Department of Crop Science

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Allelic Variation of Terpene Synthases Drives Terpene Diversity in the Wild Species of the Freesia Genus.
(2023-03-18) Bao, Tingting; Kimani, Shadrack; Li, Yueqing; Li, Hongjie; Yang, Song; Zhang, Jia; Wang, Qiuyue; Wang, Zhaoxuan; Ning, Guogui; Wang, Li; Gao, Xiang
Terpene synthases (TPSs) play pivotal roles in conferring the structural diversity of terpenoids, which are mainly emitted from flowers, whereas the genetic basis of the release of floral volatile terpenes remains largely elusive. Though quite similar in sequence, TPS allelic variants still function divergently, and how they drive floral terpene diversity in closely related species remains unknown. Here, TPSs responsible for the floral scent of wild Freesia species were characterized, and the functions of their natural allelic variants, as well as the causal amino acid residues, were investigated in depth. Besides the eight TPSs previously reported in modern cultivars, seven additional TPSs were functionally evaluated to contribute to the major volatiles emitted from wild Freesia species. Functional characterization of allelic natural variants demonstrated that allelic TPS2 and TPS10 variants changed enzymatic capacity while allelic TPS6 variants drove the diversity of floral terpene products. Further residue substitution analysis revealed the minor residues determining the enzyme catalytic activity and product specificity. The clarification of TPSs in wild Freesia species reveals that allelic TPS variants evolved differently to determine the interspecific floral volatile terpenes in the genus and might be used for modern cultivar improvement.
The anti-inflammatory properties of Kenyan tea
(2015) Karori, S.M .; Ngure, R.M.; Wanyoko, J.K.; Wachira, F.N.
An in vivo study was carried out to determine the effect of different types of Kenyan tea extracts on male Swiss albino mice infected with Trypanosoma brucei brucei isolate KETRI 2710. The isolate produced a similar clinical picture after a pre-patent period of five days post-infection (DPI). Parasitemia levels in the untreated mice and those given different tea developed exponentially at similar rates reaching the peak of parasitemia 8 DPI. Between 9 and 13 DPI parasitemia decreased more rapidly in tea treated compared to the untreated mice which indicated that tea lowered parasitemia. Anaemia indicated by a fall in erythrocyte packed cell volume (PCV) occurred within 4 DPI and remained below the normal levels until the terminal stages of the disease. A significant difference (P < 0.05) was observed 11 DPI between the tea treated and the untreated mice indicating that tea enhanced resistance to erythrocyte destruction. Mice treated with tea exhibited significantly (P < 0.01) reduced parasite induced hypoalbuminemia as compared to the untreated demonstrating that tea ameliorated inflammation induced by T. brucei brucei. Black tea, which is the principle tea product from Kenya, displayed remarkable properties some even comparable to those of green tea. Tea was more efficacious than dexamethasone, an established anti-inflammatory drug, demonstrating its therapeutic potential.
Antimicrobial acitivity of extracts from Tephrosia vogelii Hook F.
(2007-01-29) Wanga, B. N.; Akenga, T.; Imbuga, M.; Gitonga, L .; Olubayo, F.; Namungu, P.
The dichloromethane extracts of the root and leaf of Tephrosia vogelii Hook F. (Family: Papilionaceae) grown in Kenya, were subjected to antimicrobial assays against Staphylococcus aureus, Escherichia coli and Fusarium phoseolida. The minimum inhibition concentrations (MIC) ranged between 0.25 to 6.4 μg/ml for all the microorganisms tested. The crude root and leaf extracts were also toxic to the brine shrimps, organisms used as indicators of toxicity (LC50: 0.960; 0.958 μg/ml, respectively). Chromatographic separation led to the identification of (6aß, 12aß, 5'ß)-6a, 12a, 4',5'-tetra hydro-2,3-dimethoxy 5'-ß- isopropenyl–furano (3',2': 8,9)-6H-rotoxen-12-one, (rotenone) in 9.75% yield, (roots), and 11.75% (leaves). Characterisation was achieved by use of spectroscopic techniques and comparison with rotenone standard and literature data. Novel HPLC conditions for purification of rotenoids were established. The MIC of rotenone against the tested microbes was found to be 5.2 and 1.0 μg/ml for Staphylococcus aureus and Escherichia coli respectively, while the LC50 against the brine shrimps was found to be 3.20 μg/ml. The findings indicate that the extracts of T. vogelii contain metabolites that have antimicrobial activity comparable to other medicinal plants.
Antioxidant, antimicrobial and synergistic activities of tea polyphenols
(2015) Koech, K.R.; Wachira, F.N.; Ngure, R.M.; Wanyoko, J.K.; Bii, C.C.; Karori, S.M.; Kerio, L.C.
Microbial resistance to conventional antibiotics has become an increasing global problem and there is a need to find out novel, potent antimicrobial agents with alternative modes of action as accessories to antibiotic therapy. This study investigated the antioxidant, antimicrobial and synergistic properties of tea polyphenols. The tea germplasm from Kenya, China and Japan that are grown in Kenya were characterised for their biochemical profiles. The total phenolic content, theaflavins and thearubigins content of different tea products used in this study were determined spectrophotometrically according to Folin-Ciocalteus and flavognost methods respectively. The individual catechin contents were characterised by high performance liquid chromatography (HPLC) and identified according to their HPLC retention times, elution order and comparison with authentic standards. The antioxidant activity of tea polyphenols was determined using UV-Vis spectrophotometer on its ability to scavenge 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical. The Agar Disc Diffusion method was used to screen for antimicrobial and synergistic activities of the tea liquors. Black, green, purple coloured leaf and white (silvery tips) tea products characterised for their biochemical profiles differed significantly in the levels of total polyphenols, total catechins, catechins fractions, theaflavins and thearubigins (P ≤ 0.05). Green, purple coloured leaf (aerated) and black tea from terminal buds and white tea products analysed in this study exhibited slightly higher antioxidant activity compared to black tea. The different types of tea products assayed in this study exhibited significant influence on the inhibition zone diameters against bacteria and fungi exposed to the tea extracts. Methicillin and penicillinase resistant S. aureus ATCC 25923, C. albicans ATCC 90028 and a clinical isolate of C. neoformans were more susceptible to all tea extracts than E. coli and S. typhi. There was synergism between most tea extracts and penicillin G against methicillin and penicillinase resistant S. aureus ATTC 25923.
Article Navigation JOURNAL ARTICLE Evidence for Potential of Managing Some African Fruit Fly Species (Diptera: Tephritidae) Using the Mango Fruit Fly Host-Marking Pheromone
(Entomological Society of America, 2012-12-01) Kachigamba, Donald L.; Ekesi, Sunday; Ndung'u, Mary W.; Gitonga, Linus M.; Teal, Peter E. A.; Torto, Baldwyn
We investigated conspecific and heterospecific oviposition host discrimination among four economically important fruit fly pests of mango in Africa (Ceratitis capitata, Wiedemann; C. fasciventris, Bezzi; C. rosa, Karsch, and C. cosyra, Walker) with regard to host-marking behavior and fecal matter aqueous solutions. The objective of the study was to get insight into the potential of managing these pests using the host-marking technique. Observations were done on mango slices marked by the flies and treated with aqueous solutions of fecal matter of the flies, respectively. In both host-marking and fecal matter experiments, C. cosyra, which is the most destructive species of the four on mango, was exceptional. It only discriminated against hosts treated with its fecal matter but with lower sensitivity while C. capitata and C. fasciventris discriminated against hosts marked by it or treated with its fecal matter and with higher sensitivity. Our results provide evidence for potential of managing some of the major fruit fly species infesting mango in Africa using the host-marking pheromone of the mango fruit fly, C. cosyra.
Assessing the effect of grading on the in vitro availability of Fe, Zn, Cu, Pb and Cd from CTC black tea
(2015) Moseti, K.O.; Kinyanjui, T.; Wanyoko, J.K.; Wachira, F.N.
In vitro analyses of trace element content in biological systems play an increasingly important role in assessing the environmental impact on health. A quantitative study of five trace elements namely Fe, Zn, Cu, Pb and Cd in cut, tear and curl (CTC) black Tea of different grades randomly sampled from four tea growing countries in East Africa, viz., Kenya, Uganda, Rwanda and Tanzania was carried out. The total element content as well as the water extractable content of the tea samples was done by Atomic Absorption Spectroscopy (AAS). Data obtained was analyzed using Graph-pad Prism statistical software for Windows, version 5.0 and P < 0.05 considered to be statistically significant. The significance of the difference between means for black tea and tea infusions was determined by one way ANOVA and the least significant difference test was used for mean separation where significant differences were recorded among group means. It was observed that tea contains the studied elements and only a very small portion of the total element content lixiviates into tea liquor during tea making process. The general extractability pattern of the elements studied was in the order Fe > Zn > Cu > Pb > Cd, indicating that tea is an important dietary source of Fe, Zn and Cu. Taking into account the high tea to water ratio used in preparing the analysed tea extracts, these data is best regarded as the extractability potential of the tea liquor and does not reflect the actual concentrations contained in the tea liquor that we actually consumed. However, the need to enact safety guidelines with regard to the liquor element composition is imperative.
Assessment of Production Constraints and Contribution of Avocado to Food Security and Income in the Mount Kenya Region, Kenya
(2023) Kamotho, Grace N.; Asiko, Lydiah A.; Kibanyu, James K.; Kinyua, Phares R.; Karaya, Rebecca N.; Muthee, Patrick M.; Mwathi, Zipporah M.
Avocado (Persea americana Mill.) belongs to the family Lauraceae and it is an important crop to rural communities and economies in Kenya. Currently, avocado is grown in several agro ecological zones mainly by small-scale growers (85%) who grow it for subsistence, local markets and export. About 70% of avocado is grown in Central and Eastern region of Kenya. Central region produces 40%, Eastern 28%, Western 13%, Rift Valley 10%, Nyanza 6%, Coast 2% and Nairobi County 1%. The main production areas are Muranga, Kiambu, Thika, Embu, Meru, Taita Hills and Kitale. The aim of this study was to assess the production constraints and contribution of avocado to food security and income in Mount Kenya region. The study population comprised of smallholder avocado farmers. Purposive sampling was done in selecting highest producing sub-counties of avocado in Nyeri, Muranga and Embu counties. Simple random sampling was used to select 40 smallholder farmers from each of the selected sub counties who participated in the survey. Data was collected using a structured questionnaire and analysed using SPSS computer package. Results indicated several constraints in the production of avocado including pests and diseases, lack of quality planting material, poor soils, lack of technical knowledge by avocado farmers and lack of well-structured marketing system. The study identified a gap in value addition of avocado in Kenya. It was also demonstrated that avocado contributes highly to household income and food security. The crop should therefore be accorded priority by policy makers and more research needs to be encouraged especially in the management of pests and diseases. Capacity building to avocado growers should be routinely carried out so as to avoid the many challenges that emanate from lack of technical knowledge. Intervention in value addition of avocado is an aspect that Kenyan county governments need to engage in by investing in cottage industries on avocado processing.
An Assessment Of The Physiological Quality Of Sorghum (Sorghum Bicolor L Moench) Seeds Planted By Farmers In Bomet District Of Kenya
(African Journal of Food, Agriculture, Nutrition and Development, 2012-08) Ochieng, L.A; Mathenge, P.W.; Muasya, R.
Sorghum (Sorghum bicolor L. Moench) is an important crop that enhances food security in a region. As a food crop, sorghum is nutritious, containing starch (75-79%) as the major component, followed by protein (6.0-16.1%) and oil (2.1-5.0%). Despite the crop’s versatility, it is regrettable that sorghum yields are still fairly low in Bomet District of Kenya. One of the constraints associated with low yields is the accessibility to good quality seeds by farmers. It was assumed in this study that use of low quality seed was among the factors that could be significantly affecting the low production of sorghum in the district. This study focused on the physiological quality of seed which refers to the germination capacity, viability, characteristics related to dormancy and vigour of the seed. A total of 100 farmers were interviewed and 80 seed samples were obtained from 80 farmers. The seeds were subjected to viability and vigour quality tests. These tests included germination (as a viability test); mean germination time and electrical conductivity tests (as vigour tests). About 29% of the seed samples taken for germination test were below the laboratory standards as stipulated in the seeds and Plant Varieties Act (CAP 326). Critical electrical conductivity values and critical mean germination time values were derived during the study. In accordance with the critical values arrived at in this study, 27.5% of the seed samples showed relatively high electrical conductivity readings and 36.3% of the seed samples showed longer mean germination time. However, 11.3% of the seed samples showed high germination percentages of above 90%. Since about 29% of farmers seeds were of bad physiological quality, it was concluded that this proportion of seed can result in poor yields and hence cause food insecurity to the people of the society, and thus requires further consideration for improvement. This study recommends that further research be conducted on the genetic, physical and sanitary quality aspects of seed planted by farmers in Bomet District so that a definite conclusive statement about the quality of seed planted by farmers in the District can be made.
Biocontrol of Fusarium root rot in beans by antagonistic Trichoderma fungi
(International Journal of AgriScience, 2013-07) Muriungi, J.S; Mutitu, E.W.; Siboe, M.G.
Common bean (Phaseolus vulgaris) is one of the most important economic crop which is attacked by serious diseases such as Fusarium root rot. In this study, the efficacy of Trichoderma viride and T. koningii were evaluated for the suppression of Fusarium oxysporum causing root rot of beans in vitro and disease control under greenhouse condition. Three food carriers - broken dehulled rice grain, sorghum seeds, and vermiculite were also evaluated for suitability as growth and delivery media for Trichoderma isolates as determined by the sporulation ability and root rot control respectively. In vitro studies resulted in effective suppression of F. oxysporum by the two Trichoderma isolates. Saprophytic growth on rice and sorghum was good at two weeks but poor on vermiculite. T. viride in half broken dehulled rice produced excellent bean root rot control as measured by disease severity at 7th week and was significantly (P≤0.05) better than standard seed dresser Murtano (20% Thiram and 20% Lindane); T . koningii and T . viride in sorghum, and T. koningii in rice had moderate disease control whilst the two Trichoderma isolates in vermiculite had poor disease control. There was some positive correlation between saprophytic growth of Trichoderma isolates in different carriers in the laboratory and their suppression of Fusarium root rot in the greenhouse. The results of this study indicates that potential exist for management of Fusarium root rot in beans by antagonistic Trichoderma isolates in their respective carriers and may form part of IPM for bean root rot.
Biological control agents of aphids (Homoptera: Aphididae) on potatoes (Solanum tuberosumL) in Kenya
(2010) Machangi, J. M.; Gitonga, L. M.; Nderitu, J. H.; Maniania, N. K.; Kabira, J. N.
A field survey was conducted in four major potato growing areas in Kenya (Kiambu, Nyandarua, Meru and Molo Districts) during January and February, 2008 (short rains crop) and June 2008 (long rains crop) to determine the occurrence of predators, parasitoids and pathogens of the aphids Myzus persicae Sulzer and Aphis gossypii Glover in potato crops. In each of the four areas, 30 potato farms distributed in different parts of the survey area were selected at random for the surveys. Insects collected were brought to the laboratories at the International Centre of insect physiology and Ecology (icipe), Nairobi, for identification and fungal infection. For isolation of fungal pathogens, dead aphids were transferred on moist filter paper placed on sterile Petri dishes to allow the growth of the fungus on the surface of the cadaver, after which fungus was transferred on artificial media for isolation. Four aphid species, M. persicae, A. gossypii, Macrosiphum euphorbiae Thomas and Aulacorthum solani Kaltenbach were identified in all the four survey areas. Sixteen predator species of the aphids were identified. The most prevalent were the ladybeetles Harmonia axyridis (Pallas) and Hippodamnia convergens Guérin-Méneville (Coleoptera: Coccinellidae), followed by the minute pirate bugs, Orius spp. (Heteroptera: Anthocoridae) and the aphid eating gall midge Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae). Three hymenopteran parasitoid species (Braconids followed by Chalcids then the Ichneumonids) and four fungal pathogen species, Beauveria bassiana Balsamo (Ascomycota: Hypocreales), followed by Verticillium lecanii Zimmermann (Hypocreales: Incertae sedis), Metarhizium anisopliae (Metsch.) Sorokin (Deuteromycotina: Hyphomycetes) then Pandora neoaphidis (Remaudière &Hennebert) Humber (Zygomycetes:Entomophthorales) were identified in all four areas of the field survey.
Biorational Preservation of Rose (Rosa hybrida L.) Cut-Flower Using Stevia (Stevia rebaudiana B.) and Thyme (Thymus vulgaris L.) Extracts
(SciPress Ltd, 2018) Kiige, John Kamanthi; Mathenge, Patrick Wachira; Kavoo, Agnes Mumo
Rose cut flower is one of the widely grown cut flowers in Kenya. However, most roses have a challenge of short vase life. This study aimed at determining the efficacy of plant extracts from thyme and stevia in preservation of rose cut-flowers. Two rose cut-flower cultivars; ‘radiance and ‘high & sparkling’ were subjected to stevia and thyme extracts each at three levels (0.2, 0.4, and 0.6gL-1). Thyme extracts at a concentration of 0.2 gL-1 significantly (p≤001) extended the vase life of rose cut flower by 3.5 days and floral absorption rates by 10.4% compared to the commercial preservative (chrysal) at the same concentration rates. Application of higher doses (0.4gL-1 and 0.6gL-1) of plant extracts led to shorter vase life (6 days) of rose cut flower and maximum bent neck records at day 8. The response of rose cut flower to the treatments did not vary between cultivars. The results from this study indicate that thyme extracts offer an attractive alternative to the use of chemical floral preservatives for prolonging the vase life and enhancing quality of rose cut flower. The efficacy of extracts is however depended on the concentration level with 0.2gL-1 dosage recording the best results.
Bradyrhizobium inoculation has a greater effect on soybean growth, production and yield quality in organic than conventional farming systems
(2021-06-22) Gitonga, Nicholas Mawira; Njeru, Ezekiel Mugendi; Cheruiyot, R. C.; Maingi, John
Globally, organic farming and bradyrhizobia inoculation are gaining popularity as agronomically and environmentally sound soil management strategies with great potential to alleviate declining soil fertility, maintain environmental quality and enhance soybean production. However, the role of bradyrhizobia in organic farming system is poorly understood. Field experiment was conducted to evaluate the effects of bradyrhizobia inoculation and organic farming on growth parameters and yield quality of soybean varieties: SC squire, SB19 and Gazelle. The experimental treatments included native bradyrhizobia, commercial Bradyrhizobium japonicum, mixture of native + commercial bradyrhizobia and uninoculated control. The experimental design was a split-split plot, with three replications. The results demonstrated significant improvement in soybean nodule dry weight (NDW), shoot dry weight (SDW) and seed dry weight (SEDW) following bradyrhizobia inoculation. Remarkably, organic farming significantly out-performed conventional systems in nodulation, SDW and SEDW. Moreover, seed nutrient content differed depending on farming system; where nitrogen, phosphorus, potassium and organic carbon were higher in organic farming. Soybean varieties differed significantly on SDW, NDW and SEDW; where SC squire performed better than SB19 and Gazelle. The results demonstrate the importance of organic farming and bradyrhizobia inoculation in enhancing soil fertility, yield production and quality, a key step towards sustainable food production.
Community Monitoring of Forest Carbon Stocks and Safeguards Tracking in Kenya: Design and Implementation Considerations
(Scientific Research Publishing Inc, 2015-04) Nduru, Gilbert M.; Ucakuwun, Elias K.; Gichu, Alfred N.; Kinyanjui, James M.; Wegulo, Francis N.; McCall, Michael K.; Muchemi, Julius G.
This paper investigates modalities required to design and implement community monitoring of forest carbon stock changes and safeguards implementation in Kenya. General principles and elements were drawn from the UNFCCC REDD+ policy frameworks for developing modalities and procedures for designing community forest monitoring system. The paper utilised policy analysis approach used to derive monitoring goals and objectives by assessing the compatibility of Kenya’s policy and legislative framework with monitoring elements provided in the UNFCCC REDD+ policy mechanism. The elements included monitoring goals, objectives, questions, indicators, and meth- ods and tools. Two goals were identified which included, reduction of forest carbon emissions (ER) and monitoring of multiple social and environmental safeguards (SG). Five ER related objectives were identified to include: forest reference emission levels or forest reference levels, drivers of deforestation and forest degradation, Land use activities, eligible ER actions and estimation of forest emissions. Six objectives guiding SG were identified to include: policy, governance, human rights, socio-economic, biodiversity and environmental concerns. Corresponding questions to the goals and objectives were systematically designed. In turns, indicators, depicting quantitative and qualitative measurements, which best provided answers to questions were identified. The various methods and tools used by communities around the world in providing data and information re- quired to satisfy the indictors were identified through literature review. The review identified four methods and tools that included: Remote Sensing and GIS, GPS survey, smartphone survey and Ground trothing. Smartphone and cloud-based server technology were found to be the recent emergent tools in aiding community monitoring of REDD+ projects. The paper argues that local communities and indigenous peoples have the capability and capacity to monitor and undertake forest carbon monitoring and tracking of implementation of safeguards if supported with relevant training; compensated for the time, labour and knowledge they contribute to the process; pro- vided with feedback and involved decision making process.
A comparative analysis of effects of black and purple tea on iron absorption in adolescent pregnant population
(2015) Asiko, L.
Adolescent pregnancy is a major public health issue in developing countries. It is associated with unique nutritional requirements as well as risk of micronutrient deficiencies. Some of the foods and drinks ingested during pregnancy have been known to affect the absorption of much needed micronutrients and consequently compromise the health of both the mother and the growing foetus. There is scientific evidence to suggest that tannins and phytates in tea and in cereal-based foods inhibit iron absorption and predispose the mother to iron-deficiency disorders such as anaemia and predispose the unborn infant to low-birth weight. In Kenya, the most predominantly grown and consumed tea type is black tea. Studies have shown that consumption of black tea with meals can decrease iron absorption by up to 50%. Purple tea is reported to contain anthocyanins, which have antioxidant effects that provide anticancer benefits, improve vision, and better cholesterol and blood sugar metabolism. If purple tea is to be preferred to the traditional black tea, one has to ascertain that the iron inhibiting tannins are either in low quantities or altogether absent from the purple tea. Eating and drinking habits among pregnant women may exacerbate anaemia prevalence and or other more serious foetal problems. This paper discusses the feeding habits of a pregnant adolescent population and assesses the possible effects of tea drinking on iron absorption and maternal health. The paper found out that black tea drinking in pregnancy, and during meals, is rampant and negatively affects iron absorption. Knowledge about the health benefits of purple tea is not only scanty and where (the knowledge) is available the tea is not readily available for purchase. The paperrecommends awareness of nutrition education to improve the feeding habits.
Constraints to On-Farm Maize (Zea mays L.) Seed Production in Western Kenya: Plant Growth and Yield
(ISRN Agronomy, 2012) Wambugu, P.W.; Mathenge, P.W.; Auma, E.O.; VanRheenen, H.A.
Studies have shown that that about 85% of maize farmers in Western Kenya plant local varieties with about 80% using own farm-saved seeds. The production system is characterized by late harvesting, heavy striga infestation, use of local varieties, and low-soil fertility. The objective of this study was to test an on-farm seed production system which would help improve yield and quality of farm saved seeds. The trials were set up in a factorial design fitted as random complete block design. There were 3 factors each at 2 levels: time of harvest, variety choice, and fertilizer application. Fertilizer application led to an 88% increase in yield, 54% increase in number of seeds per cob, and 14% increase in 100-seed weight. Fertilizer application also led to an increase in seed vigour and viability. Yield differences between the 2 varieties were not significant. The correlation between 100-seed weight and seed vigour was significant showing that heavy seeds were more vigorous. Nitrogen application was therefore recommended for increasing yields and for producing vigorous seeds but should be done with caution to avoid lodging as witnessed. This study also noted that farmers are rational and their decisions are usually based on strong economic considerations.
Control of Bacterial Wilt in Tomato Using Chitosan Intercalated with Tea Extracts.
(OJS/PKP, 2022-04-21) Gatahi, Dennis; Kihurani, Agnes; Harrison, Wanyika
In this study, tea extracts were intercalated in chitosan gel to enhance the inhibitory effect of the complex on bacterial wilt in tomato. The disease caused by Ralstonia solanacearum can result in 100% crop loss under severe infection. Chitin was ground into powder of 0.1 mm size, deacetylated using concentrated NaOH solution and tea extracts from green, purple and black tea adsorbed through rotary evaporation. Confirmatory tests on effective adsorption were done using FTIR and XRD, while bioassay experiments were performed to determine efficacy of the chitosan intercalated with crude tea extracts (CICTE) on the pathogen and tomato growth. In vitro and In situ tests were carried out in growth chambers and greenhouse respectively. The greenhouse trials were conducted for a period of 2 years in three sites i.e. Gatundu, JKUAT and Makuyu. The bioassays demonstrated significant (p < 0.05) reduction of R. solanacearum turbidity marked by change of optical densities (OD) from 3.55 to 1.04. In addition, there was significant (p < 0.05) inhibition of the cultured R. solanacearum and reduced wilt incidence in tomato plants treated with CICTE and later inoculated with the pathogen. Tomato plants treated with CICTE also recorded a significantly (p < 0.05) higher yield compared to the control. The study therefore recommends utilization of CICTE as an effective and environmentally safe biopesticide for the devastating bacterial wilt pathogen.
The Critical Onion Growth Stages For Selective Protection From Thrips Tabaci Lindeman (Thysanoptera:Thripidae) Infestation
(Kenya Agricultural Research Institute, Nairobi (Kenya), 2006-01) Waiganjo, M. M.; Sithanantham, S.; Mueke, J. M.; Gitonga, L. M.
Field trials were conducted during 2000-2001 at KARIandrsquo;s Mwea-Tebere and Kiboko farms to establish the effect of onion thrips, Thrips tabaci Lindeman on onion bulb yields and to identify the critical onion growth stage for selective protection from the pest infestation. Yield reductions of 59 and 27% were recorded in the first and second crops respectively at Mwea-Tebere, but no significant yield reductions were observed in a third crop grown at Kiboko with low thrips infestation. A significant onion yield response to thrips infestation was observed during the 2nd month after transplanting (bulb-formation) and 3rd month after transplanting (bulb-enlargement), but no significant response was observed during the 1st month (pre-bulbing) and 4th month (maturation stage). Onion protection during bulb-formation and enlargement stages only, resulted in higher marginal returns than full season pesticide application. The studies suggest that control recommendations for onion could be refined to optimize need-based protection.
Crop Production in Irrigation Schemes in Turkana County, Kenya, Before and During COVID-19 (2018-2021)
(2023-08-11) lLokuruka, Michael N. I.
Turkana County, located in the northwest of Kenya, is an arid county and the poorest in the country, with a poverty index of 79.3% vs. 34.4% for the country. Due to its aridity, crop production is severely constrained and the County is a net importer of foodstuffs, except beef, mutton and camel meats. Crop production in the operating irrigation schemes depends on water from retreat flooding in March-May and any that is let into and retained in canals when the seasonal rivers are flowing. This project aimed to assess the influence of COVID-19 and other undetermined factors on crop production in 10 irrigation schemes along the Tirkwell River, over the period 2018-2021. The study administered a semi-structured questionnaire to 104 randomly selected farmers, who owned farm plots in the irrigation schemes. One-on-one interviews were held, due to the high level of illiteracy of the respondents. Twelve elders and administrators were the key informants. The study established that sorghum was the dominant crop grown in 9 out of the schemes, except in Kooliyoro-Kaaiteese, where maize was the main crop. Other crops in declining order by production volume included cowpeas, green grams, black grams and in Keekoroe-ngole, some green vegetables. The weight of the dominant crop and other crops varied significantly (p≤ 0.05) in the same irrigation scheme across the years of interest for this study, and also across the irrigation schemes over the production period. The results of the study showed that COVID-19 breakout did not affect crop production in the irrigation schemes studied. Farmer poverty level, lack of expert extension services, use of uncertified and reused seed, unreliable water supply, and regular droughts affected crop production. The most productive 3 schemes in descending order by crop production volumes were Nanyee, Napool andKeekoroe-ngole, while Naremit was the least productive. Crop production suffers from long-term sustainability in all the schemes for most of the above reasons. To improve crop production, the study recommends the provision of expert extension services, a steady water supply, annual donation of certified seeds, improvement in crop-care services, streamlining crop marketing services and the upgrade of governance and management capability in the irrigation schemes.
Do Mixed-Species Legume Fallows Provide Long-Term Maize Yield Benefit Compared with Monoculture Legume Fallows?
(Wiley, 2009-11-01) Ndufa, James K.; Gathumbi, Stanley M.; Kamiri, Hellen W.; Giller, Ken E.; Cadisch, Georg
The deliberate planting of fast-growing N2–fixing legume monoculture species in rotation with cereal crops can be an important source of N for soil fertility replenishment. We hypothesized that mixed-species fallows have a higher potential of giving long-term residual benefits in terms of biomass, nutrients, and quality of residuals leading to long-term nutrient supply to postfallow maize (Zea mays L.) crops. To test these hypotheses, two experiments were established in farmers' fields on very fine Kandiudalfic Eutrudox soils with monoculture and mixed-species fallows. Treatments included: sesbania [Sesbania sesban (L.) Merr.], crotalaria (Crotalaria grahamiana Wight and Arn.), pigeonpea [Cajanus cajan (L.) Millsp.], siratro [Macroptilium atropurpureum (DC.) Urb.], and calliandra (Calliandra calothyrsus Meissn.) as monoculture-species fallow and mixture fallows of sesbania + crotalaria, sesbania + pigeonpea, sesbania + siratro, or sesbania + calliandra compared with continuous maize cropping with or without N fertilizer, and natural weed fallow. Total aboveground biomass ranged from 4.1 to 20.5 Mg ha−1 for monoculture and 7.8 to 23.3 Mg ha−1 for mixed-species fallows. Recyclable fallow biomass N ranged from 70 to 313 kg ha−1 and there was a positive interaction in some mixtures leading to increased N accumulation. Postfallow maize yields for fallows over five cropping seasons were 161–272% or 61–103% higher when compared with continuous maize without or with N fertilizer, respectively. Long-term postfallow effects on maize yield were linearly related to the amount of recycled fallow N yield. Thus, choice of fallow species to mix should be primarily driven by a better risk management strategy and an increased basket of multiple products and services.
Dual inoculation of soybean with Rhizophagus irregularis and commercial Bradyrhizobium japonicum increases nitrogen fixation and growth in organic and conventional soils
(AIMS Agriculture and Food, 2021) Gitonga, Nicholas Mawira; Koskey, Gilbert; Njeru, Ezekiel Mugendi; Maingi, John M.; Cheruiyot, Richard
Soil amendment with beneficial microorganisms is gaining popularity among farmers to alleviate the decline ofsoil fertility and to increase food production and maintain environmental quality. However, farm management greatly influence soil microbial abundance and function, which overly affects crop growth and development. In this work, greenhouse experiments involving soybeans were conducted to evaluate the effects of bradyrhizobia and arbuscular mycorrhizal fungi (AMF) dual inoculation on nodulation, AMF root colonization, growth and nutrient acquisition under contrasting farming systems. The experimental treatments were AMF and/or bradyrhizobia inoculation and dual inoculation on SC squire soybean variety. The exotic AMF inoculants used were Funneliformis mosseae (BEG 12) and Rhizophagus irregularis (BEG 44) while bacteria were commercial Bradyrhizobium japonicum (USDA110) and native bradyrhizobia isolates. Experiments with soil samples from organic and conventional farms were set out using a completely randomized design with three replicates. The results demonstrated that bradyrhizobia and AMF dual inoculation consistently and significantly enhanced soybean nodule dry weight (NDW), shoot dry weight (SDW) and AMF root colonization compared with individual bradyrhizobia, AMF and non-inoculated control. Moreover, organic soil significantly (p = 0.001) increased soybean SDW, NDW and AMF root colonization compared to conventional soil. Remarkably, shoot nutrients content differed in organic and conventional farming where, shoot nitrogen, phosphorus, potassium and organic carbon were 479 AIMS Agriculture and Food Volume 6, Issue 2, 478–495. higher in organic farming than the latter. Among individual inoculants, Rhizophagus irregularis outperformed Funneliformis mosseae, while commercial Bradyrhizobium japonicum showed higher performance than native bradyrhizobia. Our results demonstrated the importance of organic farming, AMF and bradyrhizobia dual inoculation in enhancing soybean growth and nutrient acquisition. However, field trials should be assessed to determine the good performance of bradyrhizobia and AMF dual inoculation in organic farming before being popularized and adopted by farmers as a sustainable agronomical management strategy to increase soil fertility and food productivity.