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Articles by R.D. Narla
Total Records ( 4 ) for R.D. Narla
  J.W. Kimenju , G.O.M. Odero , E.W. Mutitu , P.M. Wachira , R.D. Narla and W.M. Muiru
  This study aimed at evaluating the suitability of selected substrates for mushroom production. Ten different substrates namely water hyacinth (Eichhornia crassipes), maize cobs (Zea mays), coconut fibre (Cocos nucifera), finger millet straw (Seteria microcheata), banana fibre (Musa sp.), sawdust (Eucalyptus sp.), rice straw (Oryza sativa) bean straw (Phaseolus vulgaris) and wheat straw (Tritichum aestivum) were tested for their suitability in mushroom production. Plastic bags were filled with 250 g of substrate and arranged in a randomized complete block design. The substrates had a significant (p≤0.05) effect on days to pinning, number of caps and biological efficiency. Compared to the control, which pinned at 28 days, maize cobs, sawdust and coconut fiber had short pinning durations of 19, 22 and 23 days, respectively. With the exception of sawdust, water hyacinth and maize cobs, the rest of the organic substrates significantly increased the marketable caps of the oyster mushroom. The straws, namely, bean, rice, finger millet and wheat had the highest biological efficiency in decreasing order of 106, 92, 85 and 77%, respectively. Stipe length was longest in oyster mushroom grown on bean straw, followed by finger millet straw, maize cobs, banana fiber and shortest in sawdust. Mushroom yield was, 80, 78, 76, 73 and 68%, higher in bean straw, rice straw, millet straw, wheat straw and banana fibre treatment compared to the control. Mushroom yields on sawdust were 60% lower than the control. In descending order of suitability bean, rice, finger millet and wheat straws can be recommended for oyster mushroom production.
  R.D. Narla , J.W. Muthomi , S.M. Gachu , J.H. Nderitu and F.M. Olubayo
  Field experiments were conducted over two growing seasons to determine the effectiveness of vegetable intercrops in the management of downy mildew (Peronospora destrutor) and purple blotch (Alternaria porri) of bulb onion. Vegetable intercrops evaluated, were carrot (Daucus carota), spider plant (Cleome gynandra) and French bean (Phaseolus vulgaris). The efficacy of the vegetable intercrops in reducing the foliar diseases was compared to a fungicide Tata Master™ (metalaxyl8%+mancozeb 64%). Each vegetable was intercropped with three onion varieties (Bombay Red, Red creole and Orient F1) and downy mildew and purple blotch development were determined until physiological maturity. Vegetable and bulb yields were also determined at harvest. The vegetable intercrops significantly reduced downy mildew and purple blotch severity but had no significant effect on disease incidence. Spider plant was the most effective vegetable intercrop in reducing downy mildew severity by up to 21% and purple blotch severity by 18%. Onion varieties Red creole and Bombay red had low disease levels compared to orient F1. Although intercropping onion with vegetables reduced bulb yield, it improved the gross return per unit area. The results showed that intercropping bulb onion with vegetables could be beneficial in reducing foliar diseases and improving gross return per unit area. However, further studies are necessary to determine the optimal spatial arrangements of onion and vegetable intercrops in foliar disease management.
  J.W. Muthomi , G.M. Riungu , J.K. Ndung`u , R.D. Narla , J.K. Gathumbi and J.M. Wagacha
  The study was carried out during the 2006 cropping season in Nakuru district, Kenya. Incidence and severity of head blight were determined and pathogens isolated from diseased wheat heads, wheat and maize kernels. Mycotoxin deoxynivalenol content in grain was determined by direct competitive Enzyme-Linked Immunosorbent Assay (ELISA). Pathogenicity of different Fusarium species isolated from wheat was determined by inoculation onto wheat ears in greenhouse. Head blight was highly prevalent (90-100%) and mean incidence and severity ranged from 4 to 9% and 15 to 37%, respectively. Fusarium was most prevalent in infected wheat heads while Epicoccum was most prevalent in harvested wheat grain. Only Fusarium spp. and Penicillium spp. contaminated harvested maize grain. The most frequently isolated Fusarium species were F. poae, F. graminearum and F. chlamydosporum in wheat and F. verticilloides in maize. Most wheat and maize grain samples were contaminated with mycotoxin (DON), with concentration ranging from 0-1,200 and 0-4,600 µg kg-1, respectively. Fusarium graminearum isolates were highly pathogenic, significantly reducing kernel weight. The results suggest that head blight in Nakuru district is due to a complex of Fusarium species with F. graminearum being the major pathogen. Cross-contamination of wheat and maize is implied, indicating possible contamination of wheat maize products with deoxynivalenol mycotoxin.
  G.M. Riungu , J.W. Muthomi , R.D. Narla , J.M. Wagacha and J.K. Gathumbi
  Laboratory and green house studies were conducted at the Faculty of Agriculture, University of Nairobi, to evaluate the efficacy of Epicoccum sp., Alternaria sp., Trichoderma sp. and Bacillus sp. in control of Fusarium head blight of wheat caused by F. graminearum. Fungicides folicur® and copper oxychloride were used as standard checks. Laboratory assay was carried out by paired cultures and antagonism was measured as reduction in pathogen colony diameter. Green house experiments involved dual inoculation of pathogen and antagonist onto wheat ears and head blight severity and grain yield determined. Doxynivalenol content in the resulting grain was determined by competitive direct ELISA. The antagonists and fungicides significantly reduced the growth of Fusarium graminearum colonies in culture. Folicur® and copper oxychloride completely inhibited the growth of the pathogen while Trichoderma sp. showed 64% colony growth reduction. However, the antagonists showed limited reduction in head blight severity in green house trials. Trichoderma sp. reduced head blight severity by 18% while folicur® reduced the disease by 28%. All the antagonists had little or no significant effect on grain yield. Only folicur®, copper oxychloride and Alternaria sp. reduced DON in grain by 76 to 93%. Obtained results indicate that microbial antagonists may offer potential benefit in FHB management and screening of more antagonists both under controlled and field conditions is necessary.
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