Browsing by Author "Lengai, Geraldin"

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Activity of ethanolic extracts of spices grown in Tanzania against important fungal pathogens and early blight of tomato
(Bulgarian Journal of Agricultural Science, 2021-12) Lengai, Geraldin; Mbega, Ernest; Muthomi, James
The nutritional and economic value of tomato is universally recognized yet its production in many regions is still low due to, among other reasons, fungal diseases. Farmers have desperately relied on synthetic chemical pesticides to manage the dis- eases but the chemicals, in spite of their efficacy, are associated with residual detrimental effects on human health and environ- ment. The objective of this study was to evaluate the antifungal activity of selected spices against important fungal pathogens of tomato. Bioactive compounds from seven spices namely clove, black pepper, turmeric, ginger, lemongrass, cinnamon and cardamom powders were extracted in ethanol and tested for antifungal activity against Alternaria solani, Fusarium oxysporum f. sp lycopersici and Pythium sp. in poisoned food bioassay. The most active spice extracts were further tested for efficacy against early blight of tomato under field conditions. All extracts were significantly active against the tested fungal pathogens by about 85%. Clove extract was the most active against all the pathogens inhibiting their growth 100%. Ginger, black pepper and turmeric extracts inhibited growth of all the pathogens by between 74-80%. Lemongrass extract was the least active with an antifungal activity of about 49%. Under field conditions, clove remained active in reducing early blight disease load by about 36% compared to the negative control. The antifungal activity demonstrated by the spice extracts is an indication that they could be relied upon for disease control and this study recommends their consideration, especially clove, for formulation into a botanical fungicide for management of early blight of tomato.
Activity of extracts from selected Tanzanian spices on major fungal pathogens and blight diseases of Tomato
(NM-AIST, 2021-08) Lengai, Geraldin
Tomato (Solanum lycopersicum L.) is affected by many fungal diseases and farmers rely on synthetic pesticides for management. Detrimental effects associated with injudicious use of chemical pesticides have caused a demand for alternative crop protection products. The objective of this study was to evaluate the antifungal activity of selected spices against major fungal pathogens and blight diseases of tomato. An ethnobotanical survey for ginger and turmeric and evaluation of awareness of botanical pesticides use and collection of commonly consumed spices was conducted in Tanzania. Ethanolic extracts from spices were prepared by maceration and tested for antifungal activity in posisoned food bioassay against Phytophthora infestans, Alternaria solani, Fusarium oxysporum f.sp. lycopersici and Pythium spp in vitro, their effect on seed germination and efficacy on severity of early and late blight diseases of tomato in. The most active extracts were fractionated in solvents with varied polarity, analyzed for biochemical composition and tested for fungicidal activity. Results indicated that among the tested spices, clove extract was the most active, inhibiting all the fungal pathogens (100%). Combined effect of the most active extracts showed that clove combined with either ginger, black pepper or turmeric inhibited growth of P. infestans (100%). The activity of solvent fractions was lower compared to the crude ethanolic extracts, except for clove fractioned in n hexane which completely inhibited the growth of P. infestans. Therefore, the most active compounds were better extracted in ethanol. Gas chromatography- mass spectrometry analysis of the clove’s n- hexane fraction showed high abundance of eugenol (74%) which is likely to be responsible for the high antifungal activity. High concentrations of the spice extracts deterred and slowed germination but low concentrations stimulated seed germination of up to 98%. Under field conditions black pepper extract reduced severity of late blight by 40% while clove extract reduced severity of early blight by 35% compared to the untreated control. The findings herein are proof of activity of spice extracts under in vitro and field conditions. This study recommends that the most active extracts be considered for development of a broad botanical fungicide for management of fungal diseases of tomato.
In vitro and field evaluation of selected spices as botanical fungicide for management of Phytophthora infestans, causative agent for late blight in tomato
(Taylor & Francis online, 2022-11-26) Lengai, Geraldin; Muthomi, James; Mbega, Ernest; Cheseto, Xavier
Late blight of tomato, caused by Phytophthora infestans, is responsible for massive losses in yield of open field-grown tomato and is managed by use of synthetic fungicides. The rising demand for food safety calls for alternative yet effective crop protection products. Using a bioassay-guided approach the antifungal properties of ethanolic extracts of seven spices was evaluated and the constituents of the most inhibitory fraction determined using coupled gas chromatography-mass spectrometry. Clove extract was the most active and inhibited (100%) growth of P. infestans followed by black pepper (91%) turmeric (87%) and ginger (85%). The hexane fraction of clove extract equally inhibited growth of P. infestans 100%. The spice extracts reduced severity of late blight by between 29% and 40% with black pepper being the most efficacious under field conditions. These findings show the fungicidal potential of selected spices for the management of late blight of tomato.
Pesticidal and Medicinal Value of Turmeric and Ginger in Tanzania and Their Antifungal Activity against Phytopathogens
(Scientific research an academic publisher, 2025-02) Lengai, Geraldin; Mbega, Ernest; Muthomi, James
Use of synthetic pesticides to manage crop pests has had a toll on human health, environmental safety and farmer’s income creating a need for alterna- tive crop protection strategies. Botanical pesticides have been reported to be effective in managing crop pests, and a number of them have been formulated and commercialized. This study was conducted in North-Eastern Tanzania to establish the pesticidal and medicinal value of turmeric ( Curcuma longa) and ginger ( Zingiber officinale). Purposive sampling was adopted to select and in- terview 167 respondents drawn from farmers, traders, pharmaceutical shops, agro-shop operators and consumers of turmeric and ginger. Ginger and tur- meric rhizomes were also collected for extraction, antifungal assay and bio- chemical analysis. Results showed that majority of the respondents were aware of the medicinal value of ginger and turmeric, with 59.5% having used the plants to treat respiratory related infections and healing skin surface and in- ternal wounds. About 14% of farmers were aware of and had used aqueous botanical preparations from neem, moringa and Tephrosia to manage insect pests. Only 2.7% of farmers had used ginger powder as a protective insecticide on stored grains. Ginger and turmeric rhizome extracts showed high antifun- gal activity against Pythium (83% - 95%), Fusarium oxysporum f. sp. lycoper- sici (34% - 52%) and Alternaria solani (38% - 53%). A GC-MS analysis of gin- ger and turmeric extracts showed presence of α-zingiberene, β-sesquiphellan- drene, α-farnesene, ar-curcumene, α-copaene, ar-tumerone and curlone. This study recommends that ginger and turmeric extracts be considered for devel- opment of a botanical pesticide and especially for management of damping off diseases.
Phytochemical activity and role of botanical pesticides in pest management for sustainable agricultural crop production
(Elsevier, 2020-03) Lengai, Geraldin; Muthomi, James; Mbega, Ernest
Increased demand for food to feed the ever-growing population led to development and adoption of synthetic chemicals as a quick and effective strategy of managing crop pests and diseases. However, overreliance on synthetic pesticides is discouraged due to their detrimental effects on human health, the environment, and development of resistant pest and pathogen strains. This, coupled with increasing demand for organically produced foods, stimulated search for alternative approaches and botanical pesticides are particularly gaining importance. Botanical pesticides are efficacious in managing different crop pests, inexpensive, easily biodegraded, have varied modes of action, their sources are easily available and have low toxicity to non-target organisms. Their varied modes of action are attributed to the phytochemical composition in different plants. Therefore, they can be incorporated into integrated pest management systems and contribute to sustainable agricultural production. Nevertheless, botanical pesticides have not been fully adopted due to challenges in formulation and commercialization which are attributed to lack of chemical data and positive controls. Many publications have featured botanical pesticides with skewed interest towards management of insect pests. This review brings together information regarding botanical pesticides, their phytochemical composition and mechanisms of action against pests of importance in agricultural production. The paper also presents chemistry data of selected botanical pesticides, their biodegradation, role in integrated pest management and the challenges facing their adoption and utilization for sustainable crop pest management.
Phytosanitary and Technical Quality Challenges in Export Fresh Vegetables and Strategies to Compliance with Market Requirements: Case of Smallholder Snap Beans in Kenya
(MDPI, 2021-02-02) Fulano, Alex; Lengai, Geraldin; Muthomi, James
Kenya is one of the leading exporters of snap beans (Phaseolus vulgaris) to Europe, but the export volume has remained below potential mainly due to failure to meet the market quality standards. The quality concerns include the presence of regulated and quarantine pests, pesticide residues, harmful organisms, and noncompliance with the technical standards. These challenges call for the development of alternative approaches in overcoming the phytosanitary and quality challenges in the export of snap beans and other fresh vegetables. These may include integrated pest management (IPM) approaches that incorporate non synthetic chemical options, such as diversified cropping systems, plant and microbial-based pesticides, varieties with multiple disease and pest resistance, insecticidal soaps, pheromones and kairomones, entomopathogens and predators. These approaches, coupled with capacity-building and adherence to the set quality standards, will improve compliance with export market requirements. The aim of this paper is to increase knowledge on implementing good practices across the value chain of fresh vegetables that would lead to improved quality and thereby meeting institutional requirements for the export market. The novelty of the current review is using snap beans as a model vegetable to discuss the challenges that must be mitigated for the quest of achieving high quality and increased volume of fresh export products. Whilst many of the publications have focused on alternatives to synthetic pesticides in addressing MRLs in fresh vegetable exports, there is a disconnect between research and industry in achieving chemical residue and pest free export vegetables. This review describes the phytosanitary and technical challenges faced by smallholder farmers in accessing export markets, evaluates the phytosanitary and quality requirements by the niche markets, and explores the strategies that could be used to enhance compliance to the institutional and market requirements for fresh vegetables.