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Articles by J.P. Ouma
Total Records ( 5 ) for J.P. Ouma
  R.C. Ramkat , A.W. Wangai , J.P. Ouma , P.N. Rapando and D.K. Lelgut
  Tomato (Lycopersicon esculentum) is popular both in fresh market and processing industries. Tomato yields are limited by diseases, Tomato spotted wilt tospovirus (TSWV) disease being one of them. A study was conducted in a greenhouse to determine the effect of mechanical inoculation of tomato spotted wilt tospovirus on the severity of the disease on tomato varieties Cal J, Marglobe, Money maker, Roma and Riogrande and its impact on yield. The experiment was arranged in a split plot design replicated four times. Tomatoes variety Cal J was most severely affected by the disease whereas Marglobe and Riogrande were least affected. Mechanical inoculation reduced total yield of Cal J, Riogrande, Money maker, Marglobe and Roma by 60, 55.3, 45.1, 40.3 and 27%, respectively. Marketable yield was reduced significantly by inoculation for the varieties except for Roma with a slight reduction in marketable yield that was not statistically significant from healthy controls. Roma was shown to be a tolerant variety that can be given to resource poor farmers as a component of an Integrated Pest Management (IPM) system for control of TSWV in order to realize higher marketable yields.
  J.N. Oggema , M.G. Kinyua and J.P. Ouma
  Embryogeneic callus induction and subsequent differentiation is accomplished by application of suitable growth regulators and controlling conditions during culture. The growth regulator, 2,4-D is one of the most effective auxin for calli induction in sweet potato (Ipomoea batatas (L.) Lam.), however the optimum concentration varies with individual cultivars. The optimum 2,4-D level for the local sweet potato cultivars has not been determined yet it is important in multiplication of planting material and transformation procedures. To determine the optimum 2,4-D concentration that produced embryogenic calli early and in high frequencies for local Kenyan sweet potato cultivars Mugande, SPK004, Kemb10, Japon tresmesino and Zapallo, leaf explants were cultured in vitro on MS basal medium supplemented with six concentrations of 2,4-D (0, 0.5, 1.0, 2.0, 3.0 and 5.0 mg L-1), set as a factorial treatment arranged in a Completely Randomized Design (CRD), replicated three times. For each treatment four parameters were considered: Mean number of days taken to form calli, calli weight, calli diameter and calli strength. The results established significant (p<0.05) differences in cultivar responses to 2,4-D levels. Calli induction was effective when supplemented at low levels of 0.5 mg L-1 as high levels above 3.0 significantly reduced the quantity and quality of embryogenic calli that was formed. Low levels of 2,4-D should be used for local Kenyan sweet potato cultivars as the number of days taken to form calli reduced and calli incidences increased.
  J.N. Oggema , J.P. Ouma and M.G. Kinyua
  The development of a reliable plant regeneration protocol in sweet potato forms the basis for sweet potato (I. batatas) genetic improvement. The success in production of the transgenic sweet potato is dependent on the reliability and efficiency of the regeneration protocol to produce somatic embryos capable of forming whole plants. The effect of direct and indirect embryogenesis on in vitro plant regeneration was studied and thereafter a suitable tissue culture protocol for 5 locally adapted Kenyan sweet potato cultivars Mugande, SPK004, Kemb10, Japon tresmesino and Zapallo established. Embryogenic calli was induced directly and indirectly from sweet potato leaf explants and auxiliary buds cultured on MS medium supplemented with 2,4-D (0, 0.5 and 1.0 mg L-1). Absisic acid was added to induce embryo maturation and when the hormone levels were reduced these embryos began to differentiate into shoots before whole plants were regenerated. For each treatment the number and days taken to form shoots, roots and plants that were regenerated were counted and used as a selection index of an efficient sweet potato regeneration protocol for the locally adaptable Kenyan cultivars. The test cultivar had a significant (p≤0.05) effect on both direct and indirect embryogenesis. The use of indirect embryogenesis was beneficial for the local Kenyan sweet potato cultivars as more calli formed hence ensuring higher plant regeneration and increased mass propagation of in vitro plants while direct embryogenesis took a shorter time to form shoots and roots but fewer plants were regenerated.
  G.B. Ashiono , W. Wasike , J.P. Ouma , S.W. Gatwiku and P.N. Gachuki
  An experiment was conducted over three years to determine the residual effects of different rates of farmyard manure on growth and yield of cold tolerant sorghum variety E1291. The trial was conducted on a sandy loam soil at the KARI-Lanet Research Centre. The manure levels were: 0, 5, 10, 15, 20, 30, 40 Mg ha-1 and inorganic fertilizer at the rate of 60 kg N and 30 kg P2O5 ha-1 applied in the first year. Grain yield increased up to 20 Mg ha-1 farmyard manure beyond which a decline was observed whereas, stover yield increased up to 30 Mg ha-1. Residual farmyard manure consistently produced better yields than inorganic fertilizer. Grain yield increases over inorganic fertilizer ranged from 7.2 to 12.6% and those for stover were 2.3 to 8.4%. Plant population increased by 0.8 to 11.3% and harvestable heads increased from 2.6 to 20%. These results have demonstrated that high and consistent yields may be produced from residual farmyard manure for three consecutive seasons after the initial application.
  G.B. Ashiono , J.P. Ouma and S.W. Gatwiku
  An experiment was conducted over three seasons to determine the effects of different rates of application of Farmyard manure and inorganic fertilizer on growth and yield of cold tolerant sorghum variety E1291. The trial was conducted on a sandy loam soil at the Kenya Agricultural Research Institute-Lanet, Kenya. Farmyard manure obtained from the centre cattle shed was incorporated into the soil at the time of sowing at 0, 5, 10, 15, 20, 30 and 40 Mg ha-1 in a Randomized Complete Block Design replicated three times. Standard inorganic fertilizer was included as a control at the rate of 60 kg N ha-1 and 30 kg P2O5 ha-1. The highest grain yield was produced where 5 Mg ha-1 of farm yard manure was applied during the first year while 40 Mg ha-1 produced lowest yield among manure treatments. During the second year significantly (p<0.05) higher grain yields were achieved from treatments of 30 and 40 Mg ha-1. In the third year, no significant differences (p<0.05) were observed among the manure treatments but 30 and 40 Mg ha-1 farm yard manure produced highest yields. Manures produced higher yields in all years than the recommended inorganic fertilizer. After three seasons of evaluation, 10 Mg ha-1 of farm yard manure produced similar grain yields to the standard control while 30 and 40 Mg ha-1 farm yard manure consistently produced highest yields. These yield differences were not significantly different from treatments with 15 Mg ha-1 of farm yard manure.
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