Browsing by Author "Haukeland, S."
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Item Biocontrol Potential of Four Indigenous Entomopathogenic Nematodes From Kenya(Canadian Center of Science and Education, 2021-09-15) Ngugi, C.N.; Wachira, P.M.; Mbaka, J.N.; Okoth, S.; Haukeland, S.; Thuranira, E.G.; Kenya Agricultural and Livestock Research Organisation ; University of Nairobi ; International Center of Insect Physiology and EcologyGlobally, vegetable production including tomato is constrained by pests and diseases. The tomato leafminer, Tuta absoluta (Meyrick.), is a major pest of tomato, mainly managed using chemical pesticides. There is a need for integrated pest management (IPM), approaches that are human and environmentally friendly. The study aimed at molecular identification and virulence evaluation of four entomopathogenic nematodes (EPNs) against T. absoluta larvae. The DNA was extracted, sequenced, and phylogeny analyzed. The EPNs virulence was evaluated using the insect baiting technique at different nematode concentrations (0-Control, 100, 150, 200, and 250 infective juveniles/ml of distilled water). Larval mortality data were collected for five days. Molecular identification resulted in nucleotide sequence lengths of 877-895 base pairs (bp). All the isolates were found to be Steinernema species of EPNs. The % similarity of the isolates and their close relatives ranged between 82-100%. The isolates closely matched Steinernema spp. AY230184 (Sri Lanka); AY230186 (Kenya), JN651414 (Ethiopia), and MW151701 (Kenya). The sequences were deposited to Genbank as Steinernema sp. Isolate Kalro 75 (MW150871), Steinernema sp. Isolate Kalro S86 (MW150872), Steinernema sp. isolate Kalro97 (MW150873) and Steinernema sp. Isolate KalroR52 (MW150874). All the EPN isolates were virulent against T. absoluta. Isolate Kalro R52 and Kalro S86 recorded the highest mortality of 76±7.5%; 72±15.0% respectively in the 48 h. There was a significant difference (P < 0.001), between all the isolates and the Control. The four EPNs were virulent and have bio-control potential against, T. absoluta. Research on their virulence against T. absoluta in the field is recommended.Item Characterization and Pathogenicity Test of Entomopathogenic Nematode Steinernema Species-Kalro(Canadian Center of Science and Education, 2021-02-15) Ngugi, C.N.; Wachira, P.M.; Mbaka, J.N.; Okoth, S.; Haukeland, S.; Mburu, H.M.; Adhiambo, M.; Sirengo, D.K.; Kenya Agricultural and Livestock Research Organisation ; University of Nairobi ; International Center of Insect Physiology and EcologyEntomopathogenic nematodes (EPNs) are worldwide soil-dwelling insect parasitic nematodes. They are potential pest bio-control agents a key component of Integrated Pest Management (IPM) programs. This study aimed to characterize and evaluate the pathogenicity of an EPN isolate from Kenya. The nematode was isolated from soils using insect bait technique and both morphological and molecular identification was performed. Efficacy of the isolate was evaluated against Tomato leafminer larvae (Tuta absoluta Meyrick.) using dose-based treatments of 0-control, 100, 150, 200, and 250 infective juveniles (IJs/ml). Morphological analysis revealed body length (L) of 835(659-987) µm and 1781 (1297-2097) µm from fresh IJs and males respectively. Males lacked a mucron. The isolate was characterized by the partial sequence length of 877 bp of the ITS region. Blastn results indicated the EPN isolate had a similarity match of 81-92% with Afro-tropical Steinernema species. It matched with Steinernema sp. (AY230186.1) from Kenya at 92% and Sri Lanka (AY230184.1). Phylogenetic analysis placed the isolate together with Steinernema sp. (AY230186.1) and (AY230184.1) with a bootstrap value of 100%. Maximum mean larval mortality (80%; 96%) was achieved 24 and 48 h post-treatment at concentration 150 IJs/ml. All nematode concentrations achieved over 50% mean mortality after 24 h period. There was a significant difference (P = 0.001) between doses 150 and 200 IJs/ml. From the study, it was concluded that the nematode isolate was Steinernema sp now referred to as Steinernema sp. Kalro (Genebank Accession MW151701). The EPN has the potential for development as a biological control agent against T. absoluta.Item Relative Yield Loss of Potato in Fields Infested with Potato Cyst Nematodes and the Efficacy of Selected Control Products in Nyandarua County, Kenya(East African Agricultural and Forestry Journal, 2022-12-15) Mbiyu, M.W.; Kimenju, J.W.; Muiru, W.M.; Nyongesa, M.W.; Haukeland, S.; University of Nairobi ; Kenya Agricultural Livestock Research Organization ; International Centre of Insect Physiology and Ecology (icipe) ; The Norwegian Institute of Bioeconomy Research (NIBIO)Despite the rapid spread of potato cyst nematodes (PCN) in Kenya, data on associated yield loss is limited. The objective of this study was to determine the efficacy of four nematicides and relative yield loss associated with PCN damage. Three on-farm sites with varying PCN densities (low; 1-9, moderate; 10-39, and high; 40-80 cysts in 100 g/soil) were selected for the study in Nyandarua County during the 2021 long and short rains seasons. Treatments consisted of three potato cultivars namely Desiree and Shangi (susceptible) and Manitou, which is partially resistant. The four PCN control products tested were, fluopyram, oxamyl, azandirachtin (commercial neem extract) and Paecilomyces lilacinus. The experiments were set up in a randomized complete block design, in a split plot arrangement, with varieties as the main plots, and PCN control products including the control as the sub-plots. Treatments were replicated three times. The reproductive index of the nematodes ranged from 0.17 to 2.39 during the long rains and from 0 to 4.13 during the short rains season. Relative yield loss attributed to PCN infection varied from 6.3% to 80.5% during the long rain season and from 5.5% to 73.3% during the short rain season. The magnitude of yield losses was dependent on susceptibility of the variety and the initial PCN population density. This study has demonstrated that PCN are already causing substantial yield losses especially in heavily and moderately infested fields. The study demonstrated that oxamyl was the most effective nematicide in reducing PCN numbers and yield losses. Farmers are advised to take appropriate measures to prevent spread and buildup of the nematodes.
