disease in nicotiana benthamiana(2010) Ngeranwa, J.J.N.; Irungu, J.; Miano; Mbogo, E.; Monjero, K.; Gichuki, S. T.The interaction of Cassava mosaic geminivirus (CMG)and Cassava brown streak virus (CBSV) were tested in Nicotiana benthamiana. The inoculated virus and/or virus species were CMGs species (ACMV and EACMV-UgV), CBSV and dual CMGs and CBSV. The inoculum source was N. benthamianaplants pre-infected with viruses from diseased cassava cultivars collected from the western region of Kenya. Leaf samples from virus-infected N. benthamiana plants were ground in inoculation buffer [0.1M K-phosphate buffer, pH 7.0, containing 0.01% (w/v) βME and Na2SO3]. The leaf homogenates were rubbed on 2-3 carborundum-dusted leaves of Nicotiana benthamiana plants at 3-5 leaf stage. Four treatments, CMGs (UgV+ACMV); CBSV; combination of CMGs+CBSV and non inoculated control plants were applied with 10 plants per each treatment inoculated in two trials. The plants were grown in a screen house and data recorded on severity of symptoms on leaves, days to symptom appearance and the percentage of infected plants. Highly significant p<0.05 difference were observed on the severity of the disease but differences in days to first appearance of symptoms and the number of infected plants were not significant p<0.05. The most severe symptoms of the disease and number of infected plants were observed in plants infected with both CMGs and CBSV (4.7 and 8) respectively. The earliest symptoms appeared in plants infected with CBSV (5 dpi) and dual infection took the longest period before symptoms were observed (9dpi). None of the plants in the control exhibited leaf symptoms. The dually infected plants exhibited more severe symptoms compared to single infections indicating synergistic interaction when the two viruses occur in combinationItem Optimisation of parameters for agrobacterium-mediated transformation of sweet potato(2010) Machuka, Jesse; Njagi, W.; Gichuki, S. T.; Macharia, C.; Muluvi, G. M.An Agrobacterium-mediated transformation and somatic regeneration protocol was adapted for a Kenyan sweet potato variety, KSP36. A model cultivar, CTP560 was used as a control. For selection of transformed explants paramomycin was found to be effective at 25mg/L while kanamycin was effective at 20mg/L. The lower concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) concentrations proved better for regeneration as opposed to the higher 2,4-D concentrations. Zeatin/ IAA (indole acetic acid) was more effective at embryo production as opposed to kinetin/ 2,4-D medium in both cultivars. Out of the 18 KSP36 plants tested by PCR, 11 tested positive for the coat protein gene while 9 out of the 19 CPT560 plants tested positive. This protocol can be recommended for other sweet potato varieties.