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Articles by F.M. Olubayo
Total Records ( 7 ) for F.M. Olubayo
  A.K. Chirchir , J.W. Kimenju , F.M. Olubayo and G.K. Mutua
  A study was conducted to determine the factors influencing plant-parasitic nematode occurrence, abundance and distribution in the sugarcane fields. Four sugarcane growing zones; Nzoia, Mumias, West Kenya and Busia of Kenya were selected from which 81 fields randomly selected and sampled. Soil samples were taken from sugarcane rhizospheres and nematodes extracted from 200 cm3 soil using the modified Baermann funnel technique. Nematodes were then fixed and mounted on slides and identified to genera level using identification keys. Nematodes of the genera Pratylenchus, Scutellonema and Meloidogyne were predominant in the sugarcane belt of western Kenya with mean densities of 61, 54 and 39, respectively. Nzoia, which falls in a marginal sugarcane zone harboured the highest proportion of these plant parasitic nematodes (55%), while West Kenya zone had the least proportion (4%). Soil texture influenced nematodes with more than 50% occurring in sandy soils compared to other soil types. Build-up of plant parasitic nematodes occurred with subsequent ratoon crops up to the second ratoon before declining in the third ratoon. Anthropogenic effects were significant with 70% higher numbers of plant parasitic nematodes in the out-grower farms compared to the factory-managed farms. This study has revealed the influence of soil texture, crop cycle and anthropogenic factors on abundance and distribution of plant parasitic nematodes in western Kenya sugarcane zones. It has also set the justification of further work to determine the economic importance of the nematodes.
  A.K. Chirchir , J.W. Kimenju , F.M. Olubayo and G.K. Mutua
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  J.O. Nyasani , J.W. Kimenju , F.M. Olubayo , S.I. Shibairo and G.K. Mutua
  This study was aimed at determining the occurrence of entomopathogenic nematodes (EPNs) in different agroecosystems and their potential as biocontrol agents in the management of DBM. Soil samples were taken from a planted forest, pasture, a coffee field and a vegetable garden. EPNs were isolated from the soil using Galleria mellonella as the bait insect. Laboratory bioassays were conducted to determine the lethal time fifty (LT50), which is time till 50% lethality, of the EPN isolates to DBM larvae using the leaf disc bioassay method. Five isolates of EPNs namely Heterorhabditis indica, Steinernema karii, Steinernema wesieri, Steinernema sp. and Heterorhabditis sp. were used. The frequency of occurrence of EPNs was lowest, 27%, in the soil from vegetable garden, followed by forest soil, 33%. EPNs were present in 50 and 77% of the soil samples from pasture and coffee ecosystems, respectively. The LT50 of S. karii, H. indica and S. wesieri was 38.10, 20.27 and 23.80 h, respectively. Heterorhabditis indica, S. karii, S. wesieri, Steinernema sp. and Heterorhabditis sp. caused 96.0, 93.3, 92.0, 88.0 and 86.7% mortality in the DBM larvae within 72 h, respectively. This study has demonstrated that the frequency of occurrence of EPNs is different in various agroecosystems. The study has also showed that EPNs have a great potential that may be exploited along with other suitable strategies in integrated management of DBM.
  J.W. Muthomi , J.N. Nyaga , F.M. Olubayo , J.H. Nderitu , J.N. Kabira , S.M. Kiretai , J.A. Aura and M. Wakahiu
  Field studies were carried out in farmer-based seed potato production to determine the incidence of potato aphids and potato aphid-transmitted viruses in two potato-producing areas of Kenya. Parameters determined included aphid population, virus disease incidence and tuber yield. Aphid population was monitored on leaves and in water-pan traps. Virus infection was determined based on symptoms and the viruses were identified in tubers sprouts by DAS-ELISA. Tuber yield was determined for plants showing virus symptoms and healthy-looking plants. Five aphid species were identified, with the most abundant being M. euphorbiae and A. gossypii on leaves and M. persicae and A. gossypii in water traps. The average aphid population was between 1.4 and 4.2 aphids per three leaves and 4.68 and 9.64 aphids per water pan trap. Farms with higher population of M. persicae had higher virus disease incidence. The most prevalent viruses were PVS, PLRV and PVM. Healthy looking plants had a latent infection rate 57.2% compared to 76.6% for symptomatic plants. Virus infection reduced the number and weight of tubers by 74 and 62.7%, respectively. However, virus infection increased the number and weight of the chats grade. The results indicated that aphid infestation and virus disease incidence were higher than the recommended for seed potato production. Therefore, there is need to create awareness among the farmers on aphid and virus symptom recognition and use of clean certified seed potato.
  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.
  A.W. Mwang`Ombe , G. Thiong`O , F.M. Olubayo and E.K. Kiprop
  Seven hundred and fifty bean plant samples with root rot symptoms were collected from farmers' fields during two surreys carried out in Embu district, Kenya. Various fungal pathogens were isolated in the laboratory from these samples; among them were 50 isolates of Rhizoctonia solani, which were subjected to pathogenicity tests in a glasshouse. Thirty-six isolates of R. solani obtained from beans with root rots were subjected to DNA microsatellite analysis. Five isolates of R. solani that cause black scarf of potatoes (Solanum tuberosum L.) were also analysed alongside those from the beans. A total of 50 alleles were detected when six microsatellite loci were typed in the 41 samples, with the mean of 8.33 and a range of 3 at locus RB23 to 19 at locus AF513014. The smallest allele size was 129 basepair at locus RE102 and the largest was 297 basepair at locus AY212027. Microsatellite analysis showed a moderate variation among the isolates from different agro-ecological zones and administrative boundaries (divisions). Phylogenetic analysis revealed 3 major clusters within the population of 41 isolates of R. solani from Kenya. Clusters 1, 2 and 3 had 15, 10 and 75% isolates, respectively. However, cluster 3 had 4 sub-clusters and cluster 1 had 2 sub-clusters, while cluster 2 did not have a sub-cluster. There was no relationship between microsatellites and geographical origin of the isolates. This is the first study on the genetic diversity of R. solani using DNA microsatellite analysis in Kenya.
  A.W. Mwang`ombe , G. Thiong`o , F.M. Olubayo and E.K. Kiprop
  Two surveys were carried out in October 2001 (season 1) and April 2002 (season 2) in five divisions of Embu district during the short and long rains, respectively. Ten farms were randomly selected per division and fifteen bean plants were sampled from every farm and used to determine the occurrence and incidence of bean root rot and bean stem maggot. Each bean root was examined for the presence of bean stem maggot and root rot pathogen. The incidences of bean root rot diseases and bean stem maggot were significantly (p = 0.05) higher during the short rain than during the long rains. Wetter agro-ecological zones such as LH2 and UM1 had more incidence of root rot than UM2, UM3 and UM4. During both seasons Fusarium solani, Rhizoctonia solani and Macrophomina phaseolina were the major root rot pathogens isolated. The species of bean stem maggot found in Embu district were Ophyiomia spencerella and O. phaseoli, with the latter being the dominant species. Agro-ecological zones had no significant effect on the incidence of bean stem maggot. Root rot disease was frequently associated with bean stem maggot. Pearson correlation (r) between bean root rot disease and bean stem maggot was 0.495. The result is important in the management of bean root rot and bean stem maggot.
 
 
 
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