DSpace Repository :: Browsing by Author "Karuri, Hannah W."

Browsing by Author "Karuri, Hannah W."

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Behavioural Patterns and Responses to Human Disturbances of Wild Somali Ostriches (Struthio molybdophanes) in Samburu, Kenya.
(2016-08) Mutiga, Mariciano Iguna; Muoria, Paul Kimata; Kotut, Kiplagat; Karuri, Hannah W.
Somali ostrich has suffered a drastic decline in its population and range mainly due to hunting over the years for meat, skin and feathers. Urgent conservation measures should therefore be taken to reverse this trend particularly in their current population stronghold, the Samburu landscape. In this range, the magnitude and consequences of human disturbance on the ostrich has not been established. The aim of this study was therefore to investigate the behavioural patterns and assess the impacts of human disturbance to the bird. Focal animal sampling was used to establish ostrich‟s behavioural activity budget while the magnitude of human disturbance was assessed by determining and comparing flight initiation distances in the protected and partially protected areas. Somali ostrich spent most of their diurnal time in feeding and moving, and are more sensitive to human disturbance in the protected areas than they are in the partially protected areas. The results of this study imply that the ratite does not differ in behavioural patterns from other extant ostrich species and human disturbance is not posing a significant threat to its survival within Samburu landscape. Further studies are recommended for better understanding of the conservation status of the newly published species.
Food web structure of nematode communities in irrigated rice fields
(Heliyon, 2023-02) Mokuah, Dorcas; Karuri, Hannah W.; Nyaga, Justine M.
Nematodes are a key component of the soil food web and they play an important role in the provision of ecosystem services. Rice cultivation in Mwea, Kenya involves the intensive use of fertilizers and pesticides which may affect the complexity of the nematode-based soil food web. This study examined the nematode diversity and food web structure in irrigated rice fields in Nyangati and Tebere in Mwea, Kirinyaga County, Kenya. Nematodes were identified up to the genus level and soil physico-chemical properties were also determined. Aphelenchoides and Longidorus occurred in significantly greater proportions in Tebere, while in Nyangati there was a high abundance of Helicotylenchus. Aphelenchoides was positively correlated to soil electrical conductivity. From additive diversity partitioning of genus richness, the α and β components contributed 33.7% and 66.3% of the γ diversity, respectively. For Shannon and Simpson diversity indices, the largest contribution to overall diversity was from α component. Soil food web indices were similar across the two regions. Channel and basal indices were below 30% while Enrichment (EI) and Structure (SI) indices were above 50%. There was no variation in metabolic footprints except for the fungivore footprint which was significantly higher in Tebere. Based on the EI and SI, the soil food web in paddy rice fields in Mwea was structured and enriched with moderate disturbance. Due to the high prevalence of economically damaging parasitic nematodes in the rice fields, appropriate management schemes that enhance specific components of the soil food web and increase the suppressive ability of soil against plant-parasitic nematodes should be implemented.
Free-living nematode assemblages associated with maize residues and their ecological significance
(2021) Karuri, Hannah W.; Maina, Samuel; Nyoike, Rossa N.
Return of plant residues to the soil is a sustainable way of enhancing plant growth, health, and levels of soil quality. In Kenya, maize plant residues are the most commonly returned plant material in many agro-ecosystems. For any plant material to release nutrients into the soil, it must undergo a decomposition process that is usually affected by various organisms, especially nematodes. Despite their great contribution to the breakdown of plant organic matter, there is a dearth of information on the interaction between maize residues and free-living nematodes (FLN) in Kenya. In this respect, this study aimed to assess the inﬂuence of decomposing maize residues on FLN dynamics and the soil food web in Mwea, Kenya. The experimental plots were set up in a randomized complete block design, comprising of decomposition plots (incorporated with maize residue to a depth of 30 cm at a rate of 5 tons/hectare), while the plots unincorporated with maize residues were used as the control. Each treatment consisted of four replicates. In all, 30 FLN genera were recovered from the ﬁeld trials, whereby Acrobeles was signiﬁcantly abundant in decomposition plots in both seasons. We subsequently found that maize residues reduced the abundance of enrichment opportunist bacterivores (cp-1) relative to general opportunist (cp-2) bacterivores and fungivores. Notably, the results of the channel index showed that the decomposition of maize residues was dominated by fungal energy channels throughout the study in the two seasons. These results suggest that maize residues need to be coupled with a suitable labile organic matter. This would lead to sustainable, active, and reliable turn-over of maize residues into the soil food web ecosystems. The application of labile materials can also help to improve the population of enrichment bacterivores that are essential in the decomposition process. This study shows that the decomposition of maize residues inﬂuenced FLN composition, mainly the enrichment opportunist bacterivores whose abundance was lower.
Impact of low-cost management techniques on population dynamics of plant-parasitic nematodes in sweet potato
(Elsevier, 2020-07) Maina, Hellen; Karuri, Hannah W.; Rotich, Felix; Nyabuga, Franklin N.
Sweet potato is an important food security crop but its production is limited by various biotic constraints including plant-parasitic nematodes (PPN). In Kenya, current PPN management practices in sweet potato have several limitations hence the need for alternative low-cost management strategies. This study evaluated the impact of intercropping maize and sweet potato (MS) and application of Tithonia diversifolia (MG), cow (CM) and goat manure (GM) on population dynamics of PPN and the effect on metabolic footprints, ecological and functional indices. Field experiments were established in a randomized complete block design involving the four treatments and unamended controls. Soil samples were collected during long (LR) and short (SR) rains seasons. Forty-seven nematode genera were identified in both seasons. Principle response curves analysis revealed that goat manure had the most pronounced effect on PPN. There were differences in metabolic footprints, ecological and functional indices during LR and SR. In CM plots, predator footprint was high during the long rains season. Functional metabolic footprints categorized all plots as degraded in both seasons except MS which was structured in SR. However, CM bordered a structured ecosystem in both seasons while GM bordered a structured ecosystem in LR. Goat manure may have enhanced the natural ability of soil to regulate PPN affecting sweet potato and it may provide an alternative sustainable method of PPN control for smallholders.
Land use effects on termite assemblages in Kenya
(Heliyon, 2021-12) Kanyi, Nahashon Chege; Karuri, Hannah W.; Nyasani, Johnson O.; Mwangi, Benson
Termites perform key ecological functions and they also cause crop damage. Land use change resulting from agricultural intensiﬁcation can result in changes in termite species diversity and abundance. Termite species occurring in natural vegetation, maize monocrop and maize-beans intercrop macrohabitats were investigated in Embu and Machakos Counties, Kenya. Inﬂuence of soil properties and seasons was also evaluated. Across the two Counties, seven termite species were recorded with Machakos County having the highest number. Additive diversity partitioning of species richness and Simpson diversity showed that, α component contributed to 98.3% and 99.1% of the total diversity, respectively. Population densities of three termite species signiﬁcantly varied between land use types in Machakos County but there were no differences in termite species abundance in Embu County. In addition, there were no signiﬁcant differences in species richness between macrohabitats within each County. In Embu, season signiﬁcantly inﬂuenced the abundance of Macrotermes subhyalinus, M. herus, and Coptotermes formosanus which occurred in greater numbers during the wet season. There was a signiﬁcant inﬂuence of land use on Trinervitermes gratiosus and C. formosanus in Machakos with both species occurring in higher numbers in natural vegetation. Trinervitermes gratiosus was negatively associated with Mn and positively correlated to pH and sand. Macrotermes subhyalinus and M. herus showed a positive association with P and silt while C. formosanus was positively correlated to Ca and Mg. These ﬁndings provide an insight into the effects of land use change from natural vegetation to maize agro-ecosystems on termite diversity. It also provides a baseline for further studies on termite diversity in Kenya and their ecological signiﬁcance.
Nematode assemblages, food web indices and metabolic footprints in maize-pigeon pea agro-ecosystems.
(Elsevier, 2022-08) Maina, Samuel; Karuri, Hannah W.; Mugweru, Julius
Pigeon pea (Cajanus cajan L.) and maize (Zea mays L.) are important food crops in developing countries due to their multiple beneﬁts. However, their production is constrained by plant-parasitic nematodes (PPN) which cause signiﬁcant yield losses. Understanding the nematode-based soil food web structure in maize-pigeon pea agroecosystems will allow sustainable PPN management by improving soil health. This study explored nematode community assemblages, indices and metabolic footprints in maize-pigeon pea agroecosystems in Mbeere South, Embu County, Kenya. Soil samples were collected from Gachuriri, Irabari, Kanduu, Kangeta, Kangungi, Kaninwathiga, Karimari and Mutugu regions. The recovered nematodes were identiﬁed to the genus level. There were 41 nematode genera across the eight regions. Longidorus spp., Heterocephalobus spp., Cervidellus spp., Mesorhabditis spp. and Mononchus spp. differed signiﬁcantly across the regions. Meloidogyne spp., Scutellonema spp., Rotylenchulus spp. and Pratylenchus spp. were the most prevalent genera although their abundance was not statistically different across the regions. Using the structure and enrichment indices, soil food web in Irabari was degraded, whereas the other seven regions were structured. The main energy channel of organic matter decomposition in the studied regions was dominated by fungivores. There were no differences in metabolic footprints expect for bacterivore footprint. The occurrence of Hoplolaimus spp. and Xiphinema spp. showed a negative correlation with N, C, Mg and Na. This work provides useful insights into the maize-pigeon pea nematode soil food web structure and function which can be used in improving their yields and soil health.
Nematode diversity and its association with soil properties in monocrop pigeon pea
(Elsevier, 2022-08) Maina, Samuel; Karuri, Hannah W.; Mugweru, Julius
Pigeon pea is a versatile pulse crop grown in semi-arid regions of Kenya; however, its production is affected by plant-parasitic nematodes. The current study was undertaken to investigate the diversity of nematodes and the influence of soil properties on their diversity in monocrop pigeon pea fields in Mbeere North, Embu County, Kenya. Soil samples were collected from Gatunguru B, Gwakaithi, Itururi, Kambungu, Kanyueri, Karigiri, Mbangua and Njarange regions. From each field, soil samples were collected from a depth of 25 cm using W- shaped sampling pattern. The nematodes were identified to the genus level using morphological features. In total, 46 nematode genera assigned to five trophic levels were identified across the eight regions. Abundance of Meloidogyne, Rotylenchulus, Longidorus, Acrobeloides, Cervidellus, Panagrolaimus, Prismatolaimus and Wilsonema varied markedly among the eight regions. Bacterivores belonging to colonizer-persister group 2 were the most prevalent group. There were no differences in Pielou’s evenness, genus richness, Shannon and Simpson diversity indices across the regions. Canonical correspondence analysis indicated significant correlations between certain nematode genera and soil attributes with the first two axes accounting for 56.65% of the variance. Acrobeloides correlated positively with Mg, C, Mn and N, and negatively with Fe. The occurrence of Hoplolaimus and Mesorhabditis was associated negatively with soil pH, clay and Ca, and positively with sand. The present work reveals a high abundance of economically important PPN in monocrop pigeon pea which necessitates that appropriate nematode management programs are implemented.
Nematode metabolic footprints, ecological and functional indices in tropical maize-beans agro-ecosystems under different farming practices
(Elsevier, 2020-10) Maina, Samuel N.; Karuri, Hannah W.; Ng'endo, Rossa N.
Maize and beans contribute significantly to food security in Kenya. Farming practices used in production of these crops may affect nematode community assemblages and influence agricultural productivity. Information on response of nematofauna, particularly free-living nematodes, under various agronomic practices in Kenyan maize-beans intercrop is scarce. This study reports on the effects of farming practices on nematode community dynamics, ecological and functional indices, nematode metabolic footprints, and predator-prey relationship in maize-beans cropping systems in Mwea, Kenya. The field trials were set up in two seasons in a randomized complete block design with each treatment consisting of four replicates. The treatments included cow manure plus chemical fertilizer (CmDCF), cow manure plus wood ash (CmWa), cow manure combined with wood ash plus fertilizers (CmWaF), chemical fertilizers only (DNF) and unamended controls. Soil samples were collected at 0–20 cm depth at bimonthly intervals during 2018–2019. During the two seasons, 54 nematode genera were identified. Cephalobus, and Heterocephalobus (bacterivores), Labronema (omnivore) and Nygolaimus (predator) were abundant in CmDCF, CmWa, CmWaF, and DNF while Aphelenchus and Aphelenchoides (fungivores) were dominant in all treatments. Principal response curve analysis showed that CmWaF significantly reduced the population of Helicotylenchus, Scutellonema and Rotylenchulus during the 2nd and 4th month in the second season. Renyi diversity analysis indicated that CmWaF had higher diversity of omnivores while functional metabolic footprints categorized it as structured in both seasons. Predator-prey analysis suggested that CmWa and CmWaF have the potential to provide suitable conditions for predators, target prey and amplifiable prey biomass. This study provides an insight on the implication of farming practices, on nematode abundance and soil food web in two economically important crops in Kenya. It also provides a basis for exploring the potential role of organic amendments containing cow manure in control of plant parasitic nematodes in maize-beans cropping systems.
Plant parasitic nematode assemblages associated with sweet potato in Kenya and their relationship with environmental variables
(Springer, 2016-11) Karuri, Hannah W.; Olago, Daniel; Neilson, Roy; Njeri, Editah; Opere, Alfred; Ndegwa, Paul
Sweet potato is one of the most important staple food crops consumed in Kenya and throughout Africa but yields are greatly reduced by plant parasitic nematodes (PPN). The aim of this study was to determine the prevalence of PPN in Kenyan sweet potato fields and their relationship with soil and climatic variables. Soil samples were collected from sweet potato fields in Busia, Teso, Kisii, Embu and Makueni counties. Thirteen nematode genera were identified across the five counties with Meloidogyne, Pratylenchus and Rotylenchus being the most prevalent. There was a significant (P <0.05) relationship between PPN abundance and sodium, calcium and iron. Canonical correspondence analysis of climatic variables revealed that the relationship between rainfall and nematode genera was significant (P <0.05) while maximum and minimum temperatures were not significant. This description of PPN assemblages associated with sweet potato in Kenya and their relationship with environmental variables provides a starting point from which appropriate nematode management strategies can be implemented.
Response of Selected Kenyan Rice Cultivars to Infection by Root Knot Nematode (Meloidogyne incognita)
(2019-03) Namu, John; Alakonya, Amos; Karuri, Hannah W.; Nyaga, Justin; Masanga, Joel; Njeri, Editah
Meloidogyne incognita causes huge yield losses in rice which is the third most important cereal crop in Kenya. The aim of this study was to identify M. incognita-resistant rice cultivars from Kenya and relate the responses to known resistance pathways with OsPR1a, OsPAL1, and OsJAMYB as marker genes in rice. Five rice cultivars BW 196, Basmati 217 (Pishori), Sindano, IR 2793-80-1 (grown in lowland irrigated fields), and NERICA 4 (grown in upland rainfed fields) were evaluated for resistance to M. incognita under greenhouse conditions in two separate trials. The number of nematode eggs, reproduction factor (RF), and the level of galling were determined. The RF was used to select resistant cultivars. There was a significant difference (P < 0.001) in the number of eggs, galling index, and RF among the cultivars. NERICA 4, BW 196, and Sindano were classified as resistant with an RF <1. There was differential expression of the three marker genes between susceptible and resistant cultivars. OsJAMYB gene was up-regulated in leaves of all rice cultivars after 1 and 3 days post inoculation (dpi). OsPAL1 was up-regulated in leaves of all varieties at 3 dpi while OsPR1a was down-regulated in leaves of resistant plants at 1 dpi and 3 dpi. These results provide an insight on sources of M. incognita resistance in Kenyan rice and it also forms an interesting starting point for further studies on defense responses of common rice varieties to root knot nematode infection.
Root and soil health management approaches for control of plant-parasitic nematodes in sub-Saharan Africa
(Elsevier, 2021-10) Karuri, Hannah W.
Smallholder farmers in sub-Saharan Africa (SSA) face several challenges that include pests and diseases. Plant-parasitic nematodes (PPN) reduce crop yields and affect their quality. They are an emerging threat to smallholder agriculture with several species attacking economically important crops. In SSA, most PPN control strategies are therapeutic and therefore unsustainable. Cost-effective nematode management strategies that promote soil health and enhance soil suppressiveness against PPN are therefore needed. These strategies can fit into most smallholder cropping systems and in addition to controlling PPN, they also promote soil and plant health and tolerance to other diseases. Most smallholders in SSA still use traditional farming methods although some countries have adopted conservation agriculture (CA) and integrated soil fertility management (ISFM). This review analyzes the potential impact of CA and ISFM on PPN communities and it also provides a concise summary of low-cost PPN control strategies and their efficiency against specific nematode species. Variations in their efficacy is also discussed. The strategies are proposed for adoption across SSA based on site-specific conditions.
A survey of root knot nematodes and resistance to Meloidogyne incognita in sweet potato varieties from Kenyan fields
(Elsevier, 2016-11) Karuri, Hannah W.; Olago, Daniel; Neilson, Roy; Mararo, Enock; Villinger, Jandouwe
The root knot nematode, Meloidogyne is one of the most economically damaging plant parasitic nematode groups, and are widely distributed in Kenyan agro-ecosystems. The aim of this study was to determine the diversity of Meloidogyne species in Kenyan sweet potato fields and identify sweet potato varieties that exhibit resistance to M. incognita. Meloidogyne species were collected from Nyanza, Western, Eastern and Central Provinces of Kenya. Mitochondrial DNA was used to differentiate Meloidogyne species. The most common species in all sampled regions was M. incognita. Meloidogyne hapla was recorded for the first time in Kenyan sweet potato growing areas (Mosocho, Matayos, Teso South, Manyatta, and Nzaui sub-counties), while M. enterolobii was observed in Kiharu, Matayos and Mosocho sub-counties and a novel Meloidogyne sp. was identified in Kiharu sub-county. Seventy-two sweet potato varieties collected from both agricultural fields and research stations in Kenya were evaluated for resistance to M. incognita under greenhouse conditions in two separate trials. Known susceptible (Beauregard) and resistant (Tanzania) sweet potato varieties were included as controls. Responses of sweet potato varieties to M. incognita infection was assessed by the number of eggs present and level of galling on a scale of 1e5, where 0 ¼ 0 galls and 5 100 galls. The reproduction index (RI) was used to classify the varieties as resistant or susceptible. There was a significant difference (P < 0.001) in the number of eggs, GI and RI among the varieties tested. Forty nine sweet potato varieties were considered very resistant and may be used in breeding programs to incorporate resistance against M. incognita into commercial cultivars of sweet potato or to use them in crop rotation programmes for management of RKN. The results on Meloidogyne species diversity in Kenyan sweet potato fields will also be useful in nematode management programs.
Using science to empower farmers: Hunting down the invisible worms threatening Kenyan crops
(2020-10) Karuri, Hannah W.
What comes to mind when you think of climate change? Perhaps it’s melting ice shelves and droughts or raging wildfires and floods. To see the large-scale manifestations of a warming planet, we need not look far. On a microscopic level, however, climate change paints a very different picture. For Dr Hannah Karuri, a nematologist and senior lecturer at Kenya’s University of Embu, the most harmful impacts of climate change are those that we cannot see nor feel – the invisible worms.

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