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Articles by G.K. Mutua
Total Records ( 6 ) for G.K. Mutua
  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
  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. Kimenju , A.M. Kagundu , J.H. Nderitu , F. Mambala , G.K. Mutua and G.M. Kariuki
  Green manure plants were evaluated to determine their suitability as rotation crops with common bean to suppress root-knot (Meloidogyne spp.) nematodes. They were also evaluated as soil amendments in nematode control. The plants were Calliandra calothyrsus, Canavalia ensiformis, Chenopodium quinoa, Crotalaria juncea, Desmodium uncinatum, Gliricidia sepium, Leucaena leucocephala, Mucuna pruriens, Tephrosia purpurea, Tithonia diversifolia, Vicia villosa, Sesbania sesban and Tagetes minuta. In the glasshouse, pots were filled with steam-sterilized soil and sown with green manure plants. The rotation experiment entailed growing green manure plants for three months before uprooting them and planting beans in the same pots. The potting medium was infested with 6000 eggs/juveniles of Meloidogyne javanica. The field experiments were carried out in microplots infested with a mixture of M. javanica and M. incognita. Damage to bean roots due to root-knot nematodes was based on galling indices while nematode reproductive potential was based on egg mass index. Tithonia diversifolia, D. uncinatum, T. minuta, L. leucocephala and C. juncea were among the most effective in root-knot nematode suppression when used in rotation with beans. Their galling indices ranged between 1.0 and 1.5 under field conditions and were thus considered resistant. Vicia vilosa, T. purpurea and S. sesban were susceptible with galling indices ranging between 6.2 and 7.7. The resistant plants reduced the reproductive potential of Meloidogyne spp. by up to 80% while the susceptible plants caused an increase of up to 600%. Therefore, T. diversifolia, D. uncinartum, T. minuta, L. leucocephala and C. juncea can be recommended for use in fields infested with root-knot nematodes.
  A.N. Mweke , J.W. Kimenju , A.A. Seif , E.W. Mutitu and G.K. Mutua
  The response of different crops to a mixed population of root-knot nematodes, Meloidogyne javanica and M. incognita and their potential as suppressants in sequential cropping systems was evaluated in greenhouse and field experiments. Crops rated as resistant were five maize cultivars, four sorghum cultivars, two millet varieties, guwar and two pigeonpea cultivars which had galling indices ranging between 1.4-3.6. cowpea cv. K80 was rated as moderately resistant with a galling index of 4 while greengram and cowpea cv. KKI were rated as susceptible with galling indices ranging from 5.6 to 7.4. Four crops namely sweetcorn, babycorn, maize cv. Pioneer (Ph3253) and guwar were selected after the greenhouse tests for field trials, based on their poor host status to root-knot nematodes as well as relative acceptability to vegetable growers. These crops were then incorporated into a rotation program with okra. Initial and final J2 numbers in the field were determined before planting and at the end of the season, respectively. Okra was then sown in the plots previously grown with the selected nematode suppressive crops and the nematode numbers determined mid and end of the season. A 44 and 21% decline in nematode numbers was recorded in plots under guwar or sweetcorn and babycorn, respectively. In contrast, a 441% increase in nematode numbers was recorded in plots under continuous crop of okra. The galling index on a crop of okra that followed sweetcorn was 3.3 compared to 8.6 in the control which was continuously under okra, resulting in an increase in yield within a range of 60-92%. This underscores the potential of rotating highly susceptible crops with poor hosts in the management of root-knot nematodes.
  J.K. Langat , J.W. Kimenju , G.K. Mutua , W.M. Muiru and W. Otieno
  This study was carried out with the aim of evaluating the effect of ecologically sound approaches for nematode management on non-target organisms, free-living nematodes. The materials tested were sugarcane bagasse, molasses, tea and flower composts, neem (Achook), a biological agent (Paecilomyces lilacinus) and fenamiphos (Nemacur). The treatments were administered before planting carnation var. White Natila in flower beds that were naturally infested with nematodes. Application of bagasse, molasses, tea and flower composts resulted in increased abundance of free-living nematodes compared to the control where nothing was applied. Bacterial feeders, fungal feeders, and predators comprised 73, 14 and 13%, respectively of the free-living nematodes recovered. Members of the genus Rhabditis were the most abundant (10%) among the bacteriovores while Mononchus (10%) and Aphelenchoides (14%) dominated among the predators and fungivorous trophic groups, respectively. The highest numbers of free-living nematodes were recorded at 90 Days after Planting (DAP) in plots treated with bagasse and molasses but the numbers declined at 180 DAP. A steady increase in numbers of free-living nematodes was observed in plots treated with tea and flower composts up to 180 DAP. Significant reductions in abundance of free-living nematodes were recorded in plots treated with fenamiphos and neem. This study has established that application of organic substrates serve as a stimulus to processes leading to build-up of free-living nematodes. The organic substrates can strongly be recommended for use in sustainable carnation production systems.
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