Effects of Medicinal Plant Extracts and Photosensitization on Aflatoxin Producing Aspergillus flavus

This study was undertaken with an aim of exploring the effectiveness of medicinal plant extracts in the control of aflatoxin production. Antifungal properties, photosensitization, and phytochemical composition of aqueous and organic extracts of fruits from Solanum aculeastrum, bark from Syzygium cordatum, and leaves from Prunus africana, Ocimum lamiifolium, Lippia kituiensis, and Spinacia oleracea were tested. Spores from four-day-old cultures of previously identified toxigenic fungi, UONV017 and UONV003, were used. Disc diffusion and broth dilution methods were used to test the antifungal activity. The spores were suspended in 2 ml of each extract separately and treated with visible light (420 nm) for varying periods. Organic extracts displayed species and concentration dependent antifungal activity. Solanum aculeastrum had the highest zones of inhibition diameters in both strains: UONV017 (mean = 18.50±0.71 mm) and UONV003 (mean = 11.92±0.94 mm) at 600 mg/ml. Aqueous extracts had no antifungal activity because all diameters were below 8 mm. Solanum aculeastrum had the lowest minimum inhibitory concentration at 25 mg/ml against A. flavus UONV017. All the plant extracts in combination with light reduced the viability of fungal conidia compared with the controls without light, without extracts, and without both extracts and light. Six bioactive compounds were analyzed in the plant extracts. Medicinal plant extracts in this study can control conidia viability and hence with further development can control toxigenic fungal spread

Plant Parasitic Nematodes Associated With Coffee in Kenya and Factors Influencing their Occurrence, Abundance and Diversity

Frequent detection of galls on coffee roots has raised concerns of nematodes in coffee production systems in Kenya. This study aimed at determining the occurrence of nematodes associated with coffee in Kenya and the role of crop management, cultivars, soil properties and agro ecological zones on the abundance and frequency of nematodes. A survey was conducted in the prime coffee growing areas in 10 counties namely; Machakos, Makueni, Kiambu, Embu, Kirinyanga, Nyeri, Meru, Kisii, Nandi and Trans-Nzoia. Nematodes were extracted using a combination of centrifugal floatation and Modified Baermann techniques and identified to genera level.  Nutrient analysis was carried out using the Double Mehlich method. Results showed that nematodes belonging to 30 genera were recovered from coffee agro-ecosystems. Plant parasitic nematodes were the most prevalent with 64% frequency (19 genera) of occurrence followed by bacterial feeders at 24%. The genus Tylenchulus, Meloidogyne and Pratylenchus were the most dominant across all the coffee growing areas. Coffee farms in the coffee-tea zones (Upper Midland 1) harbored the highest numbers of plant parasitic nematodes, followed by Upper Midland 2 and least in the marginal coffee growing zones (Upper Midland 3). Well managed farms had less plant parasitic nematodes compared to neglected farms. K and P significantly contributed to the variation in the nematode community composition. This study demonstrated the prevalence of plant parasitic nematodes, factors that influence their abundance and distribution and justifies need for further management of nematodes in coffee production. Key words: Abundance, agro-ecologial zones, diversity, nematode genera, nutrient

Reaction of Selected Coffee Germplasm to Root-Knot Nematodes in Kenya

Coffee is one of the most important cash crops in Kenya and a leading export earner. Nematodes are among the most important biotic constraint in coffee production in Kenya and crop improvement work has mainly been breeding for resistance to diseases such as coffee berry disease and coffee leaf rust. However resistance has been used successfully in other coffee producing countries and it is one of the most economical and practical nematode management strategies. A greenhouse study was conducted to test the response of local and exotic coffee germplasm to root knot nematodes (RKNs). Ten (10) cultivars provided by Coffee Research Foundation (CRF) were tested for resistance to Meloidogyne incognita under greenhouse conditions (25±2oC). Nematodes were extracted from the roots using Modified Baermann Technique and enumerated using Cobbs slide. After 90 days of plant growth, the disease severity was evaluated and the experiment repeated twice. Galling indices (GI), egg mass indices (EMI) and nematode populations recovered from soil samples indicated a range of responses from resistant to highly susceptible.  Three breeder’s lines including Robusta tree 1, Robusta tree 2 and Robusta tree 3 were rated resistant with galling indices of 1.2-3.0. This study has demonstrated the potential of host resistance as a strategy in the management of nematodes in coffee for increased productivity. Field evaluation needs to be conducted to confirm these findings. The identified resistance sources can be utilized to deploy resistance genes to improve existing varieties that have high commercial value but lack resistance to nematodes.   Key words: Resistance, susceptible, galling indices, nematode population, cultivar

SPATIAL DISTRIBUTION OF TRICHODERMA SP. IN EMBU AND TAITA REGIONS, KENYA

The distribution of Trichoderma species in soils of Embu and Taita regions in Kenya with relation to land use practices was investigated. The study areas were chosen because of their significant land use intensification and for being biodiversity hot spots. Soil washing and dilution plate techniques were used to recover Trichoderma spp from the soil samples collected from different land use types. The fungal isolates were identified and assigned to nine species from Embu soils and eleven species from the Taita soils. Greater populations were however observed in Embu than in Taita. Geographic differences between the regions mostly explain the differences in ecological niches of the two regions that result to different soil assemblages and plant types in the regions and therefore variation in available substrate for the fungus. Land use at each site affected the distribution, richness and abundance of Trichoderma with Napier grass having the highest abundance in both Embu and Taita while coffee had the lowest richness and abundance. Trichoderma favoured plants with shallow and widely spreading rooting systems, compared to the deeply rooted perennial coffee and tea trees. This underpins the importance of plant type and in effect land use system in the abundance of Trichoderma. The unevenness in the distribution of Trichoderma within the LUTs suggests yet another factor influencing the distribution of Trichoderma apart from the LUTs. Unevenness was greater in Embu than in Taita. The differences could mostly be attributed to soil management practices employed by different farmers while managing their land and crops differently. Trichoderma harziunum was the most frequently isolated species and the most abundant in both Embu and Taita. The presence of Trichoderma species in some land use types and the absence in others, provides a clue on the most preferred habitats, plants and/or crops. Considering the beneficial aspects of Trichoderma such as being antagonistic to the pathogenic fungi, crops or plants such as napier grass that induce high abundance and richness of Trichoderma can be used in crop rotations or in combinations with other crops to maintain high levels of the fungus in the soil

INFLUENCE OF LAND USE AND SOIL MANAGEMENT PRACTICES ON THE OCCURRENCE OF NEMATODE DESTROYING FUNGI IN TAITA TAVETA, KENYA

Due to the increased concerns about the effect of agro-chemicals on soil health and soil biodiversity, use of biological methods has become most acceptable alternative methods for farmers to control soil pathogens during crop production. A study was therefore undertaken to determine the occurrence of nematode destroying fungi in Taita Taveta with the aim of isolating and characterizing them for biological control of plant parasitic nematodes. Twenty eight fungal isolates, distributed in three genera, were identified as nematode destroying fungi from all the positive soil samples. Out of the isolates that were identified, 71, 25 and 4 % were in the genera Arthrobotrys, Monacrosporium and Nematoctonus respectively. Arthrobotrys oligospora had an occurrence frequency of 42.9% which was the highest followed by A. dactyloides, M.cionopagum, Monacrosporium sp and Nematoctonus sp with frequencies of 28.6, 17.9 and 7.1and 3.6% respectively. The occurrence of nematode destroying fungi was affected by land use and organic inputs (P ≤ 0.05) while it was not affected by crop rotation (P ≥ 0.05). Napier land use was more diverse than the other land uses with a mean shannon diversity index of 0.717 followed by horticulture (index 0.497). Maize /bean, coffee/beans, fallow and shrub land uses had a mean shannon index of 0. The same trend was observed on richness where napier had a mean richness of 2.2, horticulture 1.8, maize bean 1 while shrub, fallow and coffee/ beans all had mean richness of 0.2. A.oligospora was the most frequently isolated fungi (42.9 %) and showed high potential in biocontrol of plant-parasitic nematodes and was recommended for further studies and development as a biological control agent

Effect of soil fertility management practices on nematode destroying fungi in Taita, Kenya

The effect of soil fertility management practices on nematode destroying fungi was investigated for three seasons in Taita, Kenya. The study aimed at identifying soil fertility practice that promoted nematode destroying fungi in the soil. Field experiments were established in Taita district, the treatments comprised of Mavuno fertilizer, Triple super- phosphate and calcium ammonium nitrate (TSP+CAN), cow manure and a control where no amendments were applied. This experiment was replicated in ten farms and repeated in three planting seasons. Isolation of nematode destroying fungi carried out was using the soil sprinkle technique and the isolates were identified using the key described by Cooke and Godfrey (1964). There were significant difference (P= 1.705 x 10-06) in occurrence of the nematode destroying fungi between soil fertility treatments. The highest mean (1.6) occurrence of nematode destroying fungi was recorded in soils amended with cow manure and the least (0.7) was recorded in soils from the control plots. A mean of 0.78 was recorded in soils from both TSP+CAN and Mavuno fertilizers. Plots amended with cow manure presented the highest diversity of nematodes followed by the control, then TSP+CAN and least in Mavuno with shannon indices of 0.34, 0.15, 0.13 and 0.11 respectively. Sixty percent of all the isolated nematode destroying fungi genera were from plots treated with cow manure and only twenty percent were from plots amended with the inorganic fertilizer. The control plots recorded higher number of nematode destroying fungi compared to the soils that received inorganic fertilizers

Magnetic Concentration of Iron in Lateritic Soils from Kamahuha, Murang’a County, in Kenya using Carbon Monoxide Generated In-Situ

Chemical and Mineral Analyses of laterites from selected sites in Kamahuha area of Murang’a County, in the Republic of Kenya, have been carried out with particular interest in the levels of iron and the type of minerals the iron is present in. A laterite/charcoal mixture was heated in the temperature range 500-700OC as a slow current of air was passed through the hot mixture, the material cooled and the iron-containing mineral picked with a permanent magnet. Elemental Analysis, which was done on both the raw and concentrated samples was carried out using, Atomic Absorption Spectroscopy (AAS). The Analyses also showed that whereas the level of iron in the raw laterites was in the range 28-35, in the magnet –separated product, the level had increased to 55-62% depending on several factors such as how efficiently the laterite-charcoal mixture had been mixed and the length of time of heating.The nature of the minerals present was determined using a Brucker D2 PhaserDiffractometer. In the raw laterites, iron was present as the minerals goethite, FeO.OH and haematite, Fe2O3. These minerals have diffraction peaks at angles 2θ=21.51˚ and 2θ = 54.11, respectively. On the other hand, iron in the magnetpicked product was present predominantly as the mineral magnetite, Fe3O4, as shown by presence of a characteristic peak at 2θ = 36˚. The results of this study show that iron in laterites can be concentrated by magnetic separation after passing compressed air over hot charcoal laterite mixture