The plant species Elaeodendron buchananii Loes is widely used in folklore medicine to manage microbial infections in Kenya. Previous studies on the plant fruits and root bark revealed the presence of steroids and terpenoids. The present phytochemical analysis of the plant stem bark has led to the isolation of four new triterpenes characterized as methyl 3β-acetoxy-11α, 19α, 28-trihydroxyurs-12-en-23-oic acid (1), 3β, 11α, 19α-trihydroxyurs-12-en-23, 28-dioic acid (2), 3β-acetoxy-19α, 23, 28-trihydroxyurs-12-ene (3) and 3-oxo-19α, 28-dihydroxyurs-12-en-24-oic acid (4), together with ten known ones (5-14), whose structures were elucidated using spectroscopic techniques. The isolate canophyllol (8) showed promising antibacterial activity against N. meningitides with MIC value of 31.25 μg/ml.
Nitrogen fertilisation influences tea yields, quality and pests infestation levels. Red spider mites reduce tea production in western Kenya during prolonged droughts. Nitrogen fertiliser use maybe an agronomic practice that may influence infestation levels by mites. Overhead volatile compounds (OVOCs) composition also influences infestations of tea by mites. Influence of nitrogenous fertiliser rates on red spider mite infestations and OVOCS levels was determined. Mites populations varied (pd>0.05) with nitrogenous fertiliser rates. High infestations were at 0 and 300 kg N/ha/year, and sharp decline between 150 and 225 kg N/ha/year. Green leaf volatiles increased while some aromatic and terpenoid compounds decreased with increasing nitrogenous fertiliser rates. Significant (pd>0.05) direct linear regressions between 1-penten-3-ol, 3-penten- 2-ol, E-2-hexenal, Z-3-hexenyl acetate and inverse relationship between 2-phenyl ethanol, ethyl benzene, -methyl styrene, longifolene and ß-cedrene and nitrogenous fertiliser rates were observed. Most aromatic and terpenoid compounds, which are repellents of mites, were highest between 150 and 225 kg N/ha/year where infestations by mites were lowest. The recommended fertiliser rates of 100 to 225 kg N/ha/year in Kenya also produce most repellents of mites, protecting tea plants against infestations. Use of recommended nitrogen rates can protect tea from infestations by mites.
Tea production in Kenya is under threat due to red crevice mites (Brevipalpus phoenicis) infestations during droughts. Cultural pests control practices, e.g. use of resistant/tolerant cultivars are used in their control since pesticide use is prohibited. Plants release volatile organic compounds (OVOCs) that may influence susceptibility/resistance to pest infestations. OVOCs profiles released by 11 tea cultivars were evaluated to assess relationship between OVOCs and cultivar tolerance/susceptibility to B. phoenicis. Five clones were susceptible, with high B. phoenicis infestations while four clones were resistant, exhibiting low infestation levels. The infestations were linearly correlated to (E)-2-hexenal, (Z)-3-hexenal (p≤0.001), (Z)-3-hexenol, (Z)-3-hexenyl acetate, linalool, germacrene D, sum of green leaf volatiles (GLVs) (p≤0.01), 1-pentene-3-ol, hexanal, indole and (E)-β-ocimene (p≤0.05) levels. Most of aromatic compounds, some terpenoids compounds and sum of aromatic compounds were inversely (p≤0.05) correlated with B. phoenicis infestations. Susceptible varieties to B. phoenicis emitted high amounts of GLVs, especially (E)-2-hexenal, (Z)-3-hexenal, (Z)-3-hexen-1-ol and (Z)-3-hexenyl acetate. Results demonstrate that OVOCs profile may provide selection criteria for cultivars resistant to B. phoenicis infestations. Resistant cultivars are recommended for commercial exploitation in red crevice mites prone areas while breeding/selection programmes should incorporate OVOCs profiles to develop tea cultivars that resist red crevice mites attack.
Mites infestations reduce yields in tea production world wide. However, some tea cultivars are resistant/tolerant to mites attack. The resistance/susceptibility can also be influenced by abiotic factors. This study evaluated some new tea clones for mite resistance/susceptibility and influence of Environmental factors (weather parameters) on dynamics of mite infestations of Kenyan tea at different ecological zones, Kangaita, Kipkebe and Timbilil. Maximum population of mites was reported during March when maximum temperature, average rainfall and relative humidity ranges for the sites were 23.9-28.7°C, 27.7-50.1mm and 38.0-70.4% respectively. There was a sharp decline in mites population in April when average rainfall was high (398.4-514.4mm) which was accompanied by reduction in maximum temperature (18.8-27.5°C) and increase in relative humidity (44.0-82.2%). The minimum population density was found during August which was characterized by low maximum temperature (16.4-26.6°C), low average rainfall (4.8- 190.5mm) and high average relative humidity (46.0-80.9%). The mites infestation levels highly correlated with maximum temperatures in Kangaita (r<sup>2</sup> = 0.801), Kipkebe (r<sup>2</sup> = 0.693) and Timbilil (r<sup>2</sup> = 0.744). There were significant (p≤0.05) monthly variations in clonal mite infestations at all sites. Susceptible clones showed higher monthly mite infestations variations than the resistant/tolerant clones. Of the clones evaluated for the first time, eight new clones were identified as tolerant/resistant while two clones were susceptible to mites attack. Resistant/tolerant clones are recommended for commercial exploitation while mitigation strategies should be put in place in mites prone areas during hot seasons with high monthly temperatures and low humidity
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